Balaev Dmitrii A.

Balaev Dmitrii A.

balaev_da.jpg

Born: august 22, 1971

Address: Kirensky Institute of Physics, Federal Research Center KSC SB RAS,
660036, Krasnoyarsk, Russia

Phone: +7(391) 243-26-35

Fax: 7 (391) 243-89-23

E-mail: dir@iph.krasn.ru
dabalaev@iph.krasn.ru

 

Education:

  • 1993 - Krasnoyarsk State University, Physical department. 

Scientific degree

  • 1997 - Candidate of Physics and Mathematics, Cand. Sci. Dissertation "Transport properties of heterogeneous high-temperature superconductors with inter-crystallite boundaries of metal-type conductivity ".
  • 2010 - Doctor of Physics and Mathematics, Doctoral Dissertation “Mechanisms of magneto-resistive effect in bulk high-temperature superconductors".

Position:

Research interests:

  • Superconductivity
  • Magnetic phenomena
  • Magnetic nanoparticles

Selected works:

  1. D.A. Balaev, A.A. Krasikov, A.A. Dubrovskiy, S.I. Popkov, S.V. Stolyar, O.A. Bayukov, R.S. Iskhakov, V.P. Ladygina, R.N. Yaroslavtsev, Magnetic properties of heat treated bacterial ferrihydrite nanoparticles, Journal of Magnetism and Magnetic Materials, Vol. 410, p.171–180 (2016).
  2. A.A. Dubrovskiy, D.A. Balaev, K.A. Shaykhutdinov, O.A. Bayukov, O.N. Pletnev, S.S. Yakushkin, G.M. Bukhtiyarova, O.N. Martyanov, Size effects in the magnetic properties of ε-Fe2O3 nanoparticles, J. Appl. Phys. 118, 213901 (2015).
  3. D.A. Balaev, I.S. Poperechny, A.A. Krasikov, K.A. Shaikhutdinov, A.A. Dubrovskiy, S.I. Popkov, A.D. Balaev, S.S. Yakushkin, G.A. Bukhtiyarova, O.N. Martyanov, and Yu.L. Raikher, Dynamic magnetization of ε-Fe2O3 in pulse field: Evidence of surface effect, J. Appl. Phys. 117, 063908 (2015).
  4. D. A. Balaev, A. A. Krasikov, A. A. Dubrovskiy, S. V. Semenov, O. A. Bayukov, S. V. Stolyar, R. S. Iskhakov, V. P. Ladygina, L. A. Ishchenko, Magnetic properties and the mechanism of formation of the uncompensated magnetic moment of antiferromagnetic ferrihydrite nanoparticles of a bacterial origin, J. Exp. Theor. Phys. (2014) 119: 479.
  5. D. A. Balaev, D. M. Gokhfeld, S.I. Popkov, K. A. Shaikhutdinov, L. A. Klinkova, L. N. Zherikhina, A.M. Tsvokhrebov, Increase in the Magnetization Loop Width in the Ba0.6K0.4BiO3 Superconductor: Possible Manifestation of Phase Separation, Journal of Experimental and Theoretical Physics, 2014, Vol. 118, No. 1, pp. 104–110.
  6. V.L. Kirillov, D.A. Balaev, S.V. Semenov, K.A. Shaikhutdinov, O.N. Martyanov, Size control in the formation of magnetite nanoparticles in the presence of citrate ions, Materials Chemistry and Physics 145, 75 (2014).
  7. D.A. Balaev, S. V. Semenov, and M. I. Petrov, Correlation Between Magnetoresistance and Magnetization Hysteresis in a Granular High-TC Superconductor: Impact of Flux Compression in the Intergrain Medium, Journal of Superconductivity and Novel Magnetism, Vol. 27, p. 1425–1429 (2014).
  8. Balaev D.A., Dubrovskii A.A., Shaykhutdinov K.A., Bayukov O.A., Yakushkin S.S., Bukhtiyarova G.A. , and Martyanov O.N., Surface Effects and Magnetic Ordering in Few-Nanometer-Sized -Fe2O3 Particles, Journal of Applied Physics. Vol. 114, 163911-5 (2013).
  9. D.A. Balaev, A.A. Dubrovskii, A.A. Krasikov, S.V. Stolyar, R.S. Iskhakov, V.P. Ladygina, and E.D. Khilazheva, Mechanism of the Formation of an Uncompensated Magnetic Moment in Bacterial Ferrihydrite Nanoparticles, JETP Letters, 2013, Vol. 98, No. 3, pp. 139–142.
  10. Balaev D.A., Popkov S.I., Sabitova E.I., Semenov S.V., Shaykhutdinov K.A., Shabanov A.V., Petrov M.I. Compression of a magnetic flux in the intergrain medium of a YBa2Cu3O7 granular superconductor from magnetic and magnetoresistive measurements // Journal of Applied Physics, Vol. 110, № 9. P. 093918 (2011).
  11. Yakushkin S.S., Dubrovskiy A.A., Balaev D.A., Shaykhutdinov K.A., Bukhtiyarova G.A., and Martyanov O.N., Magnetic properties of few nanometers -Fe2O3 nanoparticles supported on the silica, Journal of Applied Physics, Vol. 111 (4), 044312 (2012).
  12. D.A. Balaev, A.A. Bykov, S.V. Semenov, S.I. Popkov, A.A. Dubrovskii, K.A. Shaykhutdinov, M.I. Petrov, General Regularities of Magnetoresistive Effects in the Polycrystalline Yttrium and Bismuth High-Temperature Superconductor Systems, Physics of the Solid State, 53(5) 922 (2011).
  13. D.A. Balaev, A.A. Dubrovskii, K.A. Shaykhutdinov, S.I. Popkov, D.M. Gokhfeld, Yu.S. Gokhfeld, M.I. Petrov, Mechanism of the Hysteretic Behavior of the Magnetoresistance of Granular HTSCs: The Universal Nature of the Width of the Magnetoresistance Hysteresis Loop, JETP 108, 241 (2009).
  14. D.A. Balaev, D.M. Gokhfeld, A.A. Dubrovskii, S.I. Popkov, K.A. Shaykhutdinov, M.I. Petrov, Magnetoresistance Hysteresis in Granular HTSCs as a Manifestation of the Magnetic Flux Trapped by Superconducting Grains in YBCO + CuO Composites, JETP 105, 1174 (2007).
  15. D.A. Balaev, K.A. Shaihutdinov, S.I. Popkov, D.M. Gokhfeld, Petrov M.I. // Magnetoresistive effect of bulk composites 1-2-3 YBCO +CuO and 1-2-3 YBCO+BaPb1-xSnxO3 and their application as magnetic field sensors at 77K // Superconductor Science and Technology. 17 (2004) 175 – 181.
  16. M.I. Petrov, D.A. Balaev, D.M. Gohfeld, S.V. Ospishchev, K.A. Shaihudtinov, K.S. Aleksandrov, Applicability of the theory based on Andreev reflection to the description of experimental current-voltage characteristics of polycrystalline HTSC + normal metal composites, Physica C, Vol. 314 (N1,2), p. 51-54, (1999)
  17. M.I. Petrov, D.A. Balaev, S.V. Ospishchev, K.A. Shaihudtinov, K.S. Aleksandrov. Critical currents in bulk Y3/4Lu1/4Ba2Cu3O7 + BaPbO3 composites. // Phys. Lett. A, 1997, Vol. 237, P.85-89.

New Publications

Uncompensated magnetic moment and surface and size effects in few-nanometer antiferromagnetic NiO particles

Balaev, D. A.; Krasikov, A. A.; Popkov, S., I; Semenov, S., V; Volochaev, M. N.; et al./ Journal Of Magnetism And Magnetic Materials/ https://doi.org/10.1016/j.jmmm.2021.168343

https://doi.org/10.1016/j.jmmm.2021.168343

-The analysis of the M(H) magnetization curves of antiferromagnetic nanoparticles yields information about magnetic subsystems formed in these objects, which are characterized by a large fraction of surface atoms. However, in the conventionally investigated experimental magnetic field range of up to 60–90 kOe, this analysis often faces the ambiguity of distinguishing the Langevin function-simulated contribution of uncompensated magnetic moments μun of particles against the background of a linear-in-field dependence (the antiferromagnetic susceptibility and other contributions). Here, this problem has been solved using a pulsed technique, which makes it possible to significantly broaden the range of external fields in which the μun contribution approaches the saturation. Nanoparticles of a typical NiO antiferromagnet with an average size of <d> ~ 4.5 nm have been investigated. Based on the thorough examination of the M(H) magnetization curves measured in pulsed fields of up to 250 kOe, a model of the magnetic state of NiO nanoparticles of such a small size has been proposed. The average moment is ~130 μB (μB is the Bohr magneton) per particle, which corresponds to 60–70 decompensated spins of nickel atoms localized, according to the Néel hypothesis (μun ~ <d>3/2), both on the surface and in the bulk of a particle. A part of the surface spins unrelated to the antiferromagnetic core form another subsystem, which behaves as free paramagnetic atoms. Along with the antiferromagnetic core, an additional linear-in-field contribution has been detected, which is apparently related to superantiferromagnetism, i.e., the size effect inherent to small antiferromagnetic particles.

Interparticle magnetic interactions in synthetic ferrihydrite: Mossbauer spectroscopy and magnetometry study of the dynamic and static manifestations

Knyazev, Yu, V; Balaev, D. A.; Stolyar, S., V; Krasikov, A. A.; Bayukov, O. A.; et al./ Journal Of Alloys And Compounds/ https://doi.org/10.1016/j.jallcom.2021.161623

https://doi.org/10.1016/j.jallcom.2021.161623

Samples of synthetic ferrihydrite with an average nanoparticle size of 2.7 nm have been examined by magnetometry and Mössbauer spectroscopy. Ferrihydrite is characterized by the antiferromagnetic interactions between the magnetic moments of iron atoms. In ferrihydrite nanoparticles, as in any other antiferromagnetic ones, structural defects induce the formation of an uncompensated magnetic moment, which determines the magnetic properties typical of single-domain ferro- and ferrimagnetic particles. The manifestation of the magnetic interactions between ferrihydrite nanoparticles in the magnetic properties of the material and in the temperature evolution of Mössbauer spectra has been in focus. The results obtained on synthetic ferrihydrite have been compared with the data for the biogenic ferrihydrite sample with a similar average size of particles surrounded by a polysaccharide shell, which weakens and screens the interparticle magnetic interactions. A clear manifestation of the effect of the interparticle magnetic interactions on the transition to the blocked state is the presence of a significant contribution of the relaxation component in the Mössbauer spectra at temperatures of the transition from the superparamagnetic to blocked state. The temperature dependence of the particle relaxation time obtained from the Mössbauer spectra points out the collective effect of freezing of the magnetic moments of particles due to the magnetic interactions between them.

Interplay of Magnetic and Superconducting Subsystems in Ho-Doped YBCO

Gokhfeld, D. M.; Semenov, S., V; Terentyev, K. Yu; Yakimov, I. S.; Balaev, D. A. Journal Of Superconductivity And Novel Magnetism. https://doi.org/10.1007/s10948-021-05954-3

Superconducting and paramagnetic contributions to the magnetization of polycrystalline Y1−xHoxBa2Cu3O7−δ samples were investigated. The superconductivity is responsible for a partial screening of magnetic ions from an external magnetic field and for a possible sinking of antiferromagnetic correlations between these ions. Magnetic moments of Ho ions influence on a peak effect induced by the order–disorder transition of the Abrikosov vortex lattice. The critical current density and the critical temperature of YBCO are not changed by the Ho doping.

https://doi.org/10.1007/s10948-021-05954-3

High-Temperature Evolution of the Magnetization of Aluminum Reduction Cell Steel

Balaev, Dmitry A.; Semenov, Sergei, V; Varnakov, Sergei N.; Radionov, Evgeniy Yu; Al Tretyakov, Yaroslav. Journal Of Siberian Federal University-mathematics & Physics DOI: https://doi.org/10.17516/1997-1397-2021-14-1-5-11

The magnetic properties of steel of a structural element of an aluminum reduction cell have been investigated in the temperature range of 300–900 K. The analysis of the temperature dependence of the saturation magnetization MS(T) showed (i) the applicability of the Bloch’s 3/2 law and a reasonable value of the Bloch’s constant for steel and (ii) the quadratic dependence MS(T)∼(1 − T 2 ) in the temperature range of 380–700 K.

DOI: https://doi.org/10.17516/1997-1397-2021-14-1-5-11

Collective Spin Glass State in Nanoscale Particles of Ferrihydrite

Stolyar, S., V; Yaroslavtsev, R. N.; Ladygina, V. P.; Balaev, D. A.; Pankrats, A., I; et al. Semiconductors. DOI https://doi.org/10.1134/S1063782620120362

Ferromagnetic resonance was used to study three types of ferrihydrite nanoparticles: nanoparticles formed as a result of the cultivation of microorganisms Klebsiella oxytoca; chemically prepared ferrihydrite nanoparticles; chemically prepared ferrihydrite nanoparticles doped with Cu. It is established from the ferromagnetic resonance data that the frequency-field dependence (in the temperature range ТP < T < T*) is described by the expression: 2πν/γ = НR + HA(T = 0)(1 – T/Т*), where γ is the gyromagnetic ratio, HR is the resonance field. The induced anisotropy HA is due to the spin-glass state of the near-surface regions. TP temperature characterizes the energy of the interparticle interaction of nanoparticles.

New Evidence of Interaction Between Grain and Boundaries Subsystems in Granular High-Temperature Superconductors

Balaev, D. A.; Semenov, S. V.; Gokhfeld, D. M. Journal Of Superconductivity And Novel Magnetism. DOI https://doi.org/10.1007/s10948-021-05812-2

Granular high-temperature superconductors (HTSs) exhibit magnetotransport properties, including the clockwise magnetoresistance hysteresis. The hysteresis is explained by the concept of an effective field in the subsystem of grain boundaries, where the observed dissipation occurs. The effective field in the intergrain medium is determined by a superposition of the external field H and the field induced by the magnetic response of HTS grains. The magnetic flux compression in the intergrain medium provides an increase of the effective field. The magnetoresistance hysteresis of polycrystalline YBa2Cu3O7-δ has a bright feature: In a fairly wide external field range, the hysteresis width ΔH(H) is found to be almost linear, ΔH ≈ H. This behavior is considered to be universal over the entire temperature range corresponding to the superconducting state (the investigations have been carried out at temperatures of 77 K and 4.2 K). The analysis of the magnetoresistive and magnetic properties has shown that the upper boundary of the field range of the ΔH ≈ H regime is consistent with the field of complete penetration into HTS grains. This is indicative of the strong interrelation between the magnetotransport and magnetic properties of granular HTSs.

Features of the quasi-static and dynamic magnetization switching in NiO nanoparticles: Manifestation of the interaction between magnetic subsystems in antiferromagnetic nanoparticles

D.A.Balaev, A.A.Krasikov, S.I.Popkov, A.A.Dubrovskiy, S.V.Semenov, D.A.Velikanov, V.L.Kirillov, O.N.Martyanov. JMMM https://doi.org/10.1016/j.jmmm.2020.167307

We report on the investigations of a system of 8-nm NiO particles representing antiferromagnetic (AFM) materials, which are weak magnetic in the form of submicron particles, but can be considered to be magnetoactive in the form of nanoparticles due to the formation of the uncompensated magnetic moment in them. The regularities of the behavior of magnetization switching in AFM nanoparticles are established by studying the magnetic hysteresis loops under standard quasi-static conditions and in a quasi-sinusoidal pulsed field of up to 130 kOe with pulse lengths of 4–16 ms. The magnetic hysteresis loops are characterized by the strong fields of the irreversible magnetization behavior, which is especially pronounced upon pulsed field-induced magnetization switching. Under the pulsed field-induced magnetization switching conditions, which are analogous to the dynamic magnetic hysteresis, the coercivity increases with an increase in the maximum applied field H0 and a decrease in the pulse length. This behavior is explained by considering the flipping of magnetic moments of particles in an external ac magnetic field; however, in contrast to the case of single-domain ferro- and ferrimagnetic particles, the external field variation rate dH/dt is not a universal parameter uniquely determining the coercivity. At the dynamic magnetization switching in AFM nanoparticles, the H0 value plays a much more important role. The results obtained are indicative of the complex dynamics of the interaction between magnetic subsystems formed in AFM nanoparticles.

General Regularities and Differences in the Behavior of the Dynamic Magnetization Switching of Ferrimagnetic (CoFe2O4) and Antiferromagnetic (NiO) Nanoparticles

Popkov, S. I.; Krasikov, A. A.; Semenov, S. V.; Dubrovskii, A. A.; Yakushkin, S. S.; et al. Physics Of The Solid State. DOI https://doi.org/10.1134/S1063783420090255

In antiferromagnetic (AFM) nanoparticles, an additional ferromagnetic phase forms and leads to the appearance in AFM nanoparticles of a noncompensated magnetic moment and the magnetic properties typical of common FM nanoparticles. In this work, to reveal the regularities and differences of the dynamic magnetization switching in FM and AFM nanoparticles, the typical representatives of such materials are studied: CoFe2O4 and NiO nanoparticles with average sizes 6 and 8 nm, respectively. The high fields of the irreversible behavior of the magnetizations of these samples determine the necessity of using strong pulsed fields (amplitude to 130 kOe) to eliminate the effect of the partial hysteresis loop when studying the dynamic magnetic hysteresis. For both types of the samples, coercive force HC at the dynamic magnetization switching is markedly higher than HC at quasi-static conditions. HC increases as the pulse duration τP decreases and the maximum applied field H0 increases. The dependence of HC on field variation rate dH/dt = H0/2τP is a unambiguous function for CoFe2O4 nanoparticles, and it is precisely such a behavior is expected from a system of single-domain FM nanoparticles. At the same time, for AFM NiO nanoparticles, the coercive force is no longer an unambiguous function of dH/dt, and the value of applied field H0 influences more substantially. Such a difference in the behaviors of FM and AFM nanoparticles is caused by the interaction of the FM subsystem and the AFM “core” inside AFM nanoparticles. This circumstance should be taken into account when developing the theory of dynamic hysteresis of the AFM nanoparticles and also to take into account their practical application.

Collective Spin Glass State in Nanoscale Particles of Ferrihydrite

Stolyar, S., V; Yaroslavtsev, R. N.; Ladygina, V. P.; Balaev, D. A.; Pankrats, A., I; et al. Semiconductors. https://doi.org/10.1134/S1063782620120362

Ferromagnetic resonance was used to study three types of ferrihydrite nanoparticles: nanoparticles formed as a result of the cultivation of microorganisms Klebsiella oxytoca; chemically prepared ferrihydrite nanoparticles; chemically prepared ferrihydrite nanoparticles doped with Cu. It is established from the ferromagnetic resonance data that the frequency-field dependence (in the temperature range ТP < T < T*) is described by the expression: 2πν/γ = НR + HA(T = 0)(1 – T/Т*), where γ is the gyromagnetic ratio, HR is the resonance field. The induced anisotropy HA is due to the spin-glass state of the near-surface regions. TP temperature characterizes the energy of the interparticle interaction of nanoparticles.

Magnetic anisotropy and core-shell structure origin of the biogenic ferrihydrite nanoparticles

Knyazev, Yu, V; Balaev, D. A.; Stolyar, S., V; Bayukov, O. A.; Yaroslavtsev, R. N.; et al. Journal Of Alloys And Compounds. https://doi.org/10.1016/j.jallcom.2020.156753

Ferrihydrite is a low-crystalline nanoscale matter. The uncompensated magnetic moment of the ferrihydrite caused by the antiferromagnetic ordering of the magnetic moments of iron atoms and leads to the magnetic properties very similar to those of ferro- and ferrimagnetic nanoparticles. In this study, we investigated the biogenic ferrihydrite nanoparticles with the narrow size distribution and an average diameter of 2 nm obtained by the bacteria life cycle. The features caused by the surface effects and the inhomogeneous structure of ferrihydrite have been examined in the temperature range of 4–300 K using Mössbauer spectroscopy and magnetometry. Based on the Mössbauer data, we identified the superparamagnetic blocking temperature at the temperature of 30 K for the largest ferryhidrite particles. We established that the exceptional magnetic anisotropy of ferrihydrite (KV=1.2⋅105 erg/cm3 and KS=0.1 erg/cm2) is reached because of the highly developed ferrihydrite nanoparticles’ surface. According to the Mössbauer data, we propose a core-shell structural model of the biogenic ferrihydrite particles. We found that the size of the dense core depends on the particle size. The well-crystallized core is formed only for nanoparticles larger than 2 nm, whereas smaller particles consist entirely of a matter with a lower density of iron atoms.

Features of the Pulsed Magnetization Switching in a High-Coercivity Material Based on epsilon-Fe2O3 Nanoparticles

Popkov, S. I.; Krasikov, A. A.; Semenov, S. V.; с соавторами. PHYSICS OF THE SOLID STATE. DOI: 10.1134/S1063783420030166

The magnetic structure of the epsilon-Fe2O3 iron oxide polymorphic modification is collinear ferrimagnetic in the range from room temperature to similar to 150 K. As the temperature decreases, epsilon-Fe2O3 undergoes a magnetic transition accompanied by a significant decrease in the coercivity H-c and, in the low-temperature range, the compound has a complex incommensurate magnetic structure. We experimentally investigated the dynamic magnetization switching of the epsilon-Fe2O3 nanoparticles with an average size of 8 nm in the temperature range of 80-300 K, which covers different types of the magnetic structure of this iron oxide. A bulk material consisting of xerogel SiO2 with the epsilon-Fe2O3 nanoparticles embedded in its pores was examined. The magnetic hysteresis loops under dynamic magnetization switching were measured using pulsed magnetic fields H-max of up to 130 kOe by discharging a capacitor bank through a solenoid. The coercivity H-c upon the dynamic magnetization switching noticeably exceeds the H-c value under the quasi-static conditions. This is caused by the superparamagnetic relaxation of magnetic moments of particles upon the pulsed magnetization switching. In the range from room temperature to similar to 150 K, the external field variation rate dH/dt is the main parameter that determines the behavior of the coercivity under the dynamic magnetization switching. It is the behavior that is expected for a system of single-domain ferro- and ferrimagnetic particles. Under external conditions (at a temperature of 80 K) when the epsilon-Fe2O3 magnetic structure is incommensurate, the coercivity during the pulsed magnetization switching depends already on the parameter dH/dt and is determined, to a great extent, by the maximum applied field H-max. Such a behavior atypical of systems of ferrimagnetic particles is caused already by the dynamic spin processes inside the epsilon-Fe2O3 particles during fast magnetization switching.

Magnetization Anisotropy in the Textured Bi-2223 HTS in Strong Magnetic Fields

Gokhfeld, D. M.; Balaev, D. A. Physics Of The Solid State. DOI https://doi.org/10.1134/S1063783420070069

The origin of the low magnetization anisotropy of the textured bulk samples consisting of highly anisotropic (Bi,Pb)2Sr2Ca2Cu3Ox (Bi-2223) high-temperature superconductor crystallites has been investigated. It has been established that the observed anisotropy is determined by the disordering of Bi-2223 crystallites in the sample. The measured anisotropy of the textured sample makes it possible to determine the magnetic angle characterizing the ordering of crystallites.

Model of the Behavior of a Granular HTS in an External Magnetic Field: Temperature Evolution of the Magnetoresistance Hysteresis

Semenov, S. V.; Balaev, D. A. Physics Of The Solid State. https://doi.org/10.1134/S1063783420070239

A model for describing the magnetoresistance behavior in a granular high-temperature superconductor (HTS) that has been developed in the last decade explains a fairly extraordinary form of the hysteretic R(H) dependences at T = const and their hysteretic features, including the local maximum, the negative magnetoresistance region, and the local minimum. In the framework of this model, the effective field Beff in the intergrain medium has been considered, which represents a superposition of the external field and the field induced by the magnetic moments of HTS grains. This field can be written in the form Beff(H) = H + 4παM(H), where M(H) is the experimental field dependence of the magnetization and α is the parameter of crowding of the magnetic induction lines in the intergrain medium. Therefore, the magnetoresistance is a function of not simply an external field, but also the “internal” effective field R(H) = f(Beff(H)). The magnetoresistance of the granular YBa2Cu3O7 – δ HTS has been investigated in a wide temperature range. The experimental hysteretic R(H) dependences obtained in the high -temperature range (77–90 K) are well explained using the developed model and the parameter α is 20–25. However, at a temperature of 4.2 K, no local extrema are observed, although the expression for Beff(H) predicts them and the parameter α somewhat increases (~30–35) at this temperature. An additional factor that must be taken into account in this model can be the redistribution of the microscopic current trajectories, which also affects the dissipation in the intergrain medium. At low temperatures under the strong magnetic flux compression (α ~ 30–35), the microscopic trajectories of the current Im can change and tunneling through the neighboring grain is preferred, but the angle between Im and Beff will be noticeably smaller than 90°, although the external (and effective) field direction is perpendicular to the macroscopic current direction.

Features of Relaxation of the Remanent Magnetization of Antiferromagnetic Nanoparticles by the Example of Ferrihydrite

Balaev, D. A.; Krasikov, A. A.; Balaev, A. D.; Stolyar, S. V.; Ladygina, V. P.; et al. Physics Of The Solid State. https://doi.org/10.1134/S1063783420070033

The relaxation of the remanent magnetization of antiferromagnetically ordered ferrihydrite nanoparticles at the exchange bias effect implemented in these systems has been investigated. The magnetization relaxation depends logarithmically on time, which is typical of the thermally activated hoppings of particle magnetic moments through the potential barriers caused by the magnetic anisotropy. The barrier energy obtained by processing of the remanent magnetization relaxation data under the field cooling conditions significantly exceeds the barrier energy under standard (zero field cooling) conditions. The observed difference points out the possibility of using the remanent magnetization relaxation to analyze the mechanisms responsible for the exchange bias effect in antiferromagnetic nanoparticles and measure the parameters of the exchange coupling of magnetic subsystems in such objects.

Ferromagnetic Resonance Study of Biogenic Ferrihydrite Nanoparticles: Spin-Glass State of Surface Spins

Stolyar, S., V; Balaev, D. A.; Ladygina, V. P.; Pankrats, A., I; Yaroslavtsev, R. N.; et al. Jetp Letters. DOI: 10.1134/S0021364020030145

Ferrihydrite nanoparticles (2–3 nm in size), which are products of the vital activity of microorganisms, are studied by the ferromagnetic resonance method. The “core” of ferrihydrite particles is ordered antiferromagnetically, and the presence of defects leads to the appearance of an uncompensated magnetic moment in nanoparticles and the characteristic superparamagnetic behavior. It is established from the ferromagnetic resonance data that the field dependence of the frequency is described by the expression = , where γ is the gyromagnetic ratio, is the resonance field, kOe, and K. The induced anisotropy is due to the spin-glass state of the near-surface regions.

Nuclear forward scattering application to the spiral magnetic structure study in epsilon-Fe2O3

Knyazev, Yu, V; Chumakov, A., I; Dubrovskiy, A. A.; Semenov, S., V; Sergueev, I. Yakushkin, V. L. Kirillov, O. N. Martyanov, and D. A. Balaev Physical Review B. DOI: 10.1103/PhysRevB.101.094408

The -Fe2O3 magnetic structure has been analyzed using the synchrotron radiation source. Time spectra of nuclear forward scattering for isolated nanoparticles with an average size of 8 nm immobilized in a xerogel matrix have been recorded in the temperature range of 4–300 K in applied magnetic fields of 0–4 T in the longitudinal direction at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). It has been found that the external magnetic field does not qualitatively change the Hhf (T) behavior, but makes a strong opposite impact on the hyperfine fields in the nonequivalent iron sites, leading to the divergence of Hhf polar angle dependences below 80 K. A complete diagram of the -Fe2O3 magnetic structure in the temperature range of 4–300 K is proposed. At 300 K, the -Fe2O3 compound is confirmed to be a collinear ferrimagnet. The experimental results show that the magnetic transition at 150–80 K leads to the formation of a noncollinear magnetic structure. Furthermore, in the range of the 80–4 K, the ground state of a magnetic spiral is established. The experimental results are supplemented by the analysis of the exchange interactions and temperature dependence of the magnetization in a magnetic field of 7 T.

Synthesis and Magnetic Properties of the Core-Shell Fe3O4/CoFe2O4 Nanoparticles

Balaev, D. A.; Semenov, S. V.; Dubrovskii, A. A.; Krasikov, A. A.; Popkov, S. I. S. S. Yakushkin, V. L. Kirillov, and O. N. Mart’yanov Physics Of The Solid State. doi:10.1134/s1063783420020043

The Fe3O4/CoFe2O4 nanoparticles with a core–shell structure with an average size of 5 nm have been obtained by codeposition from the iron and cobalt chloride solutions. An analysis of the magnetic properties of the obtained system and their comparison with the data for single-phase Fe3O4 (4 nm) and CoFe2O4 (6 nm) nanoparticles has led to the conclusion about a noticeable interaction between the soft magnetic (Fe3O4) and hard magnetic (CoFe2O4) phases forming the core and shell of hybrid particles.

Mossbauer Study of the Magnetic Transition in epsilon-Fe2O3 Nanoparticles Using Synchrotron and Radionuclide Sources

Knyazev, Yu. V.; Chumakov, A. I.; Dubrovskiy, A. A.; at all JETP LETTERS, DOI: 10.1134/S0021364019210082

 Nuclear gamma-resonance experiments with energy and time resolved detection are carried out with epsilon-F2O3 nanoparticles and a Co-57(Rh) laboratory Mossbauer source of gamma radiation and a 14.4125 keV synchrotron radiation source on the ID18 beamline (ESRF) in the temperature range of 4-300 K. Both methods show a tremendous increase in the hyperfine field in tetrahedrally coordinated iron positions during the magnetic transition in the range of 80-150 K. As a result, the splitting of the quantum beat peaks in the nuclear scattering spectra is observed in the time interval of 20-170 ns with a periodicity of similar to 30 ns. In addition, the first quantum beat is slightly shifted to shorter times. A correlation between the quadrupole shift and the orbital angular momentum of iron in epsilon-F2O3 nanoparticles is found. The magnetic transition leads to the rotation of the magnetic moment in the tetrahedral positions of iron around the axis of the electric field gradient by an angle of 44 degrees.

The Low-Temperature Magnetic State and Magnetic Ordering Temperature of -Fe 2 O 3 Iron Oxide Nanoparticles

Dubrovskiy, Andrey A.; Semenov, Sergey V.; Knyazev, Yuri V.; Popkov, Sergey I.; Yakushkin, Stas S.; et al. Ieee Magnetics Letters. DOI: 10.1109/LMAG.2019.2956674

The -Fe2O3 iron oxide polymorph is a well-known magnetic material with a complex magnetic structure, which undergoes a series of magnetic transitions in different temperature ranges. However, the -Fe2O3 phase diagram is still unclear. We report on the magnetic properties of a sample consisting of -Fe2O3 nanoparticles with an average size of 8 nm embedded in a SiO2 xerogel matrix without an admixture of foreign phases. Along with the features typical of the well-known -Fe2O3 magnetic transition in the temperature range 80150 K, the temperature dependence of magnetization M(T) of -Fe2O3 includes other low-temperature anomalies. In an external field of H 70kOe, there is a noticeable temperature hysteresis of magnetization at 5090 K, and near T & approx; 50 K, the M(T) curves have a characteristic bending, which may be indicative of an additional magnetic transition. The ferromagnetic resonance spectra shows that, near 500 K, a magnetic phase transition occurs, which was previously thought to be a transition to the paramagnetic state. An analysis of the temperature dependence of the ferromagnetic resonance spectra shows that the magnetically ordered phase in -Fe2O3 exists up to about 800 K.

Size effects in the formation of an uncompensated ferromagnetic moment in NiO nanoparticles

Popkov, S., I; Krasikov, A. A.; Dubrovskiy, A. A.; Volochaev, M. N.; Kirillov, V. L.; Martyanov, O. N.; Balaev, D. A. Source: JOURNAL OF APPLIED PHYSICS, 126 (10):10.1063/1.5109054 SEP 14 2019

The magnetic properties of samples of NiO nanoparticles with average sizes of 23, 8.5, and 4.5 nm were investigated. Using the magnetization curves measured in strong (up to 250 kOe) pulsed magnetic fields, the contributions of the free spin and ferromagnetic subsystems were extracted. It has been found that the ferromagnetic contribution increases with a decrease in the nanoparticle size and is proportional to the fraction of uncompensated exchange-coupled spins. It is demonstrated that the uncompensated spins form in the antiferromagnetic NiO oxide due to an increase in the fraction of surface atoms in the nanoparticles with decreasing particle size and defects in the bulk of particles

Magnetoresistance Hysteresis Evolution in the Granular Y-Ba-Cu-O High-Temperature Superconductor in a Wide Temperature Range

Semenov, S. V.; Balaev, D. A. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (8):2409-2419; 10.1007/s10948-019-5043-2 AUG 2019

The temperature evolution of the magnetoresistance hysteresis in the granular YBa2Cu3O7-δ high-temperature (TC ≈ 92 K) superconductor has been investigated. The measurements have been performed in the high-temperature region (78–90 K) and at the liquid helium temperature (4.2 K). The results obtained have been analyzed using the developed model of the behavior of transport properties of a granular high-temperature superconductor in an external magnetic field. Within the discussed model, the dissipation of the grain boundary subsystem is determined by the intergrain spacing-averaged effective field Beff, which is a superposition of external field H and the field induced by the magnetic moments of superconducting grains. Such a consideration yields the expression Beff(H) = H − 4πM(H) α for the effective field in the intergrain medium, where M(H) is the experimental hysteretic dependence of magnetization and α is the parameter of magnetic flux crowding in the intergrain medium. Here, the magnetoresistance is assumed to be proportional to the absolute value of the effective field: R(H) ~ |Beff(H)|. Analysis of the experimental R(H) and M(H) dependences obtained under the same conditions for the investigated high-temperature superconductor sample showed that in the high-temperature region this parameter is α ≈ 25. At the low temperature (4.2 K), we may state that the degree of flux crowding increases and the estimated α value is ~ 50. The estimates made are indicative of the strong effect of flux compression in the intergrain medium on the magnetotransport properties of the investigated granular high-temperature superconductor system. Possible reasons for a discrepancy between the developed model concepts and experimentally observed low-temperature R(H) hysteresis are analyzed.

Tunnel Conductivity and Tunnel Magnetoresistance of the Fe-SiO Films: Interplay of the Magnetotransport and Magnetic Properties

Balaev, D. A.; Balaev, A. D. Source: PHYSICS OF THE SOLID STATE, 61 (7):1203-1210; 10.1134/S1063783419070047 JUL 2019

The electrical properties of a system of nanogranular amorphous Fe–SiO films with a SiO concentration between 0 and 92 vol % have been investigated. The samples with a low SiO content are characterized by the metal-type conductivity. With an increase in the dielectric content x in the films, the concentration transition from the metal to tunneling conductivity occurs at x ≈ 0.6. At the same concentration, the ferromagnet–superparamagnet transition is observed, which was previously investigated by the magnetic method. The temperature dependences of the electrical resistivity ρ(T) for the compositions corresponding to the dielectric region obey the law ρ(T) ~ exp(2(C/kT)1/2), which is typical of the tunneling conductivity. The estimation of the metal grain sizes from the tunneling activation energy C has shown good agreement with the sizes obtained previously by analyzing the magnetic properties. In the dielectric region of the compositions, the giant magnetoresistive effect attaining 25% at low temperatures has been obtained.

Formation of the magnetic subsystems in antiferromagnetic NiO nanoparticles using the data of magnetic measurements in fields up to 250 kOe

Popkov, S., I; Krasikov, A. A.; Velikanov, D. A.; Kirillov, V. L.; Martyanov, O. N.; Balaev, D. A. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 483 21-26; 10.1016/j.jmmm.2019.03.004 AUG 1 2019

It is well-known that the fraction of surface atoms and the number of defects in an antiferromagnetic particle increase with a decrease in the particle size to tens of nanometers, which qualitatively changes the properties of the particle. Specifically, in antiferromagnetic nanoparticles, spins in the ferromagnetically ordered planes can partially decompensate; as a result, an antiferromagnetic particle acquires a magnetic moment. As a rule, uncompensated chemical bonds of the surface atoms significantly weaken the exchange coupling with the antiferromagnetic particle core, which can lead to the formation of an additional magnetic subsystem paramagnetic at high temperatures and spin-glass-like in the low-temperature region. The existence of several magnetic subsystems makes it difficult to interpret the magnetic properties of antiferromagnetic nanoparticles. It is shown by the example of NiO nanoparticles with an average size of 8 nm that the correct determination of the contributions of the magnetic subsystems forming in antiferromagnetic nanoparticles requires magnetic measurements in much stronger external magnetic fields than those commonly used in standard experiments (up to 60–90 kOe). An analysis of the magnetization curves obtained in pulsed magnetic fields up to 250 kOe allows one to establish the contributions of the uncompensated particle magnetic moment μun, paramagnetic subsystem, and antiferromagnetic particle core. The μun value obtained for the investigated NiO particles is consistent with the Néel model, in which μun ∼ N1/2 (N is the number of magnetically active atoms in a particle), and thereby points out the existence of defects on the surface and in the bulk of a particle. It is demonstrated that the anomalous behavior of the high-field susceptibility dM/dH of antiferromagnetic NiO nanoparticles, which was observed by many authors, is caused by the existence of a paramagnetic subsystem, rather than by the superantiferromagnetism effect.

Temperature of the Magnetic Ordering of the Trivalent Iron Oxide epsilon-Fe2O3

Balaev, D. A.; Dubrovskiy, A. A.; Yakushkin, S. S.; Bukhtiyarova, G. A.; Martyanov, O. N. Source: PHYSICS OF THE SOLID STATE, 61 (3):345-349; 10.1134/S1063783419030053 MAR 2019

The trivalent iron oxide ε-Fe2O3 is a fairly rare polymorphic iron oxide modification, which only exists in the form of nanoparticles. This magnetically ordered material exhibits an intriguing magnetic behavior, specifically, a significant room-temperature coercivity HC (up to ~20 kOe) and a magnetic transition in the temperature range of 80–150 K accompanied by a sharp decrease in the HC value. Previously, the temperature of the transition to the paramagnetic state for ε-Fe2O3 was believed to be about 500 K. However, recent investigations have shown that the magnetically ordered phase exists in ε-Fe2O3 also at higher temperatures and, around 500 K, another magnetic transition occurs. Using the data on the magnetization and temperature evolution of the ferromagnetic resonance spectra, it is shown that the temperature of the transition of ε-Fe2O3 particles 3–10 nm in size to the paramagnetic state is ~850 K.

Dimethylsulfoxide as a media for one-stage synthesis of the Fe3O4-Based ferrofluids with a controllable size distribution

Kirillov, V. L.; Yakushkin, S. S.; Balaev, D. A.; Dubrovskiy, A. A.; Semenov, S. V.; Knyazev, Yu. V.; Bayukov, O. A.; Velikanov, D. A.; Yatsenko, D. A.; Martyanov, O. N. Source: MATERIALS CHEMISTRY AND PHYSICS, 225 292-297; 10.1016/j.matchemphys.2019.01.003 MAR 1 2019

The ultrafine (d = 4 nm) magnetite ferrofluid with a narrow nanoparticle size distribution has been synthesized in one stage at room temperature from a solution of iron(II) and (III) chlorides in dimethylsulfoxide (DMSO) with the propylene epoxide admixture. This is the first example of obtaining a stable concentrated ultrafine magnetite/DMSO ferrofluid at room temperature. X-ray diffraction, transmission electron microscopy, ferromagnetic resonance, Mössbauer spectroscopy, and magnetostatic study have been used to elucidate the role of DMSO and the H2O/DMSO ratio in the formation of a stable colloid with a desired nanoparticle size. The initial stages of the magnetite nanoparticles formation have been investigated by the ferromagnetic resonance technique.

In Situ FMR Study of the Selective H2S-Oxidation Stability of epsilon-Fe2O3/SiO2 Catalysts

Yakushkin, S. S.; Bukhtiyarova, G. A.; Dubrovskiy, A. A.; Knyazev, Yu. V.; Balaev, D. A.; Martyanov, O. N. Source: APPLIED MAGNETIC RESONANCE, 50 (5):725-733; 10.1007/s00723-019-1109-3 MAY 2019

The stability of a catalyst for partial H2S oxidation has been studied by the ferromagnetic resonance (FMR) technique combined with transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and magnetostatic investigations. The ε-Fe2O3 iron oxide nanoparticles supported on silica have been examined for their stability under the selective H2S oxidation conditions. The combination of the physicochemical methods has been used to study the state of reacted catalysts. The ε-Fe2O3 phase has been found to remain stable under the selective H2S oxidation conditions at temperatures up to 300 °C. The active phase state during the catalytic reaction has been explored using in situ FMR experiments. It has been established that the ε-Fe2O3 nanoparticles retain their structure and magnetic properties in the presence of H2S at high temperatures. During the in situ FMR experiments, the ε-Fe2O3 sulfidation process has been studied.

Dynamic Magnetization Switching in NiO Nanoparticles: Pulsed Field Magnetometry Study

Balaev, D. A.; Krasikov, A. A.; Dubrovskiy, A. A.; Balaev, A. D.; Popkov, S. I.; Kirillov, V. L.; Martyanov, O. N. Source: JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 32 (2):405-411; 10.1007/s10948-018-4726-4 FEB 2019

The dynamic magnetization switching of antiferromagnetic nickel oxide nanoparticles with a characteristic size of 8 nm has been experimentally investigated by pulsed field magnetometry. It is shown that, due to the presence of defects in NiO nanoparticles, as in other antiferromagnetic particles, the uncompensated magnetic moment is induced by the incomplete compensation of spins at the antiferromagnetic ordering. The dynamic magnetic hysteresis loops have been studied in pulsed fields with the maximum field (Hmax) of up to 130 kOe and pulse lengths (τP) of 4, 8, and 16 ms. According to the results obtained, the coercivity (HC) depends on both the τP and Hmax values. The observed increase in the HC value with decreasing pulse length (i.e., with increasing switching field frequency) is unambiguously related with the relaxation processes typical of single-domain ferromagnetic nanoparticles. However, the observed effect of the maximum applied field (Hmax) on the HC value is assumed to be a feature of antiferromagnetic nanoparticles.

Magnetic and thermodynamic properties and spin-flop-driven magnetodielectric response of the antiferromagnetic Pb2Fe2Ge2O9 single crystals

Pankrats, A. I.; Balaev, D. A.; Nikitin, S. E.; Freydman, A. L.; Krasikov, A. A.; Balaev, A. D.; Popkov, S. I.; Kolkov, M. I. Source: JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 479 114-120; 10.1016/j.jmmm.2019.02.026 JUN 1 2019

Orthorhombic Pb2Fe2Ge2O9 antiferromagnetic single crystals have been synthesized by a modified pseudo-flux technique and their magnetic, thermodynamic, and magnetodielectric properties have been investigated. It has been found that, below the Neel temperature (45.2 K), iron moments are arranged in a canted antiferromagnetic structure with a weak ferromagnetic moment parallel to the a axis. According to the specific heat measurement data, the TN value remains invariable in applied magnetic fields of up to 50 kOe within the experimental accuracy. The magnetic entropy in the investigated crystals attains 2Rln(2S + 1) right above TN, which is indicative of a purely magnetic nature of the transition. It has been shown that the weak ferromagnetic moment is induced by the interplay between the single-ion anisotropy and antisymmetric Dzyaloshinskii–Moriya exchange interaction, with the latter contribution being dominant. It has been established from the angular dependences of the magnetization in three orthorhombic planes that the symmetries of the magnetic and crystal structure are identical. The magnetodielectric properties of the Pb2Fe2Ge2O9 single crystals have been studied at different mutual orientations of the electric and magnetic fields. The most prominent anomalies have been observed in the vicinity of the spin-flop transition in a magnetic field applied along the c axis.

Mossbauer Spectroscopy Study of the Superparamagnetism of Ultrasmall E-Fe2O3 Nanoparticles

Knyazev, Yu. V.; Balaev, D. A.; Kirillov, V. L.; Bayukov, O. A.; Mart'yanov, O. N. Source: JETP LETTERS, 108 (8):527-531; 10.1134/S0021364018200092 OCT 2018

The superparamagnetism of an ensemble of ϵ-Fe2O3 nanoparticles with a mean size of 3.9 nm dispersed in a xerogel SiO2 matrix is studied by the Mössbauer spectroscopy method. It is shown that most nanoparticles at room temperature are in the superparamagnetic (unblocked) state. As the temperature decreases, the progressive blocking of the magnetic moments of the particles occurs, which is manifested in the Mössbauer spectra as the transformation of the quadrupole doublet into a Zeeman sextet. The analysis of the relative intensity of the superparamagnetic (quadrupole doublet) and magnetically split (sextets) spectral components in the range of 4–300 K provides the particle size distribution, which is in agreement with the transmission electron microscopy data. The values of the effective magnetic anisotropy constants (Keff) are determined, and the contribution of surface anisotropy (KS) is estimated for particles of various sizes. It is shown that the quantity Keff is inversely proportional to the particle size, which indicates the significant contribution of the surface to the magnetic state of the ϵ-Fe2O3 nanoparticles with the size of several nanometers.

Magnetodielectric effect in a metamaterial consisting of xerogel with embedded epsilon-Fe2O3 iron oxide nanoparticles

Dubrovskiy, A. A.; Balaev, D. A.; Krasikov, A. A.; Yakushhkin, S. S.; Kirillov, V. L.; Martyanov, O. N. Source: SOLID STATE COMMUNICATIONS, 289 27-29; 10.1016/j.ssc.2018.11.020 FEB 2019

The ε-Fe2O3 iron oxide is a fairly rare polymorphic modification, which only exists in the form of nanoparticles embedded, as a rule, into a silica gel matrix. This magnetically ordered iron oxide, which exhibits a significant room-temperature coercivity, is a ferroelectric; therefore, the magnetoelectric and magnetodielectric properties of this material evoke keen interest. In this work, we investigate the magnetodielectric (MD) effect in a metamaterial consisting of xerogel SiO2 with embedded ε-Fe2O3 nanoparticles 9 nm in size on average in a concentration of 20 mass.%. This bulk material exhibits the MD effect in a wide temperature range. The temperature behavior of the permittivity is related to the magnetic state of the ε-Fe2O3 oxide, which undergoes the magnetic transition from the magnetically hard to magnetically soft phase in the temperature range of 80–150 K, indicating the interplay of the ε-Fe2O3 magnetic and charge subsystems.

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