Balaev Dmitrii A.

Balaev Dmitrii A.


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




  • 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".


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

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.

Pulsed Field-Induced Magnetization Switching in Antiferromagnetic Ferrihydrite Nanoparticles

Balaev, D. A.; Krasikov, A. A.; Velikanov, D. A.; Popkov, S. I.; Dubynin, N. V.; Stolyar, S. V.; Ladygina, V. P.; Yaroslavtsev, R. N. Source: PHYSICS OF THE SOLID STATE, 60 (10):1973-1978; 10.1134/S1063783418100025 OCT 2018

The dynamic magnetization switching of ferrihydrite nanoparticles has been investigated by a pulsed magnetometer technique in maximum fields Hmax of up to 130 kOe with pulse lengths of 4, 8, and 16 ms. Ferrihydrite exhibits antiferromagnetic ordering and defects cause the uncompensated magnetic moment in nanoparticles; therefore, the behavior typical of magnetic nanoparticles is observed. The dynamic hysteresis loops measured under the above-mentioned conditions show that the use of pulsed fields significantly broadens the temperature region of existence of the magnetic hysteresis and the coercivity can be governed by varying the maximum field and pulse length. This behavior is resulted from the relaxation effects typical of conventional ferro- and ferrimagnetic nanoparticles and the features typical of antiferromagnetic nanoparticles.

Epsilon-Fe2O3 nanoparticles embedded in silica xerogel - Magnetic metamaterial

Yakushkin, S. S.; Balaev, D. A.; Dubrovskiy, A. A.; Semenov, S. V.; Knyazev, Yu. V.; Bayukov, O. A.; Kirillov, V. L.; Ivantsov, R. D.; Edelman, I. S.; Martyanov, O. N. Source: CERAMICS INTERNATIONAL, 44 (15):17852-17857; 10.1016/j.ceramint.2018.06.254 OCT 15 2018

A novel method for synthesizing a new metamaterial based on ε-Fe2O3 nanoparticles immobilized in the xerogel matrix was proposed. Samples with different contents of ε-Fe2O3 nanoparticles dispersed in silica xerogel were synthesized by impregnation of as prepared hydrogel with iron (II) salts with the subsequent calcination. The structure and magnetic properties of the prepared composites were studied by transmission electron microscopy, X-ray diffraction, Mössbauer spectroscopy, and static magnetic measurements. The absence of other iron oxide polymorphs, controllable particle size distribution, and high ε-Fe2O3 nanoparticle concentration in combination with the weak interparticle magnetic interactions ensured the preservation of the unique magnetic properties of individual ε-Fe2O3 nanoparticles and allowed us to obtain a novel metamaterial. The high optical transparency and homogeneity of the prepared composites made it possible to detect the magnetic circular dichroism (MCD) of the magnetic silica xerogel, which is typical of the ε-Fe2O3-based systems.

Bacterial Ferrihydrite Nanoparticles: Preparation, Magnetic Properties, and Application in Medicine

Stolyar, S. V.; Balaev, D. A.; Ladygina, V. P.; Dubrovskiy, A. A.; Krasikov, A. A.; Popkov, S. I.; Bayukov, O. A.; Knyazev, Yu V.; Yaroslavtsev, R. N.; Volochaev, M. N.; Iskhakov, R. S.; Dobretsov, K. G.; Morozov, E. V.; Falaleev, O. V.; Inzhevatkin, E. V.; Kolenchukova, O. A.; Chizhova, I. A. JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31 (8):2297-2304; 10.1007/s10948-018-4700-1 AUG 2018

Nanoparticles of antiferromagnetically ordered materials acquire the uncompensated magnetic moment caused by defects and surface effects. A bright example of such a nano-antiferromagnet is nanoferrihydrite consisting of particles 2–5 nm in size, the magnetic moment of which amounts to hundreds of Bohr magnetons per particle. We present a brief review of the studies on magnetic properties of ferrihydrite produced by bacteria. Special attention is focused on the aspects of possible biomedical applications of this material, i.e., the particle elimination, toxicity, and possible use for targeted drug delivery.

Magnetic Parameters of Separation Products and Impurity Aggregates in Concentrates

Yakubailik, E. K.; Ganzhenko, I. M.; Balaev, A. D.; Butov, P. Yu. Source: JOURNAL OF MINING SCIENCE, 53 (6):1133-1140; 10.1134/S1062739117063233 NOV 2017

The changes in separation performance and magnetic characteristics of separation products is traced along the processing circuit of Abagur concentrator at a laboratory scale in order to determine the limit content of magnetite iron in impurity aggregates in the concentrate. The wet magnetic analysis is carried out in the field of H = 175 kA/m, and the magnetic characteristics are determined in the vibration magnetic detector in the field up to 800 kA/m. The concentrate impurity content is governed by the relative content of barren rock and ore aggregates removable in concentration at the given level of the technology.

Temperature behavior of the magnetoresistance hysteresis in a granular high-temperature superconductor: Magnetic flux compression in the intergrain medium

Semenov, SV; Balaev, DA PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS, 550 19-26; 10.1016/j.physc.2018.04.005 JUL 15 2018

Granular high-temperature superconductors (HTSs) are characterized by the hysteretic behavior of magnetoresistance. This phenomenon is attributed to the effective field in the intergrain medium of a granular HTS. At the grain boundaries, which are, in fact, weak Josephson couplings, the dissipation is observed. The effective field in the intergrain medium is a superposition of the external field and the field induced by magnetic moments of HTS grains. Meanwhile, analysis of the field width of the R(H) magnetoresistance hysteresis ΔH = Hdec  −  Hinc at Hdec = const, where Hinc and Hdec are increasing and decreasing branches of the R(H) hysteretic dependence, shows that the effective field in the intergrain medium exceeds by far both the external field and the field induced by magnetic moments of HTS grains. This situation suggests the magnetic flux compression in the intergrain medium because of the small length of grain boundaries, which amounts to ∼1 nm, i.e., is comparable with the coherence length and corresponds to Josephson tunneling in HTS materials. In this work, using the previously developed approach, we examine experimental data on the magnetoresistance and magnetization hysteresis in the granular YBa2Cu3O7 HTS compound in the range from 77 K to the critical temperature. According to the results obtained, the degree of magnetic flux compression determined by the parameter α in the expression for the effective field Beff(H) = H − 4π M(H) α in the intergrain medium remains constant over the investigated temperature range. All the features of the observed evolution of the R(H) hysteretic dependences are explained well within the proposed approach when the expression for Beff(H) contains the experimental M(H) magnetization data and the parameter α of about 20–25. The latter is indicative of the dominant effect of magnetic flux compression in the intergrain medium on the transport properties of granular HTS materials.

Effect of molecular weight of sodium polyacrylates on the size and morphology of nickel nanoparticles synthesized by the modified polyol method and their magnetic properties

Logutenko, O. A.; Titkov, A. I.; Vorob'yov, A. M.; Balaev, D. A.; Shaikhutdinov, K. A.; Semenov, S. V.; Yukhin, Y. M.; Lyakhov, N. Z. EUROPEAN POLYMER JOURNAL, 99 102-110; 10.1016/j.eurpolymj.2017.12.017 FEB 2018

Nickel nanoparticles were synthesized by the reduction of nickel chloride with hydrazine hydrate in a polyol medium in the presence of sodium polyacrylates (Na-PA) having molecular weights (Mw) of 1200, 5100 and 8000. The size and morphology of the resulting nickel nanoparticles were characterized by X-ray diffraction, scanning and transmission electron microscopy. Polymers having lower Mw values were found to be more efficient in reducing the nickel particle size. A decrease in the polymer concentrations yielded the smaller particles. Magnetic measurements showed that the as-prepared powders are ferromagnetic and their saturation magnetization and coercivity are size-dependent. Compared with bulk nickel, the nanoparticles exhibit an enhanced coercivity which is due to their small size and a decreased saturation magnetization resulted from the surface oxidation of the powder. The synthesis procedure offers a simple approach to preparing nickel nanopowders on a large scale which could be used as magnetic recording materials, including high-density memory storage devices.

Modification of the Structure and Magnetic Properties of Cobalt-Doped Ferrihydrite Nanoparticles Under Heat Treatment

Stolyar, S. V.; Balaev, D. A.; Krasikov, A. A.; Dubrovskiy, A. A.; Yaroslavtsev, R. N.; Bayukov, O. A.; Volochaev, M. N.; Iskhakov, R. S. JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31 (4):1133-1138; 10.1007/s10948-017-4263-6 APR 2018

Nanoparticles of antiferromagnetic materials acquire the magnetic moment due to the surface effects and structural defects. According to the Neel hypothesis, magnetic moment μ P of a particle containing N magnetically active atoms with magnetic moment J can be estimated as μ PJ · N n or μ PV n , where V is the particle volume. Numerous studies of the magnetic properties of ferrihydrite 5Fe2O3⋅9H2O and ferritin revealed a value of n ≈ 1/2 for this material, in which Fe atoms have the octahedral surrounding of anions. We investigate the effect of low-temperature annealing of cobalt-doped ferrihydrite nanoparticles on their average size and magnetic properties. Using the Mössbauer spectroscopy study, we demonstrate that doping with Co makes Fe atoms enter the anion tetrahedra which leads to an increase in the exponent n〉1/2 in the expression μ PJ · N n .

Evolution of the Fe3+ Ion Local Environment During the Phase Transition epsilon-Fe2O3 -> alpha-Fe2O3

Yakushkin, S. S.; Balaev, D. A.; Dubrovskiy, A. A.; Semenov, S. V.; Shaikhutdinov, K. A.; Kazakova, M. A.; Bukhtiyarova, G. A.; Martyanov, O. N.; Bayukov, O. A. JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM, 31 (4):1209-1217; 10.1007/s10948-017-4307-y APR 2018

Evolution of the local environment of Fe3+ ions in deposited Fe2O3/SiO2 nanoparticles formed in samples with different iron contents was investigated in order to establish the conditions for obtaining the stable ε-Fe2O3/SiO2 samples without impurities of other iron oxide polymorphs. Microstructure of the samples with an iron content of up to 16% is studied by high-resolution transmission electron microscopy, X-ray diffraction analysis, and Mössbauer spectroscopy, and their magnetic properties are examined. At iron concentrations below 6%, calcinations of iron-containing precursor nanoparticles in a silica gel matrix lead to the formation of the ε-Fe2O3 iron oxide polymorphic modification without foreign phase impurities, while at the iron concentration in the range of 6–12%, the hematite phase forms in the sample in the fraction of no more than 5%. It is concluded on the basis of the data obtained that the spatial stabilization of iron-containing particles is one of the main factors facilitating the formation of the ε-Fe2O3 phase in a silica gel matrix without other iron oxide polymorphs. It is demonstrated that the increase in the iron content leads to the formation of larger particles in the sample and gradual changes of the Fe3+ ion local environment during the phase transition ε-Fe2O3α-Fe2O3.

Day Plots of Bacterial Magnetite from Sediments of Shira Lake (Khakassia, Russia)

Semenov, SV; Balaev, DA; Shaykhutdinov, KA; Rogozin, DY JOURNAL OF SIBERIAN FEDERAL UNIVERSITY-MATHEMATICS & PHYSICS, 10 (2):252-256; 10.17516/1997-1397-2017-10-2-252-256 2017

Temperature behavior of the antiferromagnetic susceptibility of nanoferrihydrite from the measurements of the magnetization curves in fields of up to 250 kOe

Balaev, D. A.; Popkov, S. I.; Krasikov, A. A.; Balaev, A. D.; Dubrovskiy, A. A.; Stolyar, S. V.; Yaroslavtsev, R. N.; Ladygina, V. P.; Iskhakov, R. S. PHYSICS OF THE SOLID STATE, 59 (10):1940-1946; 10.1134/S1063783417100031 OCT 2017

The cross-breeding problem of the temperature dependence of the antiferromagnetic susceptibility of ferrihydrite nanoparticles is considered. Iron ions Fe3+ in ferrihydrite are ordered antiferromagnetically; however, the existence of defects on the surface and in the bulk of nanoparticles induces a noncompensated magnetic moment that leads to a typical superparamagnetic behavior of ensemble of the nanoparticles with a characteristic blocking temperature. In an unblocked state, magnetization curves of such objects are described as a superposition of the Langevin function and the linear-in-field contribution of the antiferromagnetic “core” of the nanoparticles. According to many studies of the magnetization curves performed on ferrihydrite (and related ferritin) nanoparticles in fields to 60 kOe, dependence χAF(T) decreases as temperature increases, which was related before to the superantiferromagnetism effect. As the magnetic field range increases to 250 kOe, the values of χAF obtained from an analysis of the magnetization curves become lower in magnitude; however, the character of the temperature evolution of χAF is changed: now, dependence χAF(T) is an increasing function. The latter is typical for a system of AF particles with random orientation of the crystallographic axes. To correctly determine the antiferromagnetic susceptibility of AF nanoparticles (at least, ferrihydrite) and to search for effects related to the superantiferromagnetism effect, it is necessary to use in experiments the range of magnetic field significantly higher than that the standard value 60 kOe used in most experiments. The study of the temperature evolution of the magnetization curves shows that the observed crossover is due to the existence of small magnetic moments in the samples.

Anisotropy of the magnetoresistance hysteresis in the granular superconductor Y-Ba-Cu-O at different magnetic-field and transport-current orientations

Balaev, D. A.; Semenov, S. V.; Pochekutov, M. A. JOURNAL OF APPLIED PHYSICS, 122 (12):10.1063/1.4986253 SEP 28 2017

Dissipation in granular high-temperature superconductors (HTSs) during the passage of macroscopic transport current j is mainly determined by carrier tunneling through intergrain boundaries (Josephson junctions). In the presence of external magnetic field H, it is necessary to take into account the significant magnetic flux compression, which can lead to the situation when the effective field Beff in the intergrain boundaries exceeds the external field by an order of magnitude. This is observed as a wide hysteresis of the field dependence of magnetoresistance R(H). In this study, we investigate the R(H) hysteresis evolution in granular 1–2-3 HTSs in different jH orientations. The magnetic flux compression significantly affects the magnetoresistance and its hysteresis for both perpendicular (Hj) and parallel (H ǁ j) orientations. The obtained experimental data on the R(H) hysteresis at the arbitrary angles θ = ∠H, j are explained using the approach developed for describing the magnetoresistance hysteresis in granular HTSs with regard to the magnetic flux compression and the model representations proposed by Daghero et al. [Phys. Rev. B 66(13), 11478 (2002)]. A concept of the effective field in the intergrain medium explains the well-known anisotropy of the magnetotransport properties of granular HTSs.

Magnetic properties of NiO nano particles: Contributions of the antiferromagnetic and ferromagnetic subsystems in different magnetic field ranges up to 250 kOe

Balaev, D. A.; Dubrovskiy, A. A.; Krasikov, A. A.; Popkov, S. I.; Balaev, A. D.; Shaikhutdinov, K. A.; Kirillov, V. L.; Mart'yanov, O. N. PHYSICS OF THE SOLID STATE, 59 (8):1547-1552; Doi: 10.1134/S1063783417080029 AUG 2017

The magnetic properties of antiferromagnetic NiO nanoparticles prepared by thermal decomposition of nickel hydroxocarbonate are investigated. According to the data of magnetization measurements in fields of up to 250 kOe, the magnetic moment linearly grows in strong fields, which is caused by the contribution of the antiferromagnetically ordered nanoparticle core, and the antiferromagnetic susceptibility corresponds to that of bulk polycrystalline NiO. This allowed the antiferromagnetic and ferromagnetic contributions to the total magnetic response of a sample to be quantitatively determined. The latter occurs due to the incomplete spin compensation in an antiferromagnetic nanoparticle caused by defects on its surface. It is demonstrated that to correctly determine the superparamagnetic blocking temperature, it is necessary to take into account the antiferromagnetic susceptibility of the particle core.

Superparamagnetic blocking of an ensemble of magnetite nanoparticles upon interparticle interactions

Balaev, D. A.; Semenov, S. V.; Dubrovskiy, A. A.; Yakushkin, S. S.; Kirillov, V. L.; Martyanov, O. N. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 440 199-202; Doi: 10.1016/j.jmmm.2016.12.046 OCT 15 2017

We report on the effect of interparticle magnetic interactions in an ensemble of superparamagnetic magnetite particles with an average size of ~8.4 nm dispersed in the diamagnetic matrix on the blocking of this ensemble in external magnetic field. The two limit cases are investigated: the case of strongly interacting particles, when the value of magnetic dipole-dipole interaction between particles is comparable with the energy of other interactions in the ensemble (the interparticle distance is similar to the nanoparticle diameter) and the case of almost noninteracting particles distant from each other by about ten particle diameters. We demonstrate that the experimental dependence of the blocking temperature on external field is described well within the model [1], in which the density of particles in a nonmagnetic medium is taken into account and the correlation value depends on external magnetic field. The model for describing the magnetic properties of a disperse nanoparticle ensemble is proposed, which makes corrections related to the particle size and mean dipole-dipole interaction energy for the anisotropy constant. The surface magnetic anisotropy of Fe3O4 particles and parameters of the interparticle coupling are estimated.

Establishing of peak effect in YBCO by Nd substitution

Gokhfeld, D. M.; Semenov, S. V.; Balaev, D. A.; Yakimov, I. S.; Dubrovskiy, A. A.; Terentyev, K. Yu.; Freydman, A. L.; Krasikov, A. A.; Petrov, M. I. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS, 440 127-128; Doi:10.1016/j.jmmm.2016.12.089 OCT 15 2017

Y0.75Nd0.25Ba2Cu3O7−d superconductor has the peak effect with pronounced fishtail feature on magnetization hysteresis. The magnetic field of the peak effect maximum is in ~4 times higher than one of NdBa2Cu3O7−d. The magnetization hysteresis is tilted anticlockwise due to paramagnetic Nd3+ ions occurred on the surface of grains and in the vortex cores.

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