Suppression of the Magnetic Transition in Ultrasmall ϵ-Fe2O3 Nanoparticles: the Size Effect from Nuclear Forward Scattering Data

Knyazev, Y.V., Balaev, D.A., Dubrovskiy, A.A., (...), Kirillov, V.L., Martyanov, O.N.// JETP Letters//

https://doi.org/10.1134/S0021364025606396

The features of the magnetic structure of ultrasmall $ϵ$ -Fe₂O₃ nanoparticles have been studied by the nuclear forward scattering technique using synchrotron radiation. The sample consists of isolated $ϵ$ -Fe₂O₃ nanoparticles with an average size of $⟨ d ⟩ = 3.8$ nm immobilized in a SiO₂ xerogel matrix. The time-domain spectra have been measured in the temperature range of 4–300 K in zero external magnetic field and field $H = 4$ T applied in the longitudinal direction. The character of the change in the hyperfine field H_hf as a function of the external magnetic field is the same in the entire temperature range: unlike large $ϵ$ -Fe₂O₃ particles, a monotonic increase in H_hf is observed in the external field. These results indicate that there is no magnetic transition in the temperature range of 80–150 K for ultrasmall (smaller than $\approx$ 9 nm) $ϵ$ -Fe₂O₃ particles, and the magnetic structure is noncollinear in the range of 4–300 K.