Magnetism, spintronics

Magneto-optical effects in Zn$_{1-x}$Co$_x$Fe$_2$O$_4$ and Mg$_{1-x}$Co$_x$Fe$_2$O$_4$ mixed ferrite nanoparticles

A. È. Sokolov^ab, I. S. Edelman^a, O. S. Ivanova^ab, R. D. Ivantsov^a, D. A. Petrov^a, Yu. V. Knyazev^ab, A. Thakur^c, P. Thakur<sup>c

a</sup> L. V. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Krasnoyarsk
^b Siberian Federal University, Krasnoyarsk
^c Amity University Haryana, Gurugram, Haryana, India

Abstract: Mixed Zn-Co and Mg-Co ferrite nanoparticles (NPs) with the formulas Zn$_{1-x}$Co$_x$Fe$_2$O$_4$ and Mg$_{1-x}$Co$_x$Fe$_2$O$_4$ where $x$ was equal to 0.0, 0.2, and 0.4 were synthesized via auto- combustion method using citrate precursor as a catalyst that initiates a thermal reaction. X-ray diffraction patterns showed that for all compositions, NPs are nanocrystals of the Fd-3m space group. $^{57}$Fe Moessbauer spectroscopy showed all Co$^{2+}$ ions in Mg-Co ferrite to occupy the octahedral positions only and Fe$^{3+}$ ions to be distributed approximately equally between octahedral and tetrahedral positions. In Zn-Co ferrite NPs, Co$^{2+}$ ions are distributed approximately evenly between these interstitial positions, and Fe$^{3+}$ ions are localized preferably in octahedral positions. Magnetic measurements demonstrate large values of saturation magnetization, Ms, in both cases but high coercivity, $H_c$, in the first case and low coercivity in the second one. Spectra of the Faraday effect and magnetic circular dichroism were obtained for such mixed ferrites for the first time and their dependence on the nature of the non-magnetic ion and cobalt concentration was analyzed. In particular, the analysis carried out allowed us to associate unambiguously the strong peak in the near infrared region with the spin allowed crystal field electron transition in Co$^{2+}$ ions situated in octahedral positions.

Keywords: nanostructure, magnetic properties, Moessbauer effect, magnetic circular dichroism, Faraday effect.

Received: 14.07.2025
Revised: 16.07.2025
Accepted: 17.07.2025

DOI: 10.61011/FTT.2025.08.61323.194-25

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