ISSN 0027-1349, Moscow University Physics Bulletin, 2024, Vol. 79, No. 5, pp. 616–620. © Allerton Press, Inc., 2024. Russian Text © The Author(s), 2024, published in Vestnik Moskovskogo Universiteta, Seriya 3: Fizika, Astronomiya, 2024, Vol. 79, No. 5, 2450504. CONDENSED MATTER PHYSICS Influence of Annealing on Magneto-Optical Properties of Fe 72.4 Ti 5.4 B 19.2 O 3.0 Nanocrystalline Films N. N. Perova 1* , E. A. Ganshina 1** , I. M. Pripechenkov 1 , D. M. Gridin 1 , E. V. Harin 2 , V. A. Tejetov 2 , E. N. Sheftel 2 , and A. B. Granovsky 1, 3 1 Department of Magnetism, Faculty of Physics, Lomonosov Moscow State University, Moscow, 119991 Russia 2 Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Moscow, 119334 Russia 3 Institute for Theoretical and Applied Electromagnetics, Russian Academy of Sciences, Moscow, 125412 Russia Received May 6, 2024; revised July 8, 2024; accepted July 11, 2024 Abstract—The results of the study on the magnetic properties of Fe 72.4 Ti 5.4 B 19.2 O 3.0 nanocrystalline films, subjected to annealing in vacuum at 200, 300, and 400 ◦ C, are presented. Films with a mixed (nanocrystalline + amorphous) structure, 0.52 μm thick, were obtained by magnetron deposition on glass substrates. Hysteresis loops were measured using a vibrating magnetometer, and the field and spectral dependences of the transverse Kerr effect (TKE) were determined. Magnetization reversal processes were visualized using a magneto-optical Kerr magnetometer. It was shown that the processes of partial crystallization of the initially amorphous phase and the redistribution of Ti and B within crystalline grains and grain boundaries, leading to the formation of new phases as a result of annealing, manifest themselves in a two-stage magnetization reversal process and in the modification of the TKE spectra. Keywords: soft magnetic films, hysteresis loop, transverse Kerr effect, magneto-optical Kerr magnetometer DOI: 10.3103/S0027134924701935 INTRODUCTION Films of Fe-based alloys with nanocrystalline and dispersion-hardened structures, obtained by mag- netron deposition followed by annealing, can exhibit high saturation magnetization, low coercivity, high magnetic permeability up to gigahertz frequencies, and stability [1, 2], making them competitive with the best amorphous-nanocrystalline soft magnetic materials, which are mainly produced in the form of ribbons by melt quenching [3]. The structure and properties of Fe-based films are optimized by varying the conditions and modes of deposition and subse- quent annealing. The magnetic properties of thin film alloys critically depend on the chemical and phase composition of the material, its structure (grain size, microstrain within the grain, interphase boundary structure, etc.), and micromagnetic structure (bulk and surface) [4, 5]. In this work, Fe 72.4 Ti 5.4 B 19.2 O 3.0 films obtained by magnetron deposition were chosen as the model system. Magnetostatic measurements were carried out, and, using a set of magneto-optical * E-mail: perova.n@physics.msu.ru ** E-mail: eagan@mail.ru methods, the bulk and near-surface magnetic prop- erties were studied, which made it possible not only to identify their differences but also to visualize the magnetization reversal process. 1. SAMPLES AND MEASUREMENT TECHNIQUE Samples, in the form of films with a thickness of 0.52 μm on glass substrates, were obtained by mag- netron deposition at MISiS following the technique described in detail in [2]. For comparison, a nanocrys- talline Fe film was also produced. The samples were annealed at temperatures of 200, 300, and 400 ◦ C for 1 h in a vacuum of 2 × 10 −4 Pa. Before annealing, the films were characterized by a mixed structure consisting of nanocrystalline and amorphous phases. The ratio of these phases changes as a result of an- nealing [6]. Hysteresis loops were measured using a Lake Shore 7407 vibrating magnetometer. Three magneto-optical methods were used in the geom- etry of the transverse and longitudinal Kerr effects (TKE/LKE): 1. measurement of field dependences at different wavelengths (TKE); 616