373 ISSN 1068-3755, Surface Engineering and Applied Electrochemistry, 2019, Vol. 55, No. 4, pp. 373–378. © Allerton Press, Inc., 2019. Russian Text © The Author(s), 2019, published in Elektronnaya Obrabotka Materialov, 2019, No. 4, pp. 20–25. Features of the Magnetic Properties of Thin-Film Composites Made with a Solid Solution of the CoGa x Fe 2 – x O 4 and Polyvinylidene Fluoride Sh. M. Hasanli а, *, A. G. Huseynova а , Sh. G. Khalilova а , M. R. Allazov b, **, U. F. Samedova а , and U. M. Safarzade а а Institute of Physics, Azerbaijan National Academy of Sciences, Baku, AZ-1143, Azerbaijan Republic b Baku State University, Baku, Az-1141, Azerbaijan Republic *e-mail: hasanli_sh@rambler.ru **e-mail: allazov_m@mail.ru Received January 26, 2018; revised May 28, 2018; accepted June 13, 2018 Abstract—Thin-film magnetic composite films made using polyvinylidene fluoride (PVDF) and a solid solu- tion of the CoGa x Fe 2– x O 4 type (x = 1.75) were synthesized, and their magnetic characteristics are studied. The dependences of magnetic permeability on the frequency and strength of the alternating field are investi- gated. It is assumed that the reason of the growth of the magnetic permeability due to the magnetic field strength is the displacement of domain boundaries and the orientation of domain moments under the action of an external field, and a sharp decrease in the magnetic permeability versus the frequency of the magnetic field is due to the demagnetizing effect of the eddy currents. Keywords: composite, solid solution, magnetic permeability, ferrite, domains, domain boundaries DOI: 10.3103/S1068375519040045 INTRODUCTION Magnetic materials provide solutions to many technical problems and thus contribute to scientific and technological progress in the modern world. For example, it can be noted that soft and hard magnetic materials are used in electrical and radio engineering, microwave technology, magnetic memory, and many others [1–10]. In addition, we can expect various new magnetic effects to appear at a distance of about the size of an atom up to about ten atomic sizes (about a nanome- ter), due to the fact that the range of exchange interac- tion that leads to magnetic ordering (ferromagnetic or antiferromagnetic) is several interatomic distances. In the last decade, some progress has been made in the development of multilayer magnetic films and artifi- cial magnetic structures, in which new effects appear due to the interaction of the magnetic electron [3] with artificially created nanoscale structures. In accor- dance with the devices developed on these principles, a combination of magnetism and electronics is used, we speak of the creation of a new field of magnetism and technology—magnetoelectronics [8–11]. The aim of this work is to investigate the features of the magnetic parameters of composites based on solid solution crystals of the CoGa x Fe 2– x О 4 type and poly- vinyldene fluoride (PVDF). EXPERIMENTAL, RESULTS AND DISCUSSION For composite manufacture, powders of CoGa 1.75 Fe 0.25 O 4 crystals annealed at Т = 700°С and 1200°С and polyvinyldene fluoride were used as com- ponents. Composites were synthesized from the pow- der mixture of components by hot pressing at Т = 180°С and a pressure of 15 MPa. The content of the composites varied in a wide range of components (25– 45% TV and 75–55% PVDF, respectively). In this paper we discuss the experimental results for a 45% TV–55% PVDF composite. The sample thickness was 180 microns. To measure the electrophysical characteris- tics, contacts of silver paste at a width of 5 mm were applied to the ends of the samples. The dimensions of the composites are 5 × 0.18 × 12 mm 3 . The solid-solution technique is given in [12]. The crystals of the solid solu- tion had a p-type conductivity (σ = 10 –6 Ω m –1 ) and had ferrite ordering up to the Curie temperature ( Т = 600 K). The annealing of CoGa 1.75 Fe 0.25 O 4 was carried out at Т = 700°С and 1200°С for 6 h. Figures 1 and 2 show the diffraction patterns of CoFe 2 O 4 and CoGa 1.75 Fe 0.25 O 4 samples annealed at 500, 700, 1000, and 1200°C. The diffractograms of the powders were taken on a Broker XRDD8 diffractome- ter using CuK α radiation.