K. P. Polyakova

Solid-state synthesis of the ZnO-Fe 3 O 4 nanocomposite: Structural and magnetic properties

The structural and magnetic properties of ZnO-Fe3O4 nanocomposites produced by the solid-state reaction Zn + 3Fe2O3 → ZnO + 2Fe3O4 upon annealing of Zn/α-Fe2O3 films under vacuum at a temperature of 450°C have been studied. Ferrimagnetic Fe3O4 clusters with an average grain size of 40 nm and a magnetization of ∼430 emu/cm3 at room temperature, which are surrounded by a ZnO layer with a large contact surface, have been synthesized. The magnetic characteristics of the ZnO-Fe3O4 nanocomposite in the temperature range of 10–300 K have been presented.

Magneto-optical properties of polycrystalline CoCrFeO4 films

A methods of obtaining polycrystalline CoCrFeO4 films based on solid-phase reactions in Cr2O3/Co/Fe layer structures in the regimes of isothermal annealing and self-propagating high-temperature synthesis (SHS) is described. The magneto-optical properties of the obtained films have been studied. It is established that the spectra of magneto-optical characteristics depend on the solid-phase reaction regime and synthesis temperature. The Faraday rotation angle exhibits a local maximum (2θF = 5 deg/μm) at a wave-length of 630 nm.

Evolution of the structure and magneto-optical properties of MnxFe3 − xO4 films prepared by solid-state reactions

This paper reports on the results of investigations into the structure and the magnetic and magnetooptical properties of thin films MnxFe3 − xO4 prepared by solid-state reactions: isothermal annealing, self-propagating high-temperature synthesis, and a combination of these two regimes. The regimes favorable for the formation of films close in composition and structure to the stoichiometric compounds MnFe2O4 or Fe3O4 are established. The features observed in the spectral response of the magneto-optical Faraday effect and of the magnetic circular dichroism of the MnFe2O4 films are considered in terms of the electronic transitions in magnetic ions, primarily Fe3+, which occupy octahedral positions in the spinel structure.

Crystalline texture and magnetic anisotropy of Co-P films prepared by chemical deposition

Chemically deposited Co-P films with a P concentration of 2.5% have been studied by X-ray diffraction (Bragg geometry), electron microscopy, and magnetometry. The films have been found to represent a fine-grained medium in which the orientation of crystallites depends on the film thickness. At a thickness less than 70 nm, the films have a certain crystalline texture with a preferred orientation of the hexagonal axis c of the crystallites perpendicular to the film plane. With increasing film thickness, the character of the texture changes; the c axes of crystallites lie now predominantly in the film plane. At thicknesses exceeding 500 nm, the texture becomes stronger; the c axes are now distributed in the film plane equiprobably. These results can be used when producing magnetic media for longitudinal and transverse magnetic recording.

Magneto-optical properties of nanogranulated Co-Ti-O films

The results from studies of the magneto-optical properties of Co-Ti-O nanogranulated films obtained under conditions of solid-state reaction with oxygen exchange in CoO/Ti layered structures are presented. The magneto-optical spectra of the polar Kerr effect in films with a relative volume of the magnetic fraction of 0.38 to 0.64 has a resonance character in the wavelength range of 450–650 nm. The Kerr rotation angle of the films increases by a factor of 3–5, relative to conventional Co films.

Synthesis and magneto-optical properties of nanogranular Co-Ti-O films

Studies of the structural and magneto-optical properties of nanogranular Co-Ti-O films prepared under conditions of the solid-state reaction with oxygen exchange in the CoO/Ti layered structures are presented. The formation of granular films with compositions near or below the percolation threshold is shown. The specific features of the magneto-optical spectra of the prepared films as compared to the spectra of continuous metallic films are revealed.

Magnetic properties of polycrystalline films of CoCr2O4 and CoFe0.5Cr1.5O4 multiferroics

This paper reports on the first study of the magnetic properties of polycrystalline films of CoCr2O4 and CoFe0.5Cr1.5O4 multiferroics. The study covered, in particular, magnetization reversal curves and temperature dependences of the magnetization at temperatures ranging from 4.2 to 300 K in magnetic fields of up to 10 kOe. It has been shown that the Curie temperature and the pattern of the temperature dependence of the magnetization depend on the cation composition of the multiferroic. The temperature dependence of the magnetization of polycrystalline CoCr2O4 films has revealed an anomaly in the temperature range 10–70 K.

The enhanced magneto-optical Kerr effect in Co/TiO2 multilayer films

Spectral dependences of the polarization plane rotation angle (θk) in the polar Kerr effect in Co/TiO2 multilayer nanocomposite films have been studied in the 400–1000 nm wavelength range. It is established that the sign, magnitude, and shape of the magneto-optical spectrum depend on the dielectric spacer thickness and the number of layers in the structure. The Kerr rotation angle in Co/TiO2 multilayers is significantly greater than that in homogeneous Co films of the same thickness. The angle of rotation of the polarization plane reaches a record high value of 2θk = 7.3° in the Co(5 nm)/TiO2(17 nm) multilayer structure with number of layers n = 8 at a wavelength of 540 nm.

Peculiarities of magnetization reversal in exchange-coupled ferro/ferromagnet NiFe/CoP film structures

The effect of layer thicknesses on the magnetic properties and mechanism of magnetization reversal in exchange-coupled NiFe/CoP film structures has been studied. The process of magnetization reversal was studied by analysis of the magnetic-induction and magneto-optical hysteresis loops. It is established that, as the thicknesses of layers in the NiFe/CoP film structure are increased, the system exhibits a transition from homogeneous magnetization reversal in the structure to exchange spring formation in the soft magnetic layer.

Synthesis and magnetic properties of polycrystalline films of Co x Fe y Cr 3 − x − y O 4 and Cr 2 O 3 /CoFe 2 O 4 multiferroics

Magnetic properties of first obtained polycrystalline films of FeCr2O4, CoCr2O4, and CoFe0.5Cr1.5O4 multiferroics and films of a Cr2O3/CoFe2O4 composite multiferroic have been studied. In particular, magnetization curves and temperature dependences of the magnetic moment of the samples were measured in the temperature range 4.2–300 K in fields of up to 10 kOe. It was shown that the Curie point of a multiferroic depends on its cation composition. It was found that an exchange bias of the hysteresis loop exists in films of the Cr2O3/CoFe2O4 composite multiferroic at temperatures below the Néel point of Cr2O3 (330 K).