I. A. Turpanov

Interface effect on the magnetic properties of Ni-Ge bilayer films

Magnetic and magneto-optical properties of the Ni-Ge bilayer films are studied. The unusual temperature behavior of the magnetization curves is revealed: the hysteresis loops at room temperature have a near-rectangular shape; when the films are cooled down to 4.2 K, the coercive force increases by more than an order of magnitude and the asymmetry and displacement of the loop along the field axis are observed. These effects are stronger in thinner Ni layers. The observed features are attributed to the effect of the interlayer between the Ni and Ge layers, which has a complex magnetic structure.

Perpendicular magnetic anisotropy in single-crystal Co50Pt50/MgO(100) films

The crystal structure and hysteretic magnetic properties of equiatomic single-crystal CoPt films applied on MgO substrates by magnetron sputtering, as well as modification of these properties by thermal annealing, are studied. Heat-treated films of thickness in the range 2<d≤16 nm exhibit perpendicular magnetic anisotropy. A correlation between the crystalline anisotropy constant of the CoPt films and the order parameter of the LI0 superstructure in these alloys is found. The effect of a single-crystalline MgO substrate on the structure and magnetic properties of equiatomic CoPt films is revealed.

Self-propagating high-temperature synthesis in Pt/Co/MgO(001) epitaxial thin films

The self-propagating high-temperature synthesis in the two-layer and multilayer Pt/Co(001) thin films has been investigated. It is shown that the initiation of the synthesis occurs at temperatures of 770–820 K. After the synthesis in the two-layer film samples, the PtCo(001) disordered phase exhibits an epitaxial growth at the interface between cobalt and platinum layers. In the multilayer Pt/Co(001) thin films, the self-propagating high-temperature synthesis also brings about the formation of the PtCo(001) disordered phase on the MgO(001) surface. Further annealing at a temperature of 870 K for 4 h results in the transition of the PtCo(001) disordered phase to the ordered phase. Rapid thermal annealing of the Pt/Co(001) multilayer films at a temperature of 1000 K leads to the formation of the CoPt3 phase. The magnetic characteristics change in accord with the structural transformations in Pt/Co film samples.

Effect of alloy formation processes in the Co-Cu system on the magnetic and magnetoresistance properties of multilayer Co/Cu films with ultrathin Co layers prepared by DC magnetron sputtering

This paper reports on a study of multilayer Co/Cu films with an effective thickness of the Co layer of ∼3.5 Å, which were prepared by magnetron sputtering. The samples prepared have been found to have a metastable multiphase structure. An analysis of the data obtained by structural and, primarily, by magnetic methods has revealed that the main phases are the Co/Cu supersaturated solid solution (alloy) with a Co concentration of about 30 at %, the superparamagnetic phase, and the paramagnetic phase, which is accounted for by the presence of small (a few atoms at most) Co clusters embedded in the Cu matrix. A clearly pronounced maximum in the temperature dependences of the low-field magnetoresistance has been found, which is associated with the temperature of the magnetic phase transition of the supersaturated Co-Cu alloy.

Faraday effect in Co/TiO2 films

It is shown that in a layered medium consisting of a magnetic metal (Co) and a nonmagnetic insulator (TiO2), the layer thickness being less than the wavelength of the light, a fundamental change occurs in the character of the Faraday-effect spectra if the number of layers is sufficiently large. When the number of pairs of layers changes from 5 to 10, a maximum appears near ~ 1.7 eV in the Faraday rotation spectrum and the ellipticity passes through zero. The results obtained are compared with the existing theory of the Faraday effect in granular structures consisting of a magnetic metal and nonmagnetic insulator. The surface plasmon energy in thin Co layers is estimated.

Ni-Ge nanostructures: Role of the interface and the magnetic properties

The surface morphology and local structure of layers in the Ni-Ge and Ge-Ni-Ge-Ni-Ge films have been investigated. It has been shown that the surface of the films follows the roughnesses of the substrate surface, which have characteristic dimensions of 2–4 nm in height and ∼100 nm in plane. It has been found that an interface with the depth ranging from 9 to 18 nm is formed at the boundaries between the Ni and Ge layers. The data obtained have been used to explain the specific features of the magnetic properties of the studied films, such as the asymmetry of hysteresis loops at low temperatures and the difference between the temperature dependences of the magnetization of the samples for two cooling modes: in a magnetic field and without a magnetic field.

Kerr rotation and magnetic circular dichroism in Co/SiO2 multilayers

Abstract Kerr rotation and magnetic circular dichroism spectra have been investigated in Co/SiO 2 multilayers in dependence on the dielectric layers thickness. An essential difference has been found between the polar and longitudinal geometries of the experiment. For the polar magnetization of the samples strong changes of the magnetooptical spectra have been observed in comparison with the thick continuous Co film.

Magnetic ordering in multilayer monoatomic Co/Cu films

Abstract The magnetic properties of monoatomic (∼0.3 nm) cobalt layers were studied in multilayer Co/Cu and Co/SiO 2 systems and in a three-layer Cu/Co/Cu film structure. The saturation magnetization M and nuclear spin-spin relaxation times T 2 were measured as functions of the copper layer thickness d Cu . Also the frequency spectra of spin-echo signals from 59 Co nuclei were measured. The main result obtained was experimental evidence for the effect of copper conduction electrons on magnetic ordering in cobalt, which is strongly dependent on d Cu . For d Cu = 0.2–0.3 nm, multilayer structures with monoatomic Co layers exhibit three-dimensional (spatial) properties. As d grows, their properties transform first into quasi-two-dimensional ones, and further into such states when they are probably determined by the quantum size effect for each individual Co layer.

NMR studies of the magnetic state of interfacial cobalt in (Co/Ge)n films

The results of NMR studies of film structures in a cobalt-germanium system as a function of the cobalt layer thickness are presented. Two phases of cobalt, one is a face-centered cubic phase and the other is presumably a Co-Ge alloy with a weakly ferromagnetic order, have been found to exist. A “dead” layer no more than 2 nm in thickness is formed at the interface.

Magnetoresonance properties of three-layer Co/Ge/Co films

Three-layer Co/Ge/Co films have been studied using electron magnetic resonance. It has been established that the resonance spectrum of the film is a superposition of two Lorentzian lines. It has been found that the anisotropy induced at the cobalt‒germanium interface makes the main contribution to the resonance spectrum and determines its features. The temperature dependences of the anisotropy field and the parameters of the interlayer exchange have been measured. The interlayer interactions exhibit an antiferromagnetic character and have been explained in terms of a model similar to the description of superexchange in magnetic dielectrics.