G. I. Frolov

Magnetic properties of nanoparticles of 3d metals

The influence of size effects on the coercive force, magnetization, and Curie temperature in nanoparticles of 3d metals is considered. It is shown that experimental results obtained during the last two decades provide new information on peculiar magnetic properties of these particles.

Magnetic interaction between superparamagnetic particles in nanogranular cobalt films

A system of cobalt nanoparticles exhibits a transition from the superparamagnetic state into the state with cooperative magnetic ordering caused by the magnetic interaction between Co particles. It is shown that this transition can be used for obtaining nanogranular materials possessing soft magnetic properties at a large electric resistivity.

Studying the mechanism of exchange coupling in ferro/ferrimagnet NiFe/DyCo film structures

Dependence of the magnetic and magnetooptical properties of an exchange-coupled NiFe/DyCo bilayer system on the thickness (tDyCo) of a magnetically hard layer has been studied. It is established that the unidirectional anisotropy vanishes at tDyCo ∼ 400 Å, while the coercive field in the magnetically soft layer becomes comparable to the exchange-induced field shift. In this case, the DyCo layer magnetization is almost parallel to the film plane, whereas a reference DyCo film exhibits a perpendicular anisotropy. A model of the magnetic state of layers in the ferro/ferrimagnetic layer structure under consideration is proposed, which assumes that a 180° domain wall is formed at the interface upon magnetization reversal in the magnetically soft layer.

Unidirectional anisotropy in ferromagnetic-ferrimagnetic film structures

A mechanism of unidirectional anisotropy formation in an exchange-coupled ferromagnetic-ferrimagnetic film structure with orthogonal effective magnetizations in the layers is investigated. The reason for unidirectional anisotropy is the magnetic heterogeneity of the ferrimagnetic layer in the compensation range. Magnetization reversal in the magnetically soft layer of an (REE–transition metal)/NiFe film structure is discussed based on a model of uniform rotation of magnetization. It is found that unidirectional anisotropy sharply decreases the magnetic noise level in the magnetically soft layer. The field of application of these materials is outlined.

Effects of exchange interaction in bilayer DyxCo1−x/NiFe films in the vicinity of compensation compositions of amorphous DyCo alloys

The displacement field of the hysteresis loop due to exchange anisotropy in planar DyCo/NiFe systems is studied experimentally as a function of the concentration of the rare-earth element. The bilayer DyCo/NiFe film system is characterized by an orthogonal arrangement of the effective magnetizations of separate layers under the condition that the amorphous DyCo layer is prepared in the region of magnetic compensation. An analysis of the dependence of the displacement field on the Dy concentration has led to an understanding of the physical mechanism of the formation of the exchange anisotropy in these planar systems.

Parameters of the transition layer in the exchange-biased NiFe/DyCo film structure

The parameters of the transition layer in exchange-biased film structures are necessary agents to understand the mechanism of formation of unidirectional anisotropy. The layer thickness in NiFe/DyCo films has been determined by comparison of signals of the polar magneto-optical Kerr effect from a reference DyCo film and a hard magnetic layer of the exchange-biased structure. The layer thickness obtained is one order of magnitude larger than that characteristic of ferromagnet-antiferromagnet bilayer films. The mechanism of magnetization reversal of the structure under study has been explained within the model suggesting the formation of 180° boundaries in the interface.

Specific features of unidirectional anisotropy in exchange-coupled DyCo/NiFe film structures

The dependence of the unidirectional anisotropy in a DyCo/NiFe bilayer system on the thickness of the magnetically soft layer has been studied using dynamic and static techniques. The magnitude of the exchange interaction between layers evaluated using the ferromagnetic resonance method is two times that determined from an analysis of the hysteresis loops. It is established that this difference is related to features of the magnetic microstructure of the DyCo layer.

From superparamagnetic to magnetically ordered state in Co-Sm-O nanocrystalline films

Transition of the system of Co nanoparticles from a superparamagnetic state into the region of cooperative magnetic ordering caused by effects of magnetic interaction between particles has been analyzed. The possibility of the preparation of materials with soft magnetic properties and higher electrical resistivity was shown.

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.

Mössbauer studies on TbxFe1−x alloy films with perpendicular magnetic anisotropy

Amorphous ferrimagnetic TbxFe1−x films with perpendicular magnetic anisotropy and TbxFe1−x/NiFe exchange-coupled structures characterized by unidirectional anisotropy are obtained. The magnetic and chemical inhomogeneity of alloys of TbxFe1−x compensation composition is established on the basis of Mössbauer studies of these systems.