D. N. Merenkov

Exchange anisotropy in polycrystalline FeNi∕FeMn films with hysteresis loop asymmetry

The process of magnetization reversal of a FeNi(50A)∕FeMn(50A) polycrystalline film prepared in a magnetic field has been investigated at temperatures ranging from 25to300K. The external field was oriented in the film plane along the easy or difficult axis of the ferromagnetic layer. In the process of magnetization reversal of the film along the easy axis, strong asymmetry of the hysteresis loop is observed together with an exchange shift. As temperature decreases, the asymmetry becomes more pronounced and the shift increases. The field dependences of the magnetization of the film are symmetric and are not shifted when the external field is applied along the difficult axis. The magnetization reversal process is examined on the basis of a model that takes account of the appearance of high-order exchange anisotropy in polycrystalline films. It is shown that the observed strong asymmetry of the hysteresis loop is associated with the formation of a canted phase and the existence of a metastable state. As the ...

Formation of noncollinear spin configurations during magnetization reversal in multilayered Fe/Si films

Abstract Magnetization reversal processes in Fe/Si multilayered films have been studied by means of the longitudinal magneto-optical Kerr effect at room temperature. The multilayers have been grown by DC sputtering on the single-crystal GaAs substrate. The Kerr effect curves had areas with an invariable or slightly varying rotation and had different remanent rotation value in the zero magnetic field for different directions of the magnetic field in the film plane. The observed features are related to the formation of stable and metastable noncollinear spin configurations. The experimental results are explained in the framework of the theory, which takes into account the competition between the bilinear exchange term on the one hand and the biquadratic exchange or cubic magnetic anisotropy terms on the other hand.

Magnetooptical studies of the H–T phase diagram of an Fe/Si multilayered film

The magnetization reversal of a multilayered Fe/Si film having cubic magnetocrystalline anisotropy is investigated in the temperature interval 25–300 K by magnetooptical methods. It is found that the growth of the biquadratic exchange interaction as the temperature is lowered causes a spontaneous second-order phase transition from a collinear antiferromagnetic state to a noncollinear state. The presence of cubic anisotropy in the film gives rise to spontaneous and magnetic-field-induced first-order phase transitions between noncollinear states. Magnetooptical studies permit constructing the H–T magnetic phase diagram of the multilayered Fe/Si film for an orientation of the external field along the hard magnetization axis [110]. A calculation of the H–T phase diagram in the framework of a model taking into account the bilinear exchange and cubic anisotropy, with constants I1 and K that are assumed to be independent of temperature, and also the biquadratic exchange with a linearly temperature-dependent cons...

Visualization of the antiferromagnetic insulator–ferromagnetic metal phase transition in manganite Nd0.5Sr0.5MnO3

It is found that the first-order phase transition from a nonmetallic antiferromagnetic (AFM) state to a metallic ferromagnetic (FM) state in manganite Nd0.5Sr0.5MnO3 is accompanied by a significant change in the reflectivity of the visible light. This effect is used for visualizing the AFM–FM phase transition in Nd0.5Sr0.5MnO3. The coexistence of AFM and FM phases was observed visually during spontaneous and field-induced AFM–FM transitions. In both cases, the transition occurs through nucleation and expansion of domains of the phase that is favorable from the energy point of view. However, the periodic domain structure of the intermediate magnetic state was not formed during the phase transition. A striped domain structure was formed in the AFM state while the FM phase had a uniform structure.

Rotational magnetocaloric effect in TbAl3(BO3)4

A rotational magnetocaloric effect is predicted in the TbAl3(BO3)4 crystal based on the results of measuring field dependences of magnetization and the temperature dependence of heat capacity. The effect is modeled using the quasi-doublet approximation. Changes to the crystal entropy at constant temperature are determined, as well as at varying temperature under adiabatic conditions. The refrigerant capacity of the crystal is estimated. It is shown that terbium aluminum borate is a promising material for magnetic cooling.

H–T phase diagram of a multilayered Gd/Si/Co film with ferrimagnetic ordering of the layers

The magnetization process of multilayered films [Co(30 A)/Si(5 A)/Gd(75 A)/Si(5 A)]20 having a ferrimagnetic ordering of the magnetic moments of the cobalt and gadolinium layers and a compensation temperature Tcomp≈118 K is studied by magnetometric and magnetooptical methods. A magnetic-field-induced spin-orientation transition from the collinear to the noncollinear state is observed. The transition field is determined and the H–T magnetic phase diagram is constructed for the multilayered ferrimagnet Gd/Si/Co in the temperature interval 5–140 K. The phase diagram is also calculated in the framework of molecular field theory, and satisfactory agreement with the experimental results is obtained. The constant of the antiferromagnetic exchange interaction between the cobalt and gadolinium layers is established.

Antiferromagnetic resonance in crystalline PrFe3(BO3)4

Experimental AFMR studies of crystalline PrFe3(BO3)4 over a wide frequency range of 10–143 GHz at a temperature of 4.2 K have been carried out. The high-frequency properties of praseodymium ferroborate are well described in terms of a model of a two-sublattice antiferromagnet with an “easy axis” anisotropy. An energy gap of 134.3 ± 0.5 GHz is determined and the magnitude of the effective magnetic anisotropy field is estimated to be 1.9 ± 0.1 kOe. An analysis indicates that the spin-orientational phase transition in this compound is a first order transition.

Features of electronic paramagnetic resonance in the ErAl3(BO3)4 single crystal

An additional resonance line was found in the EPR spectrum of the ErAl3(BO3)4 crystal at a temperature of 4.2 K, along with the main line. The appearance of an additional line is associated with the possible formation of magnetic clusters in the crystal.

Magneto-optical properties of terbium iron borate

The Faraday effect induced by an external magnetic field in TbFe₃(BO₃)₄ and TbAl₃(BO₃)₄ borates at a wavelength 633 nm has been investigated. It was found that the terbium subsystem brings the dominant magnetic contribution to the Faraday rotation at low temperatures in borate TbFe₃(BO₃)₄. For both TbFe₃(BO₃)₄ and TbAl₃(BO₃)₄ the magneto-optical coefficients of the terbium subsystem were determined.

Coercive properties of a Gd/Si/Co multilayer film with a compensation point

The temperature dependence of the coercive field Hc is determined for a multilayer [Gd75 A/Si5 A/Co30 A/Si5 A]20 film with ferrimagnetic ordering of the magnetic moments of the cobalt and gadolinium layers. The maximum value of Hc is observed at a temperature of around 118 K, which corresponds to the compensation point of the film. It is established that in the entire interval of temperatures studied, the variation of the coercive field is due to the variation of the spontaneous magnetization.