V. O. Vas’kovskiy

Fe20Ni80/Fe50Mn50 film magnetoresistive medium

The influence of several physico-technological factors on the microstructure and the magnetic and magnetoresistive properties of film structures based on Fe20Ni80/Fe50Mn50 bilayers with exchange (magnetic) bias is investigated. The dependences of the magnetic bias, coercive force, and anisotropic magnetoresistance on the deposition sequence and thickness of layers in the structures, substrate temperature, annealing temperature, and measurement temperature are determined for films obtained by magnetron sputtering, including with a high-frequency electric bias applied to the substrate. It is shown that the film SiO2/Ta(5)/Fe20Ni80(5)/Fe50Mn50(20)/Fe20Ni80(40)/Ta(5) structure offers an optimal combination of properties as a magnetoresistive medium with internal magnetic bias. Testing data for magnetic sensors made of this material by optical lithography are presented.

Effect of phase separation in an Fe20Ni80/Fe50Mn50 structure with exchange coupling

The effect of heat treatment and partial oxidation of an Fe50Mn50 layer on the structure and magnetic properties of exchange-coupled Fe20Ni80/Fe50Mn50 layers has been investigated. The behavior of the exchange-bias field and coercive force depending on the temperature of annealing upon heat treatment in a vacuum or in an oxygen-containing gas mixture has been studied. It has been shown that, by adjusting the parameters of annealing in the gas mixture, it is possible to increase the field of switching of the exchange-coupled Fe20Ni80/Fe50Mn50 layers.

Effect of annealing on the magnetic anisotropy and hysteretic properties of film structures containing Tb-Co amorphous layers

The effect of heat treatment on the magnetic properties of Tb-Co amorphous films and film structures based on them has been studied. Regularities of variations of the coercive force and induced magnetic anisotropy constants of Tb-Co amorphous films and the coercive force and unidirectional anisotropy field of the permalloy layer in Fe19Ni81/Tb-Co films were determined as functions of the annealing temperature. The regularities found have been interpreted by assuming temperature-induced changes in the shortrange atomic order in the amorphous structure and interlayer diffusion in two-layer films.

Influence of the Size and Structural Factors on the Magnetism of Multilayer Films Based on 3d and 4f Metals

This work has presented some data on the layer structuring of films of 3d and 4f metals and their alloys, which have potential for practical use in magnetic sensors. The decrease in the thickness of magnetic layers with this structuring entails natural worsening of the crystallinity and leads to a degradation of magnetic ordering. However, the manifestation of these tendencies depends to a great extent on the conditions of preparation, the composition, and the sequence of the deposition of the contacting layers in the multilayer structures. The combination of these factors makes it possible to realize an optimum composition and optimum structural states of the films, which in a number of cases lead to the appearance of new combinations of functional properties.

Antidot patterned single and bilayer thin films based on ferrimagnetic Tb–Co alloy with perpendicular magnetic anisotropy

Hysteresis properties and magnetization reversal in TbCo(30 nm) and FeNi(10 nm)/TbCo(30 nm) films with nanoscale antidot lattices are investigated to test the effect of nanoholes on the perpendicular anisotropy in the TbCo layer and the induced exchange bias in the FeNi layer. The antidots are introduced by depositing the films on top of hexagonally ordered porous anodic alumina substrates with pore diameter and interpore distance fixed to 75 nm and 105 nm, respectively. The analysis of combined vibrating sample magnetometry, Kerr microscopy and magnetic force microscopy imaging measurements has allowed us to link macroscopic and local magnetization reversal processes. For magnetically hard TbCo films, we demonstrate the tunability of magnetic anisotropy and coercive field (i.e., it increases from 0.2 T for the continuous film to 0.5 T for the antidot film). For the antidot FeNi/TbCo film, magnetization of FeNi is confirmed to be in plane. Although an exchange bias has been locally detected in the FeNi layer, the integrated hysteresis loop has increased coercivity and zero shift along the field axis due to the significantly decreased magnetic anisotropy of TbCo layer.

Specific features of the formation of atomic magnetic moments in amorphous films RE-Co (RE = La, Gd, Tb)

A systematic investigation of the magnetic properties of amorphous films in (RE)xCo100 − x binary systems in the ground state with rare-earth elements (RE) of different types has been performed. The concentration dependences of the average atomic magnetic moments of cobalt (mCo), gadolinium (mGd), and terbium (mTb) have been determined from the analysis of the spontaneous magnetization of the films with a nonmagnetic rare-earth element (La), a rare-earth element with a spherical electron shell (Gd), and a rareearth element with a large orbital magnetic moment (Tb). It has been shown that, in the range 0 < x < 50 at %, the magnetic moment mCo decreases from 1.7 μB to zero, the magnetic moment mGd remains unchanged and almost coincides with the magnetic moment of the free atom (7 μB), and the value of mTb decreases monotonically, but the rate of decrease depends on the method of the sample preparation. The revealed regularities are associated with the concentration change in the electronic structure of cobalt and with the specificity of the magnetic structure of the films, which has a ferromagnetic, ferrimagnetic, or sperimagnetic character for samples containing La, Gd, or Tb, respectively.

Effect of temperature on magnetization reversal characteristics of ferromagnetic 3d metal layers within exchange-coupled FeMn-based structures

Multilayer films Fe20Ni80/FeMn/FM (with FM = Ni, Fe11Ni89, Fe20Ni80, Co30Ni70, Fe, Co) have been prepared and their structure has been estimated. Their hysteretic properties and interlayer coupling parameters have been studied in a temperature range of 5–350 K. Regularities of the magnetization reversal of ferromagnetic layers under magnetic exchange-bias conditions have been interpreted.

Hysteretic properties of nanostructured terbium films

The hysteretic properties of terbium films subjected to layered structuring by introducing nonmagnetic Ti and Si layers of a fixed thickness (2 nm) are studied in the temperature range 2–230 K. It is found that the variation of the Tb layer thickness in the range 1.5–360 nm and the nonmagnetic layer material leads to substantial changes in the magnetic hysteresis of the films and its temperature behavior. These changes are related to a change in the structural composition of the films, which consists of nanocrystalline, granulated, and amorphous Tb phases.

The Features of the Structure and Magnetic Properties of Co-SiO2, Co-Al2O3 Composite Films with Tunneling Magnetoresistance Effect

In the present work, we have studied the structural, magnetic and magnetoresistive properties of Cox(SiO2)100-x and Cox(Al2O3)100-x composite thin films, obtained by magnetron co-sputtering of metallic and insulator targets. It was shown by transmission electron microscopy and by temperature and field dependences of the magnetization that the films have a fine granular structure. For a wide range of compositions an adequate description was possible in frame of the model of homogeneous non-interacting superparamagnetic hexagonal lattice Co particles. Magnetoresistive sensor prototypes were designed on the base of an optimized magnetoresistive Co50(Al2O3)50 composite films

Effect of Granular Spacer on the Exchange Bias Effect in FeMn-Based Film Structures

Abstract —The article deals with a study of interactions between permalloy layers separated by granular Со‒Al2O3 spacer. Multilayer Ta/FeNi/FeMn/FeNi/Co–Al2O3/FeNi/Ta films prepared by magnetron sputtering are the test object. The spacer thickness and content of metallic phase in the spacer have been varied from 0 to 8 nm and 0 to 40%, respectively. A correlation has been found between the Co concentration in the spacer and critical spacer thickness. When the thickness of the spacer exceeds a critical value, the independent magnetization reversal of the permalloy layers adjacent the spacer takes place. It has been shown that, in the case of both cooperative and independent magnetization reversal of permalloy layers, the presence of a spacer substantially affects the hysteretic properties of film structure. The data obtained can be useful when purposefully controlling the coercive force and exchange-bias field in film structures with the unidirectional anisotropy.