Effect of biaxial anisotropy in iron garnet films with in-plane magnetization on the shape of pulsed magnetization reversal curves

The curves of pulsed magnetization reversal in iron garnet films with easy-plane anisotropy are studied. Magnetization reversal is initiated by a pulsed magnetic field aligned with the axis of biaxial anisotropy lying in the plane of the film. The curves exhibit kinks at fields close to the effective field of biaxial anisotropy. Magnetization reversal mechanisms in fields above and below the inflection point are discussed.     

Two-stage magnetization reversal of ferromagnetic films

The two-stage magnetization relaxation of thin ferromagnetic films during the magnetization reversal process is considered in the context of the generalized Kolmogorov three-phasecrystallization model. The experimental data agree qualitatively with the considered model.     

Surface magnetization in semi-infinite ferromagnetic semiconductors with single-ion uniaxial anisotropy

A Green's function technique combined with the transfer-matrix method is used to calculate the surface localized-spin and the conduction-electron magnetization in semi-infinite ferromagnetic semiconductors (FMSs) in the ferromagnetic phase taking into account a single-ion uniaxial anisotropy. The theoretical results were applied to narrow-band as well as to wide-band FMSs.     

Giant magnetocurrent in triple-barrier ferromagnetic resonant-tunneling diode with different magnetization configurations

The authors theoretically investigate a triple-barrier ferromagnetic resonant-tunneling diode composing nonmagnetic couple wells and three GaMnN magnetic barriers, in which two kinds of antiparallel configurations are formed by changing the relative orientation of magnetization in the barriers. Based on a two-band model, the achievement of large magnetocurrents in the resonant bias regime is proposed under an optimal magnetization configuration. The magnetocurrents in both antiparallel configurations of triple-barrier system are much higher than that in double-barrier structure.     

Inhomogeneous magnetostriction states in uniaxial ferromagnetic films

Surface magnetoelastic Love waves and nonuniform distributions of the magnetization and elastic strains are investigated in a uniaxial ferromagnetic film on a massive nonmagnetic substrate in a tangential external magnetic field. A new inhomogeneous phase is predicted having spatial modulation of the order parameter, arising from magnetostrictive coupling of the magnetization with lattice strains near the interface of the magnetoelastic and elastic media. It is shown that, at some critical magnetic field H _c, different from the orientational transition field in an isolated sample, a magnetoelastic Love wave propagating parallel to the magnetization vector in the film plane becomes unstable. The frequency and group velocity of the wave vanish at wave number k=k _c≠0 and the wave freezes, forming a domain structure localized in the film and adjoining substrate. Fiz. Tverd. Tela (St. Petersburg) 41, 665–671 (April 1999)     

Domain morphology in ultrathin ferromagnetic films with perpendicular magnetization

We determine the minimal domain structure for the equilibrium thickness of stripes as well as for the minimal energy of the domain configuration in ultrathin films of ferromagnetically coupled spins, where the easy direction of magnetization is perpendicular to the film. It is found that the equilibrium thickness of stripes and walls depend on the exchange energy. The normalized anisotropy, f, depends on interplay between the magnetic and anisotropy energies and is almost independent of the exchange energy inside the wall. The results are compared with the experimental data for thin Ag/Fe/Ag (0 0 1) films and a good coincidence is obtained between both results.     

Magnetic anisotropy in thin ferromagnetic films

The magnetic properties of thin ferromagnetic films are studied taking into account the magnetic anisotropy term in the Hamiltonian. In the second approximation equations are obtained for the magnetization of the monatomic layers parallel to the surface of the thin film. From these equations one obtains the Curie temperature, which depends on the thickness of the thin film and the ratio a between the anisotropy constant and the exchange energy between two neighbours. A value can be chosen for such that the thin film becomes ferromagnetic only for a thickness greater than a definite value and in this manner the theoretical results can be fitted to the experimental data. The situation in cobalt thin films is dealt with in particular.

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The author extends his thanks to the research workers of CIFA 1 as well as to Dr. L. Valenta for information on the same subject.     

Instantons and solitons in a monolayer film of ferromagnetic grains with biaxial anisotropy

We investigate domain wall and domain structure in a monolyer film consisting of ferromagnetic grains with biaxial anisotropy, which are seen to be the static versions of instanton and soliton, respectively. The equation of motion of the magnetization vector is reduced to the (1 + 2)-dimensional sine-Gordon field equation in strong anisotropy limit and the instanton and soliton configurations are obtained analytically. Various new domain structures in the ferromagnetic film are found.     

Critical magnetization and hysteresis of nanogranular films with perpendicular anisotropy

The magnetic-field dependences of the stability boundaries of the nonequilibrium magnetic states that exist in a nanogranular film with perpendicular anisotropy in tilted magnetic fields are theoretically described, and the corresponding critical magnetization is calculated. The field dependences of the critical magnetization of the film are analyzed at various ratios of the anisotropy field of particles to the maximum possible demagnetizing field of the film. In a tilted magnetic field, the magnetization reversal curves, which include hysteresis loops, are shown to consist of segments of the following three types: equilibrium stable magnetization, nonequilibrium stable magnetization, and critical type of magnetization.     

Magnetic properties of the electroplated Ni-Fe films with a biaxial anisotropy

The main magnetic properties are studied for Ni-Fe films with a biaxiale anisotropy, depending on the angle between the anisotropy axes, establishing that the coupling is positive and it is the stronger, the greater is the angle between the axes.     

Free magnetization oscillations in garnet ferrite films with quasi-planar anisotropy

Free magnetization oscillations in garnet ferrite films with quasi-planar anisotropy was studied. The oscillations were excited by a pulse of an in-plane magnetic field. An analytic expression relating the oscillation frequency to the film parameters and the external magnetic field was derived; the expression is in good agreement with the experimental data. The planar anisotropy is shown to increase the free-oscillation damping.     

Asymmetric kinetics of magnetization reversal of thin exchange-coupled ferromagnetic films

This paper reports on the results of the investigation of the kinetics of magnetization reversal in FeNi-FeMn ferromagnet-antiferromagnet thin hybrid films grown by magnetron sputtering on silicon substrates in the presence of in-plane magnetic field, which provided unidirectional in-plane magnetic anisotropy in the ferromagnetic layer and a single-domain structure of the ferromagnet in the absence of an external magnetic field. The constructed hysteresis loops and magnetization loci have made it possible to reveal the specific features of the magnetization reversal process of an exchange-coupled ferromagnet, to establish new types of asymmetry, and to obtain new proofs for the existence of a spin spring at the ferromagnet-antiferromagnet interface. The visualization of the magnetization reversal process has allowed one to establish a one-to-one correspondence between the macrocharacteristics of the material and the real processes occurring in ferromagnet-antiferromagnet hybrid structures.     

Inhomogeneous configurations in the Lifshitz-type improper incommensurate ferroelectric thin films

The model with the Lifshitz invariant for periodic and helicoidal structures has been analyzed without neglecting of the amplitude function oscillations considering the amplitude and phase functions as equal in significance variables. We have shown that this approach gives significantly richer picture of the order parameter phase and amplitude distribution, than in the approximation of the constant amplitude. The amplitude function oscillations are shown to be extremely important for finding of the phase function distribution in a thin film. Along with numerical calculations, analytic consideration is carried out in the limit of small anisotropy. Both regular and chaotic regimes are studied.     

Characteristic features of ferromagnetic resonance in iron-garnet films with orthorhombic magnetic anisotropy

The characteristic features of ferromagnetic resonance (FMR) were studied in bismuth-containing single-crystal iron-garnet films (BSIGFs) with no rapidly relaxing ions and relatively weak orthorhombic magnetic anisotropy (ORMA). The films were grown on (110) and (210) substrates by liquid-phase epitaxy from a supercooled flux solution. Attention is focused mainly on the unidirectional magnetic anisotropy in the film plane and on the effect of the film/substrate transitional surface layer on the FMR spectrum. Fiz. Tverd. Tela (St. Petersburg) 41, 1254–1258 (July 1999)     

Domain structure and magnetization reversal in thin ferromagnetic elinvar films

A study was made of single-layer Fe-Ni-Cr Elinvar films ranging in thickness from 400 to 10,000 Å and prepared by the thermal sputtering process. For the first time the domain structure of these alloys was examined and found to vary depending on the technological process conditions as well as on the film thickness. The coercive force H is shown here as a function of the specimen thickness, with a maximum value H = 32 Oe in a 640 Å film. The hysteresis loop of Elinvar films has uniaxial anisotropy.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 114–117, November, 1971.     

On the effective magnetization and uniaxial anisotropy of permalloy films

The values of the effective magnetization and uniaxial induced anisotropy were measured on permalloy films, vacuum deposited on unheated glass slides, by the method of local ferromagnetic resonance. The double resonance curves of these films indicate the existence of two magnetically different components; to both components there correspond different values of the effective magnetization and uniaxial anisotropy. These quantities have different local and time variations for each component. The results of measurement agree with the recently proposed model of the stratification of thin ferromagnetic films.The authors thank J. Kaczér and F. Kroupa for valuable discussions.