Drift of domain walls in a harmonic magnetic field

It is shown that a two-step form of the dynamic magnetization curve (and the hysteresis loop) established for a multiaxial ferrite-garnet wafer with a low quality factor (Q < 1) and considerable anisotropy in the plane (K _p /K _u = 14) in the frequency range of 25–1000 Hz is explained by the reconstruction of the dynamic domain structure, particularly by the established features of the drift of domain boundaries in the harmonic magnetic field.     

Dynamic drift of the magnetic domains in ferrite-garnet crystals

The drift of stripe-domain walls in a (111) ferrite-garnet plate with orthorhombic anisotropy and quality factor Q < 1 in an alternating magnetic field of 30–1000 Hz was investigated. The obtained experimental dependences of the domain wall drift velocity on the magnetic field frequency and amplitude are compared to the corresponding theoretical dependences.     

NMR signals from 0° domain-wall magnetic inhomogeneities in cubic ferrite-garnet crystals

The Fe⁵⁷ NMR signals from 0° domain-wall magnetic inhomogeneities are studied numerically at sites where a 180° domain wall is stabilized in cubic ferrite-garnet crystals. The dependence of the NMR absorption lineshape on the induced anisotropy constants and on the magnitude of the constant magnetic field is studied. Fiz. Tverd. Tela (St. Petersburg) 41, 269–273 (February 1999)     

Effect of stabilization processes on NMR signals from 180° domain boundaries in cubic ferrite-garnet crystals

Numerical methods were used to study the effect of stabilization processes on the line shape of NMR signals from 180° domain walls in cubic ferrite-garnet crystals, taking into account the structural change of the boundaries as they shift quasistatically in a magnetic field. The dependences of the amplitude of absorption maxima on the induced anisotropy constants and the amplitude of the external magnetic field are analyzed. Fiz. Tverd. Tela (St. Petersburg) 40, 694–698 (April 1998)     

Photoinduced changes in the dynamic magnetoelastic interaction in yttrium-iron garnet

The effect of light on the excitation efficiency and resonant frequency for the fundamental mode of contour elastic oscillations of a circular ferrite-garnet slab is investigated. A reduction in the dimensionless parameter for the dynamic magnetoelastic coupling is observed. It is shown that illumination produces changes in the effective magnetostriction field and in the magnetic anisotropy. Fiz. Tverd. Tela (St. Petersburg) 39, 1081–1083 (June 1997)     

Study of the fast dynamics of domain walls in ferrite-garnet films in the presence of large in-plane fields

The dynamics of domain walls in ferrite-garnet films with orientation (111) was investigated by twofold digital high-speed photography. The experiments were performed in the presence of an in-plane magnetic field comparable to the anisotropy field of the samples.     

Optical phenomena in bismuth-substituted ferrite-garnet films in external electric field

Magneto-electric properties of bismuth-substituted ferrite-garnet epitaxial films and yttrium ferrite-garnet films have been investigated by using optical polarimetry method, electromagneto-optical (EMO) effect. The EMO effect in the transverse electric (E) field was measured. In the yttrium ferrite-garnet films, the EMO effect in the specified geometry is not registered, though in a longitudinal E-field, it was observed by us. The EMO effect in separate multidomain areas of bismuth-substituted ferrite-garnet films was registered in the transverse electric field. A weak hysteresis appears in the magnetic-field dependences of the measured effect. A value of the EMO signal considerably depends on the external magnetic field, and in the homogeneously magnetized films, the EMO effect is practically absent. The irradiation of bismuth-substituted ferrite-garnet films by powerful laser impulse leads to increase of the EMO signal that can be a result of removal, in them, of nonuniform pressure.     

Coercivity and induced magnetic anisotropy by stress and/or field annealing in Fe- and Co- based (Finemet-type) amorphous alloys

Uniaxial magnetic anisotropy has been induced in amorphous Fe_73.5Cu₁Nb₃Si_15.5B₇ (Fe-rich) and (Co₇₇Si_13.5B_9.5)₉₀Fe₇Nb₃ (Co-rich) ferromagnetic alloys by annealing under stress and/or magnetic field. Such anisotropy plays a crucial role on the magnetization process and, consequently, determine the future applications of these materials. The mechanisms involved on the origin of such induced magnetic anisotropy showed significant differences between Fe-rich and Co-rich amorphous alloys. This work provides a comparative study of the coercive field and induced magnetic anisotropy in Fe-rich and Co-rich (Finemet) amorphous alloys treated by stress and/or field.     

Magnetic properties of nanostructured samples of yttrium iron ferrite-garnet obtained by severe plastic deformation

The magnetic properties of nanoceramics of yttrium iron ferrite-garnet obtained by severe plastic deformation were investigated using the self-excited oscillator method. It is found that the coercive force and anisotropy field increase with an increase in strain and a decrease in the crystallite size.     

Optical anisotropy of Tb3+ ions in a garnet structure

Low-temperature measurements of the absorption spectra of linearly polarized light are performed by Tb³⁺ ions of paramagnetic Tb₃Ga₅O₁₂ and magnetically ordered Tb₃Fe₅O₁₂ crystals in the optical transition domains⁷F₆–⁷F₀,⁷F₆–⁷F₁ in a transverse magnetization geometry. It is shown that at T = 100 K an abrupt anisotropy of the Tb³⁺ ion absorption spectra is observed in a terbium ferrite-garnet depending on the orientation of the magnetization vector I relative to the crystallgraphic axes, where the strongest changes in energetic level structure are noted at 18–25° angles between I and the [110] axis. Reduction of the temperature to 30 K results in isotropization of the spectra, which is associated with a high local anisotropy of the magnetic moment of the terbium ion in the ferrite-garnet structure at low temperatures. Dispersion dependences are obtained for the absorption index and the contribution to the refractive index n' due to the Tb³⁺ optical transitions being examined.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 102–107, March, 1988.In conclusion, the authors are grateful to G. S. Krinchik for stimulation of this research and useful discussions and to A. I. Popov for useful discussion.     

Effect of magnetic field annealing on microstructure and magnetic properties of FePt films

FePt (20 nm) films were annealed in a magnetic field (along the normal direction of the films) at a temperature around the Curie temperature of L1₀ FePt. The influence of magnetic filed annealing on texture and magnetic properties of FePt films were investigated. The results indicate that preferential (0 0 1) orientation and perpendicular anisotropy can be obtained in L1₀ FePt films by using magnetic field annealing around the Curie temperature of L1₀ FePt. This is one of the potential methods to obtain (0 0 1) orientation and thus to improve the perpendicular anisotropy in FePt films.     

Magnetic superconductors of HoMo6S8 type: The effect of magnetic field and supercurrent

We study the magnetic superconductors for which the second order phase transition to the ferro-magnetic state would take place at the temperature θ_c ? T_c1 if the superconductivity was absent. In this case the inhomogeneous magnetic structure of domain-like type (DS phase) appears in superconductors below T_M ≈ θ_c. The effect of the magnetic field H on DS phase is analysed and the region of DS phade existence in the plane (H, T) is found. The new peaks 2nQ (n is integer) should appear in the neutron scattering in the presence of the magnetic field. The wavevector Q of magnetic structure decreases with the growth of magnetic field or supercurrent.     

Influence of the special features of the effective magnetic anisotropy on the temperature dependences of the magnetoimpedance of nanocrystalline Fe<Subscript>73.5</Subscript>Si<Subscript>16.5</Subscript>B<Subscript>6</Subscript>Nb<Subscript>3</Subscript>Cu<Subscript>1</Subscript> strips

The influence of the thermal treatment type on the temperature dependences of the magnetoimpedance of nanocrystalline Fe_73.5Si_16.5B₆Nb₃Cu₁ alloy strips is investigated. The main mechanisms determining the temperature behavior of the magnetoimpedance of strips with induced magnetic anisotropy having various special features are established. The prospects for application of the alloy strips nanocrystallized in the presence of a magnetic field as sensitive elements of temperature sensors and special magnetic field detectors are demonstrated.     

Domain-like magnetic structure in superconductors of ErRh4B4 and HoMo6S8 type

The problem of the coexistence of superconductivity and magnetic order is studied by taking into account the indirect exchange interaction, magnetic dipolar interaction and magnetic anisotropy. It is shown that the domain-like magnetic structure should be realized in the superconducting phases of ErRh₄B₄ and HoMo₆S₈ at the temperatures T_m = 1.4 and 0.7 K respectively. The transition from superconducting domain-like phase (DS) to the normal ferromagnetic (FN) state is described.     

Determination of the in-plane anisotropy field in hexagonal systems via rotational magnetization: Theoretical model and Monte Carlo simulations

The magnetic anisotropy field in thin films with in-plane uniaxial anisotropy can be deduced from the VSM magnetization curves measured in magnetic fields of constant magnitudes. This offers a new possibility of applying rotational magnetization curves to determine the first- and second-order anisotropy constant in these films. In this paper we report a theoretical derivation of rotational magnetization curve in hexagonal crystal system with easy-plane anisotropy based on the principle of the minimum total energy. This model is applied to calculate and analyze the rotational magnetization process for magnetic spherical particles with hexagonal easy-plane anisotropy when rotating the external magnetic field in the basal plane. The theoretical calculations are consistent with Monte Carlo simulation results. It is found that to well reproduce experimental curves, the effect of coercive force on the magnetization reversal process should be fully considered when the intensity of the external field is much weaker than that of the anisotropy field. Our research proves that the rotational magnetization curve from VSM measurement provides an effective access to analyze the in-plane anisotropy constant K ₃ in hexagonal compounds, and the suitable experimental condition to measure K ₃ is met when the ratio of the magnitude of the external field to that of the anisotropy field is around 0.2. Supported by the National Natural Science Foundation of China (Grant Nos. 90505007 and 10774061) Recommended by LI FaShen     

Magnetic anisotropy of strained epitaxial manganite films

The in-plane magnetic anisotropy of epitaxial La_0.7Sr_0.3MnO₃ (LSMO) films is studied at room temperature by the following three independent techniques: magnetooptical Kerr effect, ferromagnetic resonance at a frequency of 9.61 GHz, and recording of absorption spectra of electromagnetic radiation at a frequency of 290.6 MHz. The films are deposited onto NdGaO₃ (NGO) substrates in which the (110)NGO plane is tilted at an angle of 0–25.7° to the substrate plane. The uniaxial magnetic anisotropy induced by the strain of the film is found to increase with the tilt angle of the (110)NGO plane. A model is proposed to describe the change in the magnetic anisotropy energy with the tilt angle. A sharp increase in the radio-frequency absorption in a narrow angular range of a dc magnetic field near a hard magnetization axis is detected The anisotropy parameters of the LSMO films grown on (110)NGO, (001)SrTiO₃, and (001)[(LaAlO₃)_0.3 + (Sr₂AlTaO₆)_0.7] substrates are compared.     

Magnetic anisotropy of the VBO<Subscript>3</Subscript> and CrBO<Subscript>3</Subscript> transition-metal borates

Temperature and field dependences of the magnetization of VBO₃ and CrBO₃ single crystals with the magnetic field applied parallel and perpendicular to the (111) basal plane were measured. VBO₃ was found to have a considerable uniaxial anisotropy with a field H_a≈6.25 T. CrBO₃ was shown to exhibit not only uniaxial but also hexagonal anisotropy. The experimental anisotropy constants were estimated, and their temperature dependences are presented.     

Anisotropy of the upper critical field and specific heat in V3Si — a superconductor with cubic symmetry

The specific heat of a V₃Si single crystal (T _c=17 K, H _c2=20 T) in magnetic fields up to 8 T isinvestigated experimentally for three orientations of the field relative to the crystallographic directions — H∥〈001〉, H∥〈110〉, and H∥〈111〉. Both the upper critical magnetic field and the specific heat of the mixed state are observed to depend on the orientation of the magnetic field relative to the crystallographic directions (anisotropy): The critical field reaches its maximum value and the specific heat its minimum value in a field along the 〈001〉 direction. The anisotropy scale in both phenomena increases as the magnetic field and reaches 3% in a 6 T field. The interrelationship of the upper critical field anisotropy and the specific-heat anisotropy in type-II superconductors is studied. It is shown that the anisotropy of the specific heat in the mixed state in weak fields can serve as a criterion for nontrivial pairing. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 1, 26–29 (10 January 1999)     

Low power light deflector on domain structure in (Y,Ca)3(Fe,Ge)5O12

The domain structures in (Y, Ca)₃(Fe, Ge)₅O₁₂ epitaxial garnet films were investigated as a function of various directions and the intensity of an applied magnetic field. The cubic anisotropy has a strong influence on the domain structure properties in these samples. Very large changes of the stripe domains directions could be obtained by applying a low magnetic field (about 1 [Oe]). The investigated domain structure properties could be used for the light deflectors of a new type, based on the light diffraction.