The initial stage in the nonlinear motion of a domain wall in garnet films

A study of the domain-wall motion in single-crystal garnet films of the YBiFeGa system with a perpendicular magnetic anisotropy, activated by a constant in-plane bias field H _p parallel to the wall plane and a pulsed drive field H _g of an amplitude corresponding to the nonlinear region of the domain-wall velocity vs. the H _g relation is reported. The earlier data suggesting the existence of an initial phase of motion, where the wall is accelerated to a high instantaneous velocity, have been confirmed. The wall behavior in the initial phase has been shown to be affected by the field H _p and the drive-field pulse rise time. A possible mechanism of the wall structure transformation after the application of the H _g pulse is considered. It has been established that the dependence of the wall velocity on H _p in the saturation region disagrees with theory.     

Mobility of domain walls in low-loss garnet films

The dependence of the domain wall mobility on the strength of a static magnetic field applied in the plane of the sample is investigated in single-crystal garnet films of the system YBiFeGa with perpendicular magnetic anisotropy and a narrow ferromagnetic resonance line. It is shown that, as in the case of YIG single crystals with cubic magnetic anisotropy, wall motion gives rise to an additional energy loss contribution far greater than the relativistic contribution also present in the case of homogeneous magnetization. It is established that a mechanism recently proposed in theory does not give a correct explanation for this additional contribution, because qualitative as well as quantitative discrepancies exist between the theoretical conclusions and measurement data. Fiz. Tverd. Tela (St. Petersburg) 39, 1253–1256 (July 1997)     

Influence of cubic anisotropy on the temperature characteristics of magnetostatic waves in ferrite films magnetized in the film plane

Expressions for the temperature coefficients of frequency for magnetostatic waves in tangentially magnetized ferrite films having cubic anisotropy are obtained and analyzed. It is shown that in cases where the cubic axis lies in the plane of the film, temperature-induced changes in both the magnitude and direction of the external field can be used for thermostabilization of the frequencies. The problem of two-frequency thermostabilization is considered. The results of experimental investigations of the temperature characteristics of magnetization waves in a tangentially magnetized film of yttrium iron garnet with a {100} surface are presented. Zh. Tekh. Fiz. 68, 99–103 (October 1998)     

Dependence of the domain-wall velocity on the driving field in garnet films

The dependence of the domain-wall velocity on the amplitude of the driving magnetic field pulses is investigated in an iron garnet film of the (YSmCa)₃(FeGe)₅O₁₂ system with a (111) orientation. The results obtained are analyzed from the standpoint of existing theory. A maximum corresponding to the disruption of steady-state motion is observed on the dependence. Thereafter, the velocity at first decreases sharply and then increases. It is theorized that a process involving the periodic generation, propagation, and annihilation of horizontal Bloch lines occurs in the wall in this period. Data are obtained for the velocity saturation region, which confirm a previously proposed empirical formula and a theoretical model, according to which the saturation regime corresponds to a state of chaos. Fiz. Tverd. Tela (St. Petersburg) 39, 660–663 (April 1997)     

Spin-wave resonances in a nonuniform bilayer iron-garnet film

Magnetic resonances are investigated in bilayer Bi-substituted iron garnet films, one layer of which possesses easy-axis and the other easy-plane anisotropy. The behavior of resonances as a function of film thickness, temperature, and annealing is studied. It is shown experimentally that the resonance absorption lines observed in such a nonuniform structure in an external magnetic field oriented perpendicular to the film plane correspond to ferromagnetic (FMR) and spin-wave (SWR) resonances. In addition, the SWR series is excited in the most nonuniform part of the film. A qualitative model explaining the experimental data and making it possible to obtain experimentally the profile of the effective-magnetic-anisotropy field throughout the thickness of the film is proposed. Fiz. Tverd. Tela (St. Petersburg) 41, 1452–1455 (August 1999)     

Dynamics of domain walls in ultrathin magnetic films

The domain walls in ultrathin ferromagnetic films with uniaxial magnetic anisotropy are investigated theoretically. It is shown that taking account of the magnetodipole and magnetoelastic interactions leads to the appearance of an effective anisotropy with respect to the direction of the normal to the plane of the wall. The existence of a new type of domain walls—“corner” walls, at which the magnetization vector is rotated in the plane making a certain angle, which depends on the film parameters, with the plane of the domain wall and the static and dynamic properties of these walls are investigated. The dependence of the limiting velocity of the domain walls on the film thickness is found. Zh. éksp. Teor. Fiz. 112, 1476–1489 (October 1997)     

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)     

Influence of induced uniaxial anisotropy on the domain structure and phase transitions of yttrium-iron garnet films

The effect of induced uniaxial anisotropy on the properties and parameters of the domain structure and phase transitions in yttrium-iron garnet (YIG) films is investigated. Based on the measurements and the derived formulas we determine the difference between the magnetization and the uniaxial anisotropy field for each of the films. We have also measured the parameters of the domain structures and phase transitions of the films for the magnetization parallel and perpendicular to the projections of the [111] crystallographic axes onto the plane of the film. We find that films of pure YIG films grown in (111) are characterized by the existence of some critical value of the uniaxial anisotropy field. It is found that for films in which the uniaxial anisotropy field is larger than this critical value and films in which it is less than this critical value, such parameters of the domain structures as the ratio of the width of the domains to the film thickness, the orientation of the magnetization of the domains, the orientation of the domain boundaries, and the magnitudes of the phase transition fields differ substantially. Fiz. Tverd. Tela (St. Petersburg) 41, 2034–2041 (November 1999)     

Effect of the magnetic field in the plane of a garnet ferrite film with orthorhombic magnetic anisotropy on the dynamics of domain walls

The effect of an in-plane magnetic field on the dependence of the domain-wall velocity on the acting magnetic field is investigated for bismuth-containing garnet ferrite single-crystal films of the composition (Bi,Y,Pr)₃(Fe,Ga)₅O₁₂ with the (210) orientation. The in-plane magnetic field is applied along the 〈120〉 and 〈001〉 crystallographic axes. The domain-wall velocity is measured in directions perpendicular and parallel to the in-plane magnetic field.     

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.     

Structure and properties of deposited yttrium iron garnet films

Ferromagnetic resonance (FMR) and vibrating-sample magnetometer techniques were used to study the nature of the structural characteristics of yttrium iron garnet films deposited through either liquid phase epitaxy or laser evaporation on a (111)-oriented gallium gadolinium garnet substrate. It was proved that, based on the experimentally observed cubic magnetic anisotropy, deposited films should be considered to be single crystals. However, the absence of the FMR domain branch in a nonsaturated film and the shape of the magnetization curve indicate that a deposited film when demagnetized does not have a domain structure, as would be expected for a single-crystal film. According to the model proposed, a deposited film consists of close-packed single-crystal fragments with equal crystallographic orientation, the boundaries between which are in a partially atomically disordered state. As a result, such a film is both locally and macroscopically anisotropic, like a continuous single crystal. This film can split into domains only within a fragment (as is the case in a magnetic granular polycrystal); however, this does not happen, because the linear dimensions of a submicroscopic fragment are smaller than the equilibrium domain width.     

Stripe domain statics in garnet films

Magnetic garnet films grown epitaxially on nonmagnetic garnet substrates exhibit a growth or stress-induced uniaxial anisotropy in addition to the cubic magnetocrystalline anisotropy associated with their crystal symmetry. When the uniaxial anisotropy is dominant over the cubic, such films exhibit stripe or bubble domain structures; even a small cubic anisotropy component can have a decisive effect on the behavior of the domains in applied fields. We report an experimental study of the quadistatic behavior of domains in fields applied to a (111) film in the film plane along (11$\text{2}$) and ($\text{1}$10). The experimental results are interpreted by a new theory that gives good agreement with the observed behavior, and yields an accurate measurement of the cubic and uniaxial anisotropy constants.The main qualitative features of the results are: In a ($\text{1}$10) field, the walls are Neél walls perpendicular to the field. In a (11$\text{2}$) field the walls are Bloch walls parallel to the field, the domain magnetization in adjacent stripes is not symmetrical about the film plane, and adjacent stripes are not of equal width; the domain period first shrinks and then expands with increasing field; and even though the applied field has no component perpendicular to the film plane, the film develops a net perpendicular magnetic moment.     

Dependence of the frequencies of magnetostatic waves on the magnetizing field in ferrite films

Analytical expressions are derived for the derivatives of the frequencies of magnetostatic waves with respect to the external magnetic field in anisotropic ferromagnetic films. Films having cubic anisotropy and 〈100〉, 〈110〉, and 〈111〉 surfaces are analyzed in detail. The frequency-field relations are used in an experimental determination of the temperature coefficients of the cubic anisotropy field and the saturation magnetization in an yttrium iron garnet film. Fiz. Tverd. Tela (St. Petersburg) 40, 2089–2092 (November 1998)     

Effect of magnetocrystalline anisotropy on the temperature characteristics of magnetostatic waves in ferromagnetic films

The temperature dependence of the eigenfrequencies of magnetization oscillation in a single-crystal film is shown to depend strongly on the temperature dependence of the magnetocrystalline anisotropy field. The conditions are considered under which the temperature coefficient of the ferromagnetic resonance frequency in a film with cubic anisotropy changes sign as the orientation of the magnetization vector is changed from the 〈111〉 to the 〈100〉 direction. The spectrum of surface magnetostatic waves is investigated experimentally in 〈110〉-oriented yttrium iron garnet films. It is established that, due to magnetic anisotropy of the ferrite, the temperature dependence of the long-wavelength limit of the frequency spectrum becomes nonmonotonic when a film of this material is magnetized along the 〈100〉 axis.     

Magnetic properties of erbium iron garnet in high magnetic fields up to 150kOe

The magnetic properties of single crystals of erbium iron garnet (ErIG) were studied in applied fields up to 150kOe between 1.4 and 300K. At low temperature, the macroscopic easy direction of the bulk magnetization is [100]; below the compensation temperature (80±2K), the magnetization presents non-linear field evolution. On the assumption of an isolated ground doublet, the anisotropy constantsK _i (i=1,2) of ErIG are given byK _i (Er)+K _i (YIG); theK _i are calculated as a function of theG andg tensor components. It is worthwhile noting that theK _i (Er) are strongly temperature dependent; so at low temperature the anisotropy of the garnet is determined by the rare earth ions, while in the 50 K regionK ₁(Er) becomes comparable toK ₁(YIG) with the opposite sign which results in a very weak anisotropy of the garnet. Above 50 K,K ₁(YIG) is predominant and the Fe³⁺ ions determine the garnet anisotropy.     

Photo-induced domain-wall deformation in YIG:Co films

Experimental study of domain-wall deformation in Co-doped YIG epitaxial films under irradiation by linearly polarized light is reported. A simple theoretical model offering explanation for the observed effects as due to the onset of photo-induced anisotropy in the illuminated volume of the film is proposed. The experimental results are described quantitatively within the model. Fiz. Tverd. Tela (St. Petersburg) 39, 1824–1827 (October 1997)     

High-frequency excitations of stripe-domain lattices in magnetic garnet films

Magnetic garnet films of composition (Y,Bi)₃(Fe,Al)₅O₁₂ have been grown by liquid phase epitaxy on [111] and [110] oriented substrates of gadolinium gallium garnet. The domain wall resonance and the two branches of the domain resonance of periodic stripe domains are measured as function of the bias induction applied in the film plane parallel to the stripes. Resonance frequencies up to 7.5 GHz are observed. An improved version of the hybridization model is developed to describe these resonances. It turns out that hybridization of the domain resonance branches is determined by the cubic anisotropy for [111] oriented films, while for [110] oriented films coupling of the domain resonances is mainly caused by the orthorhombic anisotropy. The theoretical model is in excellent agreement with experiments, no fitting parameters are used. It is also used to derive the phase relation between the precessing magnetizations of neighbouring domains.     

Optical constants of yttrium–iron garnet single-crystal film structures

Light-attenuation spectra of yttrium–iron garnet single-crystal film structures grown on a gallium–gadolinium garnet substrate by liquid-phase epitaxy from the undercooled solution in the melt have been studied and compared with those of bulk yttrium–iron garnet samples. The calculated optical constants are discussed taking into account the influence of crystal field on the splitting of the energy states of iron ions in the film samples. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 218–224, March–April, 2009.     

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)     

Domain-wall dynamics in ferrite garnet films in strong in-plane magnetic fields

The domain-wall dynamics in the ferrite garnet films with the (111) orientation has been investigated by twofold high-speed digital photography in the presence of a magnetic field close in strength to the anisotropy field.