Dynamics of domain walls in bismuth-ytterbium-containing garnet ferrite films in the vicinity of the angular momentum compensation point

The dependence of the domain-wall velocity V on the acting magnetic field H is investigated for (Bi,Yb)₃(Fe,Ga)₅O₁₂ garnet ferrite single-crystal films in the vicinity of the angular momentum compensation point at different temperatures. The films are grown by liquid-phase epitaxy from a supercooled solution melt on Cd₃Ga₅O₁₂ substrates with the (111) orientation. It is demonstrated that, in these films, the precessional mechanism is not responsible for the motion of domain walls but there arises an internal effective magnetic field that weakens the acting magnetic field.     

Classical dependence of the domain wall velocity on the magnetic field in garnet ferrite films with orthorhombic magnetic anisotropy

The dependence of the domain wall velocity V on the acting magnetic field H is investigated for bismuth-containing single-crystal garnet ferrite films with orthorhombic magnetic anisotropy. It is shown that this dependence includes both the initial linear portion and a saturation portion and exhibits a complex behavior. This behavior is explained within the model of domain wall motion with spin wave radiation.     

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.     

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.     

On the local magnetization reversal in front of a domain wall moving in a garnet ferrite film with orthorhombic magnetic anisotropy

The experimentally observed shapes of dynamic domains in garnet ferrite single-crystal films with (110) and (210) orientations are explained in terms of in-plane magnetic anisotropy of these films.     

Domain dynamics in (210)-oriented single-crystal (Bi,Y,Lu,Pr)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript> films

Using high-speed photography, dynamic magnetic structures are studied in Bi-containing (210)-oriented single-crystal films of (Bi,Y,Lu,Pr)₃(Fe,Ga)₅O₁₂ grown through liquid-phase epitaxy from an overcooled solution in the melt on (Gd,Ga)₃(Mg,Zr,Ga)₅O₁₂ substrates. At various temperatures, the ranges of pulsed magnetic fields are determined in which unidirectional anisotropy of domain wall velocity and spatial distortions of moving domain walls are observed.     

Influence of an in-plane magnetic field on pulsed magnetization reversal of single-crystal (Bi,Lu)<Subscript>3</Subscript>(Fe,Ga)<Subscript>5</Subscript>O<Subscript>12</Subscript> films with (210) orientation

Photoresponse was used to study the influence of an in-plane magnetic field on pulsed magnetization reversal and relaxation in single-crystal (Bi,Lu)₃(Fe,Ga)₅O₁₂ films with (210) orientation. Dynamic domain structures were observed using high-speed photography.     

基片对交替溅射制备的MnZn铁氧体薄膜结构和磁性的影响

使用成分分别为MnFe₂O₄和ZnFe₂O₄的靶,使用射频溅射交替沉积制备了成分不同的Mn_1-xZn_xFe₂O₄薄膜,沉积薄膜所用基片分别为单晶硅Si（100）,氧化的单晶硅SiO₂/Si（100）, ZnFe₂O₄为衬底的单晶硅ZnFe< 关键词： MnZn铁氧体 纳米晶 软磁性 磁性薄膜     

Unusual characteristics of the spin-wave mechanism of domain-wall motion in iron-garnet films with orthorhombic magnetic anisotropy

The extraordinary dynamic properties of single-crystal iron garnet films with magnetic anisotropy in the plane of the film, specifically unidirectional anisotropy of the domain-wall velocity, are explained on the basis of a mechanism of domain-wall motion that incorporates local rotation of the magnetization vector ahead of the moving domain wall, induced by spin waves radiated from the wall and by anisotropy of the dissipative properties of the single-crystal iron garnet film in its plane. Fiz. Tverd. Tela (St. Petersburg) 39, 1421–1427 (August 1997)     

Layered structure of epitaxial yttrium iron garnet films

The layered structure of yttrium iron garnet films, ranging in thickness from 0.7 to 4.1 μm, grown epitaxially on single-crystal gallium-gadolinium garnet substrates, was investigated by x-ray spectral microanalysis. The ferrite films were chemically etched layer by layer in a mixture of orthophosphoric and sulfuric acids at T=353–423 K. It was established that the chemical composition of the films varies over the thickness because of the nonuniform distribution of gadolinium, gallium, lead, and platinum ions; the film-substrate transitional layer and the surface layer of the film differ most greatly with respect to the composition and magnetic properties. It was shown that the thickness of the transitional layers and their negative effect on the magnetic characteristics of ferrite films decrease appreciably if at the time of immersion of the substrate and pulling of epitaxial structure out of the fluxed solution the substrate holder together with a special mixer rotate at a rate of 50 rpm and the pulling velocity is 20 cm/min. Zh. Tekh. Fiz. 69, 62–64 (December 1999)     

Relaxation under pulsed magnetization reversal of monocrystalline films of (Bi,Lu)3(Fe,Ga)5O12 with (210) orientation

The photoresponse method is used for studying the relaxation process under pulsed magnetization reversal of monocrystalline films with the composition (Bi,Lu)₃(Fe,Ga)₅O₁₂ with (210) orientation depending on the amplitude and duration of the remagnetizing pulse. Magnetization reversal occurs through the formation, motion, and destruction of an end domain wall.     

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)     

A comparative microstructural study of compositionally up- and down-graded (Ba,Sr)TiO3 thin films epitaxially grown on (La,Sr)CoO3-covered MgO(100) substrates by pulsed laser deposition

We report a comparative study of the microstructure of compositionally graded (Ba_1-xSr_x)TiO₃ (BST) films with two compositionally graded directions, up and down, with respect to the substrate, which were deposited epitaxially on (La,Sr)CoO₃ (LSCO)-covered MgO(100) single-crystal substrates by pulsed laser deposition. Cross-sectional transmission electron microscopy (TEM) images and electron diffraction show that the graded films grow epitaxially with their (100) plane parallel to the (100) surface of the MgO single-crystal substrate, and with an in-plane orientation relationship of 〈001〉_BST//〈001〉_LSCO//〈001〉_MgO. The crystalline quality and surface morphology of the graded films are closely related to the direction of the compositional gradient built into the graded films. Down-graded films (starting with a BaTiO₃ layer at the film/substrate interface) have a much better crystalline quality and a smoother surface than the up-graded films (starting with a (Ba_0.75Sr_0.25)TiO₃ layer at the film/substrate interface). Obviously, the BaTiO₃ bottom layer in the down-graded film acts not only as a part of the graded film but also as an excellent seeding layer to enhance the crystallization of the subsequent film layers, resulting in a high crystalline quality of the down-graded film and an enhanced dielectric behavior. Planar (high-resolution) TEM images also demonstrate that down-graded films have a larger, and more uniform, grain size than up-graded films, and that the latter contain voids. PACS 81.15.-z; 77.55.+f; 68.37.Lp; 61.14.-x     

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.     

Nonlinear oscillations of magnetization accompanying pulsed 90°-magnetization of garnet ferrite films with easy-plane anisotropy

Abstract Nonlinear oscillations of magnetization (with a fundamental harmonic frequency of ≈0.5 GHz) emerging during 90°-pulsed magnetization of garnet ferrite films with easy-plane anisotropy are studied. Analysis of longitudinal and transverse magnetization signals and of the magnetization vector hodograph plotted on their basis shows that the weak dependence of the oscillation intensity on duration t _f of the magnetizing magnetic field pulse (upon its variation from 0.4 to 6–8 ns), which is typical of these films, can be explained by the presence of biaxial anisotropy in the plane of actual films.     

Structure and lattice dynamics of heterostructures based on bismuth ferrite and barium strontium titanate on magnesium oxide substrates

Bismuth ferrite films doped with neodymium on MgO single-crystal substrates with an epitaxial barium strontium titanate thin (1–2 nm) sublayer have been prepared by rf sputtering of ceramic targets at an elevated oxygen partial pressure and at temperatures below the ferroelectric and magnetic transition temperatures. It has been revealed using X-ray diffraction and Raman scattering spectroscopy that, in these bismuth ferrite films, a new phase (not observed in bulk samples) is formed. The symmetry of this phase is monoclinic, the unit cell contains two formula units, and the spontaneous polarization vector deviates from the [111]_cub direction and can have different components along the x, y, and z axes.     

Luminescence of gadolinium gallium garnet epitaxial films under excitation by synchrotron radiation

The luminescence excited by synchrotron radiation in gadolinium gallium garnet single-crystal films grown by liquid-phase epitaxy from lead-and bismuth-containing solution melts on Gd₃Ga₅O₁₂ substrates is investigated. It is shown that the luminescence intensity in the visible range of the spectrum depends on the type and concentration of impurity ions passing from the solvent into the film.     

Nature of the low-temperature colossal magnetoresistance of La0.35Nd0.35Sr0.3MnO3 epitaxial films

The colossal negative magnetoresistance (approximately 12%) in a field of 8.4 kOe over a wide range of temperatures below the Curie point T _C ≈240 K in a single-crystal La_0.35Nd_0.35Sr_0.3MnO₃ film on a single-crystal (001)ZrO₂(Y₂O₃) wafer substrate is discussed. Isotherms of the magnetoresistance of this film reveal that its absolute value increases with the field, abruptly in the technical magnetization range and almost linearly in stronger fields. For three single-crystal films of the same composition on (001)LaAlO₃, (001)SrTiO₃, and (001)MgO substrates, colossal magnetoresistance only occurred near T _C ≈240 K and at T<T _C it increased weakly, almost linearly, with the field. In the film on a ZrO₂(Y₂O₃) substrate the electrical resistivity was almost 1.5 orders of magnitude higher than that in the other three films. It is shown that this increase is attributable to the electrical resistance of the interfaces between microregions having four types of crystallographic orientations, while the magnetoresistance in the region before technical saturation of the magnetization is attributable to tunneling of polarized carriers across these interfaces which coincide with the domain walls (in the other three films there is one type of crystallographic orientation). The reduced magnetic moment observed for all four samples, being only 46% of the pure spin value, can be attributed to the existence of magnetically disordered microregions which originate from the large thickness of the domain walls which is greater than the size of the crystallographic microregions and is of the same order as the film thickness. The colossal magnetoresistance near T _C and the low-temperature magnetoresistance in fields exceeding the technical saturation level can be attributed to the existence of strong s-d exchange which is responsible for a steep drop in the carrier mobility (holes) and their partial localization at levels near the top of the valence band. Under the action of the magnetic field the carrier mobility increases and they become delocalized from these levels.     

Ultracold Gases and Quantum Information: Lecture Notes of the Les Houches Summer School in Singapore,edited by C. Miniatura,L-C. Kwek,M. Ducloy,B. Grémaud,B-G. Englert,L.F. Cugliandolo,A. Ekert and K. K. Phua

Measurements of the Faraday magneto-optical effect and of optical absorption in magnetic garnet crystals and films are reviewed. Earlier work was restricted to measurements in the visible spectrum; these measurements showed that the transparency was sufficient to allow magnetic domains to be studied in relatively thick slabs. Within the last year or so interest has been renewed in extending magneto-optical measurements beyond the visible spectrum. In particular, extremely low absorptions are found in the wavelength range of approximately 1–5 microns. Thie work is, in no small way, spurred by the possibility of developing a light-beam modulator using the Faraday effect in this wavelength range. Recent measurements at very short wavelengths using garnet films are also reported. By extending the short wavelength measurements to 3000 Å, about two orders of magnitude increase in Fareday rotation and optical absorption are observed, compared with the visible spectrum measurements.

The Faraday effect has been used to measure magnetic hysteresis loops in single-crystal garnet slabs. Magneto-optical observation of the corresponding domain structures shows them to be particularly simple. Detailed correlation of domain structure and hysteresis loops is described; in addition, an estimate of the domain wall energy and its width is made from these measurements.

The garnets referred to in this review are yttrium iron garnet (YIG), gadolinium iron garnet (GdIG), and YIG doped with gallium (YGaIG).     

Relation between relaxation losses in domain-wall motion and ferromagnetic resonance in garnet films

Domain-wall mobility has been studied in garnet films having perpendicular magnetic anisotropy and a narrow FMR line. An analysis of the obtained and published experimental data shows that for the value of the Landau-Lifshits reduced damping parameter derived from FMR measurements, Λ_FMR>2.4×10⁻⁹ Oe²·s, the domain-wall mobility is inversely proportional to Λ_FMR, which is in agreement with classical theory. For Λ_FMR<2.43×10⁻⁹ Oe²·s, the mobility decreases with decreasing Λ_FMR. Possible reasons for this behavior are discussed. An empirical expression relating the losses entailed in domain motion to FMR-related losses for small Λ_FMR is proposed. Fiz. Tverd. Tela (St. Petersburg) 40, 1519–1525 (August 1998)