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)     

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)     

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)     

晶格失配应力对单晶(BiTm)_3(GaFe)_5O_(12)膜磁畴结构的影响

利用液相外延工艺在钆镓石榴石衬底上制得了单晶(BiTm)_3(GaFe)_5O_(12)膜,研究了晶格失配应力对其磁畴结构的影响.研究发现,生长速率越快,膜的晶格常数越大;晶格失配应力可以在一定范围内调整膜的垂直各向异性;随着晶格失配应力由较大张应力逐渐转变为较大压应力,磁畴形状先由磁泡畴转变成迷宫畴,然后转变为过渡态部分弯曲的条状畴,最终转变为整齐排列的条状畴;失配应力同时对畴宽也有影响,膜受到的失配应力越大,畴宽越大.这一实验研究对基于控制晶格失配应力来调控单晶膜的各向异性和磁畴结构有指导意义.     

Width of the ferromagnetic resonance line in an anisotropic magnet in misoriented resonance and scanning magnetic fields

The dependence of the width ΔH_β of the ferromagnetic resonance (FMR) line in anisotropic magnets on the angle of misorientation β between the static (resonance) and scanning magnetic fields was investigated both experimentally and theoretically. The change in the linewidth is due to the dependence of the equilibrium orientation of the magnetization vector on the direction of the magnetic field upon the passage through the resonance. Using iron garnet films as an example, it was shown that under such a misorientation (a nonzero angle β) the linewidth is smallest. It was also shown that a two-dimensional representation of FMR spectra, in contrast to one-dimensional angular dependences of the resonance parameters, contains full information on the spectral characteristics of the film, including noncollinear field configurations.     

Transition of magnetic anisotropy in Ni/GaAs (0 0 1) observed by magnetization and ferromagnetic resonance

Polycrystalline thin Ni films deposited onto GaAs (0 0 1) show a transition of the magnetic anisotropy depending on its thickness. The anisotropy is perpendicular to the film plane for the thicknesses of the film ⩽12 nm. This becomes in-plane in the films having thicknesses ⩾15 nm. The films are deposited onto the n-type GaAs (0 0 1) substrate by the usual thermal evaporation method and also by the electron beam evaporation in ultra high vacuum onto a GaAs epilayer in the standard molecular beam epitaxy system. The magnetization and ferromagnetic resonance (FMR) are observed in the temperature range from 4.2 to 300 K. For the discussion of the microscopic origin of the anomalous properties in magnetization and FMR experiments, the experimental results are reviewed by introducing a uniaxial anisotropy, which is calculated from the easy-axis and hard-axis magnetization data. This calculated anisotropy is able to explain the temperature and angle dependency of the FMR spectra of the Ni films. Hence the magnetization and FMR spectra are in agreement with the type of the anisotropy and its temperature dependency. In addition to these, the temperature dependence of the in-plane magnetic anisotropy is able to explain the previously reported anomalous effect of reducing the squareness at low temperatures in Ni/GaAs.     

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).     

垂直各向异性Ho3Fe5O12薄膜的外延生长与其异质结构的自旋输运

垂直磁各向异性稀土-铁-石榴石纳米薄膜在自旋电子学中具有重要应用前景.本文使用溅射方法在(111)取向掺杂钇钪的钆镓石榴石(Gd_0.63Y_2.37Sc₂Ga₃O₁₂,GYSGG)单晶衬底上外延生长了2—100 nm厚的钬铁石榴石(Ho₃Fe₅O₁₂,HoIG)薄膜,并进一步在HoIG上沉积了3 nm Pt薄膜.测量了室温下HoIG的磁各向异性和HoIG/Pt异质结构的自旋相关输运性质.结果显示,厚度薄至2 nm的HoIG薄膜(小于2个单胞层)在室温仍具有铁磁性,且由于外延应变,2—60 nm厚HoIG薄膜都具有很强的垂直磁各向异性,有效垂直各向异性场最大达350 mT;异质结构样品表现出非常可观的反常霍尔效应和“自旋霍尔/各向异性”磁电阻效应,前者在HoIG厚度小于4 nm时开始缓慢下降,而后者当HoIG厚度小于7 nm时急剧减小,说明相较于反常霍尔效应,磁电阻效应对HoIG的体磁性相对更加敏感;此外,自旋相关热电压随HoIG厚度减薄在整个厚度范围以指数方式下降,说明遵从热激化磁振子运动规律的自旋塞贝克效应是其主要贡献者.本文结果表明HoIG纳米薄膜具有可调控的垂直磁各向异性,厚度大于4 nm的HoIG/Pt异质结构具有高效的自旋界面交换作用,是自旋电子学应用发展的一个重要候选材料.     

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)     

On the velocity of an end domain wall in (Bi,Lu)3(Fe,Ga)5O12 single-crystal films with (210) orientation

The mobility of an end domain wall in (Bi,Lu)₃(Fe,Ga)₅O₁₂ single-crystal garnet ferrite films with (210) orientation is determined by the photoresponse method. It is shown that the mobility of end domain walls in these films is considerably higher than that in (111) single-crystal garnet ferrite films free of rapidly relaxing ions.     

Dynamic range of materials for the magneto-optic imaging of magnetic fields

The range of rearrangement of the natural domain structure of epitaxial garnet ferrite films in magnetic fields produced by conventional recording magnetic media was calculated using numerical methods. Maximum and minimum periods of the recording medium signalograms that could be imaged using the fillm domain rearrangement were obtained as functions of the recording medium and film parameters.     

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     

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.     

Mǒsbauer study of the field induced uniaxial anisotropy in electro-deposited FeCo alloy films

Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability.The paper reports a Mo¨ssbauer study of the field induced in-plane uniaxial anisotropy in electro-deposited FeCo alloy films.The FeCo alloy films were prepared by the electro-deposition method with and without an external magnetic field applied parallel to the film plane during deposition.Vibrating sample magnetometry and Mo¨ssbauer spectroscopy measurements at room temperature indicate that the film deposited in external field shows an in-plane uniaxial anisotropy with an easy direction coinciding with the external field direction and a hard direction perpendicular to the field direction,whereas the film deposited without external field does not show any in-plane anisotropy.Mo¨ssbauer spectra taken in three geometric arrangements show that the magnetic moments are almost constrained in the film plane for the film deposited with applied magnetic field.Also,the magnetic moments tend to align in the direction of the applied external magnetic field during deposition,indicating that the observed anisotropy should be attributed to directional ordering of atomic pairs.     

FMR Investigation of the Magnetic Anisotropy in Films Synthesized by Co<Superscript>+</Superscript> Implantation into Si

Thin ferromagnetic films with the uniaxial magnetic anisotropy were synthesized by Co⁺ implantation into single-crystal silicon in the magnetic field. It was concluded that the formation of the induced magnetic anisotropy is due to the directional atomic pair ordering (Neel–Taniguchi model). The synthesized films were studied by the ferromagnetic resonance (FMR) method in the temperature range from 100 to 300 K. The FMR linewidth is almost independent of temperature, which is in agreement with the Raikher model describing the magnetic resonance of uniaxial magnetic particles. It is found that the temperature dependence of the anisotropy constant is linear. This dependence can be associated with the difference in the coefficients of thermal expansion of the Si (111) substrate and the ion-beam-synthesized cobalt silicide films.     

Spin dynamics at low microwave frequencies in crystalline Fe ultrathin film double layers using co-planar transmission lines

Magnetic damping has been studied in magnetic double layers using a network analyzer (NA) with a coplanar transmission line. The magnetic films consisted of ultrathin crystalline films of Fe separated by an Au spacer. The films were deposited on GaAs(0 0 1) substrates using the molecular beam epitaxy (MBE) technique. NA-ferromagnetic resonance (NA-FMR) measurements were carried out along the magnetic hard axis, allowing one to follow the frequency FMR linewidth down to the 1 GHz range of frequencies. It will be shown that the FMR linewidth in the NA-FMR measurements is not entirely described by Gilbert damping. The additional contribution in the frequency linewidth increases with decreasing frequency, and is most likely caused by dipolar fields associated with an inhomogeneous RF field around the coplanar transmission line.     

On the domain ferromagnetic resonance in bubble lattice exposed to the in-plane field

The domain ferromagnetic resonance (DFMR) of a bubble lattice was measured on garnet films magnetized in the film plane. More than three theoretically predicted DFMR modes were observed as before on magnetoplumbite platelets in the same measurement configuration. The forms of the dispersion curves (frequency/field graphs) of these modes were found to be similar for both materials. The strongly different magnetic parameters of both sample types enabled us to obtain new information about the character of the excited modes. Due to a good optical transparency and high magnetooptical contrast of the garnet films the dispersion of the DFMR modes could be correlated with the actual domain structure.I wish to express my thanks to A. Kolodrubec for the help with microwave measurements and to V. Kamberský and R. Gemperle for a useful discussion.     

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.     

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.     

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.