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)     

立方磁晶各向异性对面内磁场中条畴和磁泡稳定性的影响

在八个(111)面磁泡膜上,观察了施加面内(in-plane)磁场后在不同晶轴方向上条状畴的消失过程,测量了条畴消失场H_s^*和磁畴消失场H_k^*与面内磁场的方向的关系。本文计及立方磁晶各向异性,完善了面内磁场中条畴的稳定性理论。用该理论定性地解释了实验结果的主要特点。导出了H_s^*与立方各向异性及面内场方向的两种近似的理论关系,它们分别适用于面内场方向靠近和不十分靠近〈110〉晶轴的情形。它们和实验结果是大致符合的。在〈110〉晶轴上,理论关系具有下列简单的形式:H_k^*<110>=H_s^*<110>=H_k{1+(k₁/2K_u)-[al/h(4πM_s/H_k)²]^2/3},此式与实验结果符合得相当好。 关键词：     

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.     

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.     

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)     

Fast wall encoded magnetic bubbles in (110)-oriented garnet films with orthorhombic anisotropy: Statics

S=OC+ and S=OC-bubbles, which may be of potential interest for information storage, have been identified in several [110]-oriented garnet films with different compositions and material parameters. In all cases these bubbles were found to be stable at zero inplane-fields H_ip. However, when one applies an inplane-field oriented parallel or antiparallel relative to the overall wall magnetization of S=OC±bubbles, their respective static collapse-fields increase or decrease. For a given H_ip collapse-field differences of up to 24 Oe have been measured. Experiments and theoretical calculations clearly evidence that the inplane-field dependent collapse (and stripeout)-data are primarily influenced by the uniaxial and cubic anisotropy constants. Therefore it appears to be possible to tailor the stability range between collapse and stripeout where both bubble types are statically stable and to optimize the discrimination margin with respect to specific device requirements.     

Exchange coupling in ultrathin epitaxial yttrium iron garnet films

Magnetic exchange coupling has been observed for ultrathin films of yttrium iron garnet (Y₃Fe₅O₁₂ or YIG). Single-crystalline YIG films were prepared on yttrium aluminium garnet (Y₃Al₅O₁₂ or YAG) substrates by pulsed laser deposition. (111) and (110) oriented substrates were used. Film thicknesses were varied from 180 ? to 4600 ?. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. Magnetic hysteresis loops recorded for ultrathin YIG films have a “bee-waist” shape and show a coupling between two different magnetic phases. The first phase is magnetically soft YIG. A composition study by secondary ion mass spectroscopy shows the second phase to be Y₃Fe_5-xAl_xO₁₂ due to the interdiffusion of Fe and Al at the film/substrate interface. This compound is known to be magnetically harder and to have weaker magnetization than YIG. The coupling of the two phases leads to a hysteresis loop displacement at low temperatures. This displacement varies differently with film thickness for two substrate orientations. Assuming an interfacial coupling, the maximal interaction energy is estimated to be about 0.17 erg/cm² at 5 K for (111) oriented sample. Received 3 June 2002 / Received in final form 7 October 2002 Published online 27 January 2003 RID="a" ID="a"Presently at LPM, Université H. Poincaré, BP 239, 54506 Vandœuvre-lès-Nancy e-mail: popova@lpm.u-nancy.fr     

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.     

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.     

Magnetostriction of Fe81Ga19 oriented crystals

The effect of the orientation on the magnetostriction in Fe 81 Ga 19 alloy has been investigated experimentally and theoretically.The Fe 81 Ga 19 [001] and [110] oriented crystals were prepared and the magnetostriction was measured under different pre-stress.The saturation magnetostriction of the [001] oriented crystal increases from 170×10-6 to 330×10-6 under the pre-stress from 0 to 50 MPa.The [110] oriented crystal has a saturation magnetostriction from 20×10-6 to 140×10-6 with the compressive pre-stress from 0 to 40 MPa.The magnetostriction of [001] and [110] oriented crystals has been simulated based on the phenomenological theory.The domain rotation path has been determined and the resultant magnetostriction calculated under different pre-stress.The experimental and simulated results both show that the [001] oriented crystal exhibits better magnetostriction than [110] oriented crystal.The enhancement of the saturation magnetostriction by the compressive pre-stress in the [110] oriented crystal is higher than that in the [001] oriented crystal.     

Evaluation of domain wall masses with resonance spectroscopy

Domain wall resonances of different domain configurations occuring in thin garnet films are recorded with a magneto-optic spectrometer under cw excitation. The measured resonance frequencies are used to evaluate the effective domain wall mass density m. The necessary restoring pressure constants are obtained using both experimental and theoretical methods. Generally, m is found to be substantially higher than m_D, the infinite flat wall mass density. We obtain m/m_D between 1.4 and 2.2, with highest values observed for parallel stripes.     

面内场和静态偏磁场作用下条畴和泡畴的稳定性

实验研究面内场H_in和静态偏磁场H_b作用下,(111)面磁泡膜内条畴的消失过程。保持H_b恒定,增加H_in,测量条畴消失场H_s^*和泡畴消失场H_k^*与面内场方向β的变化关系。计及立方磁晶各向异性的影响,建立H_in和H_b共同存在时的条畴稳定性理论。定性解释了实验的主要特点。导出黑、白条畴同时消失时的角度 β_n=1/3(2nπ±arc cos│3/(2^1/2)(M_sH_b)/K₁│)(n=0,±1,±2,…)与实验基本符合。 关键词：     

Iron garnet films with enhanced thermal stability of their magnetic parameters

The ferromagnetic resonance in Y₃Fe_5−x Ga_xO₁₂ (0⩽x⩽0.63), iron garnet films obtained by liquid phase epitaxy on substrates of gadolinium gallium garnet is studied at temperatures of 213–353 K. It is found that in the case of liquid phase epitaxy the distribution coefficient of the gallium in the films varies from 2.2 to 4.0, depending on the composition and growth conditions. It is found that the resonance magnetic fields can be temperature stabilized through temperature-induced changes in the saturation magnetization and anisotropy field. Zh. Tekh. Fiz. 68, 46–50 (September 1998)     

Nanoridge domains in α-phase W films

Two types of nanoridge domains oriented with each other with an angle ranging between 109° and 124° were measured by scanning tunneling microscopy on the α-W film sputter deposited on an oxidized Si surface. Each domain contains nanoridges with a period of 7.5 ± 1.0 nm. No such domains were observed on the β-W film surface. We argued that due to the anisotropy of the W(1 1 0) surface, the impinging W atoms diffuse faster along the 〈111〉 directions on the surface to form the nanoridge structure. There are two equivalent 〈111〉 directions, which give rise to two orientational domains with an angle of ∼110°. An isotropic β-W(1 0 0) phase has no preferred diffusion direction for the impinging W atoms and therefore, no nanoridge domain structure was observed.     

High-frequency susceptibility and ferromagnetic resonance in multidomain thin films of the yttrium-iron garnet type

The field dependence of the high-frequency susceptibility and the ferromagnetic resonance were experimentally studied in a thin (d≈0.1 µm) (111)-oriented single-crystal film of substituted yttrium-iron garnet with the factor q?1. It was shown that the anomaly in the high-frequency susceptibility observed in a magnetic field H parallel to the normal to the film surface in the magnetization saturation region (H≈H_s) has a dual nature; more specifically, this anomaly is associated with an abrupt collapse of the stripe domain structure and a ferromagnetic resonance in the experimental configuration H ∥ [111] and h ⊥ H. In this case, the film transition from the inhomogeneous multidomain state to the homogeneous (single-domain) state at the point H≈H_s has no indications of a second-order phase transition. The experimental frequency-field dependence of ferromagnetic resonance (FMR) in the sample under study, having a characteristic minimum at the point ω₀=5 MHz and H_FMR=H_s, agrees qualitatively and quantitatively with calculations. The influence of the cubic magnetic anisotropy and the film thickness on the FMR spectrum and the orientation of the spontaneous magnetization in domains with respect to the film plane in the zero field H was theoretically studied.     

Magnetic ordering in (110) Eu films in an applied magnetic field

Below its ordering temperature (T _N = 90 K), bulk bcc Eu has a helical magnetic state with propagation vectors along the three equivalent 〈100〉 directions. In contrast, epitaxial (110)Eu films exhibit a unique magnetic ordering: the domain with a magnetic helix propagating along the in-plane [001] direction vanishes on cooling, at the expense of other domains with helices propagating along [100] and [010]. This paper is devoted to the study of the stability of the magnetic domains in an external magnetic field using neutron scattering experiments and macroscopic magnetization measurements. The helix propagating along the [001] direction can be restored by the application of an external field along this direction. On the contrary, when a magnetic field is applied along an intermediate direction, specifically [10], the domain with a helix propagating along [001] is suppressed. Both effects depend on the film thickness. They are explained if one considers that, because of the low magnetic anisotropy of Eu, a helix with a propagation vector parallel to (or close to) the applied magnetic field is energetically more favourable than cycloidal structures with unchanged propagation vectors. Finally, the amplitudes of the propagation vectors and their directions (that are modified in films compared to bulk) do not vary under magnetic field.     

Ge中束缚施主电子的自旋共振及其各向异性线宽

本文利用Ge中浅施主杂质的有效质量波函数,计算了束缚电子的等效自旋哈密顿量,得到在没有外压力及内应力情况下,仅当Ge的导带极值偏离(2π)/α[111]点时,共振频率才是各向导性的。指出通过电子-核双共振实验可能较确切的判断Ge中导带极值的位置。利用畸变势理论及微扰论,计算了在一般缓变的非均匀内应力作用下,共振频率及自旋共振线宽随磁场方向的各向异性变化。最后具体计算了在以拉伸法生长的晶体中和在弯曲的范性形变下,在最主要的位错类型([211]方向刃型及[110]方向螺型位错)应力场作用下自旋共振线宽的非均匀加宽,指出对于不同类型及不同取向的位错有不同的各向异性线宽。与Wilson的实验结果比较,我们得到当位错密度小于10⁴εcm^-2时,位错应力不是形成线宽的主要原因,当磁场在不同的(110)平面内旋转时,线宽将有相似的各向异性。当位错密度大于10⁵εcm^-2时,位错应力对线宽的贡献是主要的。这很容易由实验判断。