The magnetic domain structure in low anisotropy epitaxial garnet films

Single-crystal films of (YCa)₃(FeGe)₅O₁₂ garnets were prepared by the liquid phase epitaxial method on the (111) plane of Gd₃Ga₅O₁₂ substrates. These magnetic bubble domain films have comparable uniaxial anisotropy energy, cubic anisotropy energy and demagnetizing energy. A photographic technique was developed to measure the angles of inclination of the domain magnetization vectors with respect to the normal to the sample surface. Without an applied magnetic field these inclination angles were 58° and 122°. A simple stripe domain model was used to provide an explanation of the experimental results. This model can easily be extended for other types of mixed anisotropy cases.     

Rare earth-yttrium iron-gallium garnet epitaxial films for magnetic bubble domain applications

(RE,Y)₃(Fe,Ga)₅O₁₂ garnets, where RE=Eu or Gd, have been developed for use as magnetic bubble domain materials. Magnetic and crystallographic studies were used to find suitable compositions for epitaxial thin films on nonmagnetic garnet substrate crystals. Properties of films grown by liquid phase epitaxy on Czochralski Gd-Ga garnet (111) substrates are discussed. Uniaxial anisotropy in the films can be interpreted as being the result of a lattice mismatch stress mechanism. The Gd-Y films with uniaxial anisotropy are in tension while the Eu-Y films are in compression as shown by lattice spacing differences between films and their substrates. Uncracked, high stability Eu-Y films with very high compressive stresses were grown. Annealing experiments reveal significant changes in anisotropy which correlate with large changes in film lattice spacing. Thus, it is possible to obtain high uniaxial anisotropy in garnets containing only one kind of rare earth ion together with a nonmagnetic ion such as yttrium. These films support domains with very high wall velocities at typical device drive fields.     

Effect of lanthanum on growth-induced anisotropy in LPE bubble garnet films

Growth-induced anisotropy, Ku, in bubble garnet films containing La and Eu or Sm has been found to be anomalous compared to that produced by Eu or Sm and smaller ions such as Y or Lu. In     

Calcium germanium substituted iron garnet films for magnetic bubble applications

Mixed rare earth iron garnet films containing calcium and germanium have been grown on (111) oriented gadolinium gallium garnet (GGG) substrates. The effect of growth conditions on film composition and properties is discussed. The 5 μm diameter bubble films have good magnetic properties; however, temperature control during film growth is very critical.     

The effect of substrate defects on epitaxial magnetic garnet films

The stress patterns associated with various defects in Czochralski-grown gadolinium gallium garnet (GGG) crystals have been observed using a polarizing microscope. The effect of these defects on both the surface topography and the magnetic behaviour of epitaxial magnetic garnet films grown on GGG substrates is reported. In particular, iridium inclusions and defects of a filamentary nature affect the surface topography. Other types of defect influence the magnetic behaviour of the films in a manner attributable to a change in the lattice parameter.     

Control of the anisotropy field of successively grown garnet films

The anisotropy field of magnetic bubble garnet films grown by LPE is an important property to be controlled as well as the bubble collapse field and the strip width. The anisotropy field is comparatively likely to drift with run number even if the characteristic length can be kept constant and directly affects the device operation. In order to suppress the drift of the anisotropy field, the melt compositional drift must be suppressed by the periodic addition of garnet oxides and flux to the melt.     

In-plane magnetic anisotropy and temperature dependence of switching field in (Ga, Mn) as ferromagnetic semiconductors

We explore the magnetic anisotropy of GaMnAs ferromagnetic semiconductor by Planar Hall Effect (PHE) measurements. Using low magnitude of applied magnetic field (i.e., when the magnitude H is smaller than both cubic Hc and uniaxial Hu anisotropy field), we have observed various shapes of applied magnetic field direction dependence of Planar Hall Resistance (PHR). In particular, in two regions of temperature. At T < Tc/2, the "square-shape" signal and at T > Tc/2 the "zigzag-shape" signal of PHR. They reflect different magnetic anisotropy and provide information about magnetization reversal process in GaMnAs ferromagnetic semiconductor. The theoretical model calculation of PHR based on the free energy density reproduces well the experimental data. We report also the temperature dependence of anisotropy constants and magnetization orientations. The transition of easy axis from biaxial to uniaxiale axes has been observed and confirmed by SQUID measurements.     

Temperature dependence of the growth-induced anisotropy of Ge-substituted garnet films by resonance techniques

Ferromagnetic resonance techniques have been used to measure the growth-and stress-induced uniaxial magnetic anisotropy of LPE grown garnet films of the nominal composition Y_1.64Eu_0.10Lu_0.30Ca_0.96Ge_0.96Fe_4.04O₁₂ from 130°K to near the Curie temperature, 455°K. The longitudinal and transverse resonance fields were measured prior and subsequent to an anneal at 1453°K. The growth-induced anisotropy, K^G_u ～?0.03 × 10⁴ ergs/cm³ at 300°K, was found to be approximately 10% of the stress-induced anisotropy, and of opposite sign for these tensile films. The associated anisotropy field, $\text{2}\text{K}{}^{\mathrm{G}}{}_{\mathrm{u}}\text{M}$ exhibited a reversal of slope, with a maximum occurring at 310°K. A model which assumes the existence of a surface anisotropy is proposed to explain these observations. The temperature dependence of the cubic anisotropy, the magnetization, the linewidth, and the exchange constant have been measured also.     

The magnetic anisotropy of thin epitaxial CrO<Subscript>2</Subscript> films studied by ferromagnetic resonance

The magnetic anisotropy of thin epitaxial films of chromium dioxide (CrO₂) has been studied as a function of the film thickness by the ferromagnetic resonance (FMR) technique. CrO₂ films with various thicknesses in the range from 27 to 535 nm have been grown on (100)-oriented TiO₂ substrates by chemical vapor deposition using CrO₃ as a solid precursor. In a series of CrO₂ films grown on the substrates cleaned by etching in a hydrofluoric acid solution, the FMR signal exhibits anisotropy and is strongly dependent on the film thickness. The magnetic properties of CrO₂ films are determined by a competition between the magnetocrystalline and magnetoelastic anisotropy energies, the latter being related to elastic tensile stresses caused by the lattice mismatch between the film and the substrate. In the films of minimum thickness (27 nm), this strain-induced anisotropy is predominant and the easy magnetization axis switches from the [ 001] crystallographic direction (characteristic of the bulk magnet) to the [ 010] direction.     

Intrinsic pinning of a ferromagnetic domain wall in yttrium iron garnet films with strong uniaxial anisotropy

Movements of individual domain walls in a ferromagnetic garnet were studied with angstrom resolution. The measurements reveal that domain walls can be locked between adjacent crystallographic planes and propagate by distinct steps matching the lattice periodicity.     

Control of the growth-induced magnetic anisotropy in ferrimagnetic garnet films grown by liquid-phase epitaxy

The influence of melt composition and growth temperature T_g on the growth-induced magnetic anisotropy constant K^g_u in Bi substituted LPE ferrimagnetic garnet films has been investigated. In films grown from Bi₂O₃ based and from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts the value of K^g_u increased upon decreasing T_g, associated with an increasing incorporation of B1. However, at given Bi content the films grown from Bi₂O₃ based fluxes generally exhibited smaller values of K^g_u than those from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts. The addition of small amounts of Ca²⁺ to the Bi₂O₃ based melts resulted in (Y,Bi)-garnet films changing from n- to p-type electrical conductivity at a minimum value of K^g_u. Additions of Si⁴⁺ to a $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melt reduced the uniaxial magnetic anisotropy of La-YIG-Ga films accompanied by a change from p- to n-type conductivity. Similarly, (Gd,Bi)-garnet films from $\text{PbO}\text{B}{}_2\text{O}{}_3$ based melts changed from n- to p-type conductivity upon decreasing T_g where K^g_u changes sign from negative to positive. From the temperature dependence of the electrical conductivity the electron and hole concentrations in some of these films were estimated suggesting that the sign change of K^g_u in the investigated (Gd,Bi)-garnet films and the minimum of K^g_u in the investigated (Y,Bi)-garnet films and (La,Y)-garnet films occur at donor-acceptor compensation. This experimental evidence led us to conclude that the growth induced magnetic anisotropy may be correlated with the presence of donor and acceptor centers in the garnet structure.     

Single-crystal iron garnet films with increased thermal stability of magnetization and ferromagnetic resonance field

A new method for selecting iron-yttrium garnet (IYG) film compositions is proposed and experimentally verified. Using this approach, it is possible to obtain thick IYG films with high magnetic characteristics.     

Induced magnetic anisotropy and strain in permalloy films deposited under magnetic field

Field induced magnetic-anisotropy is a very important but poorly understood property. There have been many hypotheses on the origin of the phenomenon, e.g. strain, atomic pair ordering, etc., but little experimental evidence exist. This study prepares 100 nm thick Permalloy films having the field-induced-magnetic-anisotropy and carefully measure strains, i.e. interplanar distance of crystallographic (111) planes in various directions, using high power synchrotron radiation and precise Grazing Incidence X-Ray Diffraction method. The result delineates that the field-induced-magnetic-anisotropy has a strong correlation with the strain-anisotropy in the film.     

Laser annealing of gallium-substituted garnet epitaxial films in pressurized oxygen

The effects of laser annealing Ga-substituted EuYIG epitaxial films in still, controlled ambients of air and one to five atmospheres of pure oxygen have been studied. An approximately logarithmic increase in saturation magnetization (4pi M_{s}) and decrease in film magnetic Q factor were observed with increasing oxygen pressure in the annealing ambient. Compared with the most successful previous experiments, annealing at five atmospheres of oxygen displaced nearly twice the fraction of Ga from tetrahedral to octahedral lattice sites. As evidenced by the lack of film damage, the correlation of lattice parameter with the location of the Ga ions and the lack of broadening in the ferromagnetic resonance (FMR) lines, effective annealing temperatures above 1850K were achieved with no significant loss of oxygen from the films. The use of FMR to deduce the extent of film annealing was affirmed through the agreement of independent measurements of4piM_{s}by bubble statics and SQUID magnetometry in films indicated to be homogeneous by FMR.     

Flux-gate magnetic field sensor based on yttrium iron garnet films for magnetocardiography investigations

Technical Physics Letters - A new type of f lux-gate vector magnetometer based on epitaxial yttrium iron garnet films has been developed and constructed for magnetocardiography (MCG)...     

Optical absorption in cobalt-containing epitaxial films of gadolinium gallium garnet

The optical absorption of di-and trivalent cobalt ions embedded in single-crystalline films of gadolinium gallium garnet was observed in the samples grown by liquid-phase epitaxy from supercooled solution melts based on PbO-B₂O₃ and PbO-B₂O₃-GeO₂ systems.     

Automated spatial filtering for rapid characterization of LPE bubble garnet films

An automated spatial filtering apparatus used for characterization of magnetic bubble films with zero field strip widths greater than 1.5μm has been constructed. This apparatus makes measurements of the zero field period and the period in an applied magnetic field. When these two measurements are combined with measured values for the film thickness and the Neél temperature, values for relevant material parameters of the bubble films can be calculated using the Kooy and Enz theory. Details of the spatial filter apparatus, the method used for data analysis, and the accuracy of the method are discussed.     

Uniaxial and cubic anisotropy constants in ion-implanted Sm,Tm,Ga:YIG bubble thin films

The effects of ion implantation into (SmTmY)3(GaFe)5O12garnet thin films have been studied by ferromagnetic resonance. He+ ions were used for implantation with doses ranging from 3 to 4 × 10¹⁵He+/ cm²and implantation energy ranging from 150 to 175 Kev. The uniaxial and cubic anisotropy constants have been studied as a function of temperature from 0°C to 100°C for both as-grown and ion-implanted films. The implantation has effectively changed an easy-axis anisotropy to that of an easy plane in the implanted layers of the films. A cubic anisotropy constant K1with values varying from 4 × 10³to 6 × 10³erg/cm³at room temperature has been observed in these films. The results also indicated that to the first order, the implanted region in the film was essentially magnetically uncoupled from the bulk of the film.     

The measurement of the anisotropy field of cylindrical thin magnetic films

The described method for the anisotropy field measurement uses two fields HLand HT. The deviation of magnetization from the easy direction, and hence also sense signals, are proportional to these fields. The ratio of two integrated sense signals atH_{L} = 0andH_{L} neq 0reaches a certain value (∼ 2.5) with fieldH_{T} = H_{k}. In this way, Hkmay be measured by a device designed for the coercive force measurement.     

Influence of the anisotropy field gradient on the spectra of spin wave resonance in garnet ferrite films

It is established that the spectrum of spin wave (SW) resonance in garnet ferrite films with linear depth profile of the effective anisotropy consists (unlike the spectrum of homogeneous films) of a series of high-intensity SW modes and modes of very low intensity. The distribution of resonance fields of high-intensity SW modes depends on the gradient of the effective anisotropy field. For the same film thickness, the number of these modes increases with the value of gradient.