Yasuharu Hidaka

Determination of magnetic anisotropy constants for bubble garnet epitaxial films using field orientation dependence in ferromagnetic resonances

Abstract Cubic magnetocrystalline anisotropy constant K 1 as well as uniaxial anisotropy constant K u and gyromagnetic ratio γ are precisely determined for (111) magnetic garnet epitaxial films from measurements on FMR field orientation dependence. Strict FMR conditions are derived from total free energy expressions, where the differences between magnetization direction and applied field direction are taken into consideration. By applying magnetic field in (110) plane, FMR is measured to obtain the three best fitting parameters of K 1 , K u and γ. Present analysis is compared with Cronemeyer et als analysis. Influence of sample misalignment on measurement accuracy is also presented. Similarly, for (110) garnet films with orthorhombic magnetic anisotropy, measurements are carried out for two crystallographic planes of (001) and (110), and the four best fitting parameters of K 1 , K u , δ and γ are determined.

A Bloch Line Pair Generator Using the Flank Wall near the Stripe Domain Head for the Bloch Line Memory

A technique for injecting a vertical Bloch line (VBL) pair into a stripe domain head has been developed. This method utilizes horizontal Bloch line punch-through at the flank wall and successive domain chopping. The method is more practical than that of pushing the stripe domain head. In the new method, the domain is only controlled to lie beneath the conductor pattern for a VBL pair injection. Experimentally, a result of VBL pair injection is shown using 5 µm bubble garnet film and a reasonable margin is obtained in the pulsed bias field vs its width.

Electrical properties and charge imbalance for Ca,Ge‐substituted garnet films grown by liquid‐phase epitaxy from PbO‐BO fluxed melts

Ca,Ge‐substituted garnet films show p‐type conduction when grown from melts of Ca/Ge molar ratio, R5 parameter≡[CaO]/([CaO]+[GeO2]) ≳0.486. n‐type conduction is observed for films grown from R5‐parameter ?0.275 melts. Through experiments on Ge and/or Ca doping to (Y,Sm)3(Fe,Ga)5O12 garnet films, these dopants are concluded to play important roles in the resistivity, as well as the conduction type. It is inferred that Ca content in films exceeds Ge content for p‐type Ca,Ge‐substituted garnet films and that Ge content exceeds Ca content for n‐type films. These results are obtained from measuring resistivity and the sign of the Seebeck effect for (Y,Eu,Tm,Ca)3(Fe,Ge)5O12 garnet LPE films at room temperature. Both resistivity at melt saturation temperature and the conduction type depend on R5‐parameter values. Low‐coercivity films are reproducibly obtained from R5∼0.1 melts.

Dysprosium containing bubble garnet composition for ion‐implanted contiguous disk devices

A new bubble garnet composition containing dysprosium (DySmLuBiCa)3(FeGe)5O12 has been investigated for use in 4‐μm period ion‐implanted contiguous disk (CD) devices. The most significant property of the material is its low value of difference in magnetostriction constants, δλ(=λ100−λ111=+1.4×10−6). The low δλ is attained by substituting Dy ions into the dodecahedral sites. The Gilbert damping parameter α is moderate. The present Dy‐containing garnet showed several favorable characteristics with respect to bubble propagation in 4‐μm period He+ implanted CD devices. Those characteristics are (1) small minimum drive field, (2) suppression of bubble jumping to adjacent CD ‘‘good’’ tracks, even in 6‐μm loop period, (3) smooth followup of bubble positions to drive field directions, and so on. These characteristics in bubble propagation along CD tracks are interpreted by the in‐plane magnetization reversal at the pattern edge, which is related to δλ and stress relief. Smaller δλ decreases threefold symmetric be...

Easy Magnetization Axis of LPE Garnet Films Grown on Misoriented (111) GGG Substrates

It has been observed that the inclination angle of the easy magnetization axis is larger than that of the [111] axis in LPE bubble garnet films grown on GGG substrates slightly inclined from the (111) plane. This phenomenon was investigated in the light of Gyorgys 2-parameter model. The relationship between the inclination of the easy magnetization axis and that of the [111] axis was explained by employing -1.8 and -0.9 as the 2-parameter ratios, A / B , for (Y, Eu) 3 (Fe, Ga) 5 O 12 and (Er, Eu)3(Fe, Ga) 5 O 12 garnet films, respectively. The result suggests that the substrate surfaces of these garnets should be made up at least within ±0.25° and ±1.1° in reference to the (111) plane, depending on the magnitude of A / B for actual device works.

Three dimensional computer simulation of vertical Bloch line motion in a Bloch line memory

The motion of a pseudo-two dimensional wall is simulated by applying an ADI(Alternative Direction Implicit) method for the extended Slonczewski equation. The equation is solved implicitly in one of the two dimension of a magnetic domain wall alternatively in order to achieve a stable solution of the nonlinear differential equation. By this simulation, the real three dimensional(3D) motion of the vertical Bloch lines(VBLs) is obtained. The simulation results give information useful for Bloch line memory operation.

Effect of Pressure on Magnetic Properties of Heavy Rare Earth Binary Alloys

The magnetic transition temperatures T f , T c , T N and θ p , and effective number of Bohr magneton n eff have been measured as a function of pressure by means of a standard Hartshorn bridge under hydrostatic pressures up to 6 kbar. Here, T f , T c and T N are the temperatures of ferro-antiferromagnetic, ferro-paramagnetic and antiferro-paramagnetic transitions, respectively, and θ p , is the paramagnetic Curie temperature. The absolute values of the pressure derivative ∂θ p /∂ p have a minimum in the vicinity of the average value of de Genne factor of the alloys in the para-state, \bar G p =6.2, while those of ∂ T N /∂ p increase monotonically with increasing \bar G in the ordered state. Except Gd alloy system, the pressure coefficient of n eff , n eff -1 (∂ n eff /∂ p ), increases with increasing average number of 4 f electrons of the alloy, N , and changes the sign from negative to positive at about \bar N =10. The results obtained are discussed in terms of the molecular field approximation.

Ca-Ge Substituted Rare Earth Iron Garnet Primary Phase Region from PbO-B2O3 Fluxed Melts

The primary phase region of PbO-B2O3 flux grown bubble garnets with partial substitution by Ca2+ and Ge4+ up to 1.0 per formula unit, has been investigated. It was found that the following solute compositional relationship should be satisfied in order to obtain the garnet phase as a primary phase, when R1-parameter≡[Fe2O3]/Σ[RE2O3] is fixed at 20.0, [CaO]<0.7{[Fe2O3]+1/2[GeO2]-4}, where [CaO], [Fe2O3] and [GeO2] are the mole fractions of CaO, Fe2O3 and GeO2, respectively. In the vicinity of the outside of the garnet region, CaO precipitates as a primary phase.

Effects of magnetic and structural properties on magnetoresistance in amorphous TbFeCo

An extraordinary magnetoresistance effect, linearly dependent on the external magnetic field, is observed in amorphous TbFeCo films. The electrical resistance jumps by δρ at magnetization reversal. δρ depends on Tb concentration and it becomes nearly zero at about Tb 26 at. % concentration. To clarify the Tb concentration dependence of δρ, the magnetic properties and the heat treatment effect are examined. It is found that the magnetic anisotropy field (Hk ) is maximum at about Tb 26 at. % and the gradient of linear magnetoresistance, δρ/(ρ0Hc), is proportional to the −Hk+ const, where ρ0 is the electric resistance in zero field, Hc is the coercive force, and the constant is about 100 kOe. The structural relaxation, a coercive force change by the heat treatment up to 200 °C, is examined. It is found that as δρ/(ρ0Hc) in the as‐sputtered state decreases, the coercive force change by the heat treatment decreases. The coercive force change is minimum at about Tb 26 at. %, where δρ/(ρ0Hc) becomes zero. These ...

1‐μm bubble propagation errors in single‐layered ion‐implanted contiguous disk track

1‐μm bubble propagation errors in ion‐implanted contiguous disk devices are investigated in a single‐layered (YSmLuBiCa)3 (FeGe)5O12 (111) garnet film. In a good track with 4×4 μm unit cell, there are two main problems: (1) The minimum drive field was generally high, compared with 1/3 HKl, where HKl was named after Lin et al. (2) The bias margin was degraded at higher bias field for high drive field, when ion implantation was heavy. Problem (1) was found to be mainly due to the charged wall nongeneration in the cusps where bubble resided. Problem (2) was found to be due to ‖λ111‖ decrease caused by ion implantation.