Kesami Saito

Large Interface Spin-Asymmetry and Magnetoresistance in Fully Epitaxial Co2MnSi/Ag/Co2MnSi Current-Perpendicular-to-Plane Magnetoresistive Devices

Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) characteristics were investigated in a Co2MnSi (CMS)/Ag/CMS fully epitaxial device and compared to those in a CMS/Cr/CMS device systematically. Reflection high-energy electron diffraction and transmission electron microscopy images showed the two samples had no remarkable differences and little interdiffusion. The large spin-asymmetry of electron scattering was found at the CMS/Ag inteface compared with that at the CMS/Cr interface. Finally, the largest magneto-resistance (MR) ratio of 28.8% was observed at room temperature in the CMS/Ag/CMS CPP-GMR device.

Magnetoresistance of Co-X/Cu multilayers

Abstract The effect of an additional element X (X = Cr, Mn, Fe, Ru, Pt or Ni) into Co layers on giant magnetoresistance (MR) of Co/Cu multilayers has been investigated. MR ratio for the Co-X/Cu multilayers is increased only in the case of Fe-addition. The concentration dependence of MR for Co x Fe 1- x /Cu multilayers has, therefore, been investigated in detail. Large MR ratio of 10–30% at room temperature for the Co x Fe 1- x /Cu multilayers can be obtained in a wide compositional range between x = 1.0 and 0.5.

Spin-wave resonance in ferromagnetic coupled Co/Cu multilayers

Abstract FMR experiments have been performed on [Co(50 A)/Cu(4 A)] 20 multilayers at room temperature by using an X-band ESR spectrometer and a series of spin-wave modes have been observed when an external field was perpendicular to the film plane. We have analyzed these spin-wave modes by spin-wave resonance theory of multilayers and obtained the interlayer exchange coupling constant.

Anomalous Pressure Dependence of the Giant Magnetoresistance for Co/Cu Magnetic Multilayers

The effect of pressure of up to 2.2 GPa on the giant magnetoresistance (GMR) has been investigated for sputtered [Co(10.8 A)/Cu( t Cu A)] 15 magnetic multilayers with various Cu-layer thicknesses, t Cu . It was found that the MR ratio, Δρ/ρ s , showing oscillatory behavior with t Cu , is strongly affected by the application of pressure at 4.2 K for the samples near the first peak ( t Cu =9.8 and 11.7 A): Δρ/ρ s for t Cu =9.8 decreases with increasing pressure, while Δρ/ρ s for t Cu =11.7 increases with increasing pressure. On the other hand, the pressure effect on Δρ/ρ s for the samples near the second peak ( t Cu =21.5 and 23.4 A) is much smaller than that near the first peak.

Magnetic characterization of thin Co50Fe50 films by magnetooptic Kerr effect

Magnetic properties of thin Co50Fe50 films on MgO(0 0 1) prepared with different annealing temperatures between room temperature and 300 °C are studied by vectorial magnetometry based on the magnetooptic Kerr effect. Independent from the annealing, the Co50Fe50 films reveal some similar magnetic properties, e.g. no quadratic magnetooptic Kerr effect and a magnetic reversal process which is completely in-plane with magnetic easy axes in Co50Fe50〈1 1 0〉 directions. If the alignment of the external magnetic field is close to the magnetic hard axes, incoherent rotation of magnetic moments between saturation and remanence occurs instead of coherent rotation as for the other directions. If the magnitude of the magnetization is polar plotted with respect to the azimuthal magnetization angle, sequential switching of magnetic moments from one magnetic easy axis to another can be proved by the course of the magnetization. Here, a two-domain switching process can be distinguished from a four-domain switching process generated by the incoherent rotation between saturation and remanence. Furthermore, both the uniaxial magnetic anisotropy constants and the domain wall pinning energies are determined from the magnetic switching fields using the Stoner–Wohlfarth model while the cubic magnetic anisotropy constants are obtained from fitting the magnetization curves. The domain wall pinning energies obtained from these analyses decrease with increasing annealing temperature due to fewer defects in the film. The cubic magnetic anisotropy also decreases slightly which can be attributed to relaxation of the crystal lattice for increasing annealing temperature due to a small change of spin–orbit coupling. Compared with the cubic magnetic anisotropy the uniaxial magnetic anisotropy is very small. This may be attributed to the reduction of strain in the film caused by a buffer stack Cr/Au/Cr between the Co50Fe50 film and MgO(0 0 1).

Phase Change of Zr-Al-N and Nb-Al-N Films Prepared by Magnetron Sputtering Method

In order to examine the critical content of AlN for phase change from B1 type to B4 type, Zr-Al-N and Nb-Al-N pseudobinary films were synthesized with an inductively combined rf-plasma assisted magnetron sputtering method. From phase identification of these films by XRD and Raman scattering methods, it is found that phase change from B1 structure to B4 one occurs in the range from 30mol%AlN to 35mol%AlN for Zr-Al-N pseudobinary films and from 62mol%AlN to 70mol%AlN for Nb-Al-N pseudobinary films. The critical AlN content for Zr-Al-N pseudobinary films shows excellent agreement with the value (33mol%AlN) predicted by band parameters. The critical content for Nb-Al-N pseudobinary films is larger than the predicted value (53mol%AlN). It is suggested that the disagreement is attributed to a highly defective structure in Nb-Al-N pseudobinary films.

Biquadratic Exchange Coupling in Epitaxial Co

Interlayer exchange coupling (IEC) behavior in epitaxial Co2MnSi (20 nm)/Cr/Fe (7 nm) trilayers has been investigated against Cr spacer thickness (tCr= 0.3-6.3 nm). High-quality trilayer samples have grown on a Cr (5 nm)/Au (30 nm)/Cr (15 nm) buffer layer on a MgO substrate by ultrahigh vacuum (UHV) compatible dc sputtering method. A simple numerical simulation model has been used to explain magnetization process, which shows good agreement with the experimental M-H curves. The values of bilinear and biquadratic coupling energy (J1 and J2) and the cubic anisotropy energy of Co2MnSi and Fe (KCMS and KFe) have been determined uniquely from the simulations. As a result, we have found a dominating contribution of biquadratic (90deg) coupling and absence of bilinear (180deg) coupling in all the samples with nonferromagnetic coupling. It has also been found that, the energetical competition between 90deg coupling energy and anisotropy energy largely affects the magnetization process due to different easy directions of bottom Co2MnSi (110) and Fe (100).

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Abstract We have studied the application of grazing-exit electron probe microanalysis (GE-EPMA) for surface and thin-film analysis. In this method, characteristic X-rays are measured at small take-off angles of less than 1°. Under grazing-exit conditions, the X-rays emitted from deep inside the sample are not detected because they are stopped by a slit mounted in front of the energy-dispersive X-ray detector. Hereby, it becomes possible to perform localized surface analysis with GE-EPMA. We applied this method to thin-film analysis of a small surface area. The exit-angle dependence of the characteristic X-ray intensities was measured for thin films of Cr and Ti. Thickness and density of thin films were determined by fitting the experimental plots with theoretically calculated curves. Differences were found in the densities of two Cr thin films deposited by magnetron sputtering and vacuum evaporation. The advantage of GE-EPMA is that non-destructive thin-film analysis of small surface areas can be incorporated in simple scanning electron microscope (SEM) analysis.

MnSi/Cr/Fe Trilayers

Abstract The influence of the addition of third elements into permalloy films on anisotropic magnetoresistance (AMR) has been investigated for a large number of third elements. AMR decreases rapidly for the addition of Sc, Ti, V, Cr, Ge, Zr, Nb, Mo, Ru, Ta and W. On the other hand, the decreases in AMR are relatively slow for the addition of Co, Cu, Pd, Ag, Pt and Au. We have found the tendency that the influence of the elements which are situated near Ni in the periodic table is smaller than that of the elements which are situated far from Ni.

Localized thin-film analysis by grazing-exit electron probe microanalysis

Abstract We have measured 63 Cu NMR spectra of [magnetic metal/Cu] superlattices synthesized by the ion beam sputtering method. The sample quality inferred from the NMR spectra has been found to depend strongly on the argon acceleration voltage, one of the important preparation conditions in sputtering.