Latest developments of the spin-valve transistor

The magnetic hysteresis associated with the magnetization reversal of the free layer in a spin valve is analysed. A model is proposed which assumes a single-domain behavior of the free layer, and a fixed magnetization of the pinned layer. The model is then developed in the framework of the Stoner¿Wohlfarth coherent rotation model, where geometrical solutions are obtained by the astroid method. According to the strength of the interlayer exchange coupling, the applied field direction and the anisotropy arrangement of the magnetic layers, a general classification of the hysteresis loops is proposed. Quantitative comparisons with experiments on spin valves (e.g. NiFe/Cu/NiFe/FeMn) are shown

Magnetization Process of High Anisotropy Copt Nanosized Dots

The magnetization reversal process of the CoPt dot was investigated in this paper. It was observed that the magnetization reversal of the dot was initiated by the rotation process of a nucleus with the volume of (17 nm)/sup 3/

Switching field and thermal stability of CoPt/Ru dot arrays with various thicknesses

The switching fields and thermal stability of CoPt/Ru dot arrays with various dot thickness delta (5-20 nm) were experimentally investigated as a function of the dot diameter, D, (130-300 nm). All dot arrays showed a single domain state, even after removal of an applied field equal to the remanence coercivity Hr. The angular dependence of Hr for the dot arrays indicated coherent rotation of the magnetization during nucleation. We estimated the values of the "intrinsic" remanence coercivity H0 obtained by subtracting the effect of thermal agitation on the magnetization and the stabilizing energy barrier to nucleation E0/(kBT). The variation in H0 as a function of delta and D was qualitatively in good agreement with that of the effective anisotropy field at the dot center Hk eff(r=0), calculated taking account of the demagnetizing field in the dots. The ratio of H 0 to Hk eff(r=0) for the dot arrays with delta=10 nm increased from 0.53 to 0.70 as D decreased from 300 to 140 nm, and no significant difference in the H0/Hk eff(r=0) ratio due to the difference in delta was observed. On the other hand, E0/(k BT) decreased as delta decreased. E0/(kBT) increased slightly as D decreased, but, was not so sensitive to D over the present D rang

Activation volumes in CoPtCr-SiO2 perpendicular recording media

CoPtCr-SiO2 perpendicular recording media with varying levels of SiO2 were examined by two different methods to determine the activation volume. The first is based on the sweep-rate dependence of the remanence coercivity using Sharrock's equation. The second is based on the measurement of the fluctuation field from time-dependence data, determined using a magneto-optical Kerr effect (MOKE) magnetometer. The values of V-act measured at the coercivity for both methods are almost the same, with the fluctuation field and activation volumes increasing with the SiO2 content. The difference between V-act and the grain volume measured directly from bright-field TEM images decreases as the SiO2 content increases due to the reduction of intergranular exchange coupling. The experimental results indicate that values of V-act obtained from single- and double-layered media are consistent. It was also found that the coercivity and normalized hysteresis loop slope at coercivity varied with SiO2 content, with the coercivity peaking at 8 at % SiO2 (nearly 26 vol% SiO2)

Thermal fluctuation of magnetization in nanocrystalline FePt thin films with high coercivity

科研費報告書収録論文(課題番号:11305027・基盤研究(A)(2)・H11～H12/研究代表者:中村, 慶久/柔軟なスピンクラスター配列からなる超高密度磁気記録メディアの研究

Thermal agitation of magnetization in CoCrPt perpendicular recording media

科研費報告書収録論文(課題番号:11305027・基盤研究(A)(2)・H11～H12/研究代表者:中村, 慶久/柔軟なスピンクラスター配列からなる超高密度磁気記録メディアの研究