Spin-1/2 Triangular Lattice with Orbital Degeneracy in a Metallic Oxide Ag2NiO2

A novel metallic and magnetic transition metal oxide Ag2NiO2 is studied by means of resistivity, magnetic susceptibility, specific heat and X-ray diffraction. The crystal structure is characterized by alternating stacking of a Ni3+O2 layer and a (Ag2)+ layer, the former realizing a spin-1/2 triangular lattice with eg orbital degeneracy and the latter providing itinerant electrons. It is found that the NiO2 layer exhibits orbital ordering at Ts = 260 K and antiferromagnetic spin ordering at TN = 56 K. Moreover, a moderately large mass enhancement is found for the itinerant electrons, suggesting a significant contribution from the nearly localized Ni 3d state to the Ag 5s state that forms a broad band.Comment: 9 pages, 5 figures, to be published in Rapid Communications, Phys. Rev.

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)

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

Discrete track media simulations for 600 Gb/in∧2 recording

Discrete track perpendicular recording media were simulated to determine the optimum conditions for achieving an areal density of 600 Gbits/in∧2. For a 90 nm track pitch the best performance was obtained form a medium with 60 nm land and 80 nm wide write pole. Comparisons with continuous media showed higher on- and off-track signal-to-noise ratio in some discrete track media, mainly due to the absence of erase band noise. Reducing the average grain size narrowed the differences between the two types of media, resulting in almost identical performance for an average grain size of 6 n

Simplified expression of shielded MR head response for double-layerperpendicular medium

科研費報告書収録論文(課題番号:09355012・基盤研究(A)(2)・H9～H11/研究代表者:中村, 慶久/垂直ハード磁気ディスク装置を用いる超大容量ストレージシステムの研究

Thermal relaxation in perpendicular double-layered media

科研費報告書収録論文(課題番号:09355012・基盤研究(A)(2)・H9～H11/研究代表者:中村, 慶久/垂直ハード磁気ディスク装置を用いる超大容量ストレージシステムの研究

Intergranular exchange pinning effects in perpendicular recordingmedia

科研費報告書収録論文(課題番号:09355012・基盤研究(A)(2)・H9～H11/研究代表者:中村, 慶久/垂直ハード磁気ディスク装置を用いる超大容量ストレージシステムの研究