K. Shinagawa

Thin permalloy film - bulk ferrite composite head for perpendicular magnetic recording

A composite head of thin permalloy film and bulk ferrite has been developed for perpendicular magnetic recording, which is designed to operate from only one side of the recording medium. This head has been fabricated mostly by means of vacuum evaporation, sputtering and photo-lithography. The writing and reading efficiencies have been confirmed to be as good as for a ferrite ring type head, by using Co-Cr films with a soft magnetic layer of amorphous Co-Mo-Zr. Higher bit density is obtained by a thinner pole tip head, though there is a sacrifice of output at lower bit densities. The highest bit density, D 50 , of 57 kBPI has been attained with a pole tip thickness of 0.3 μm. Computer analysis shows that a decrease of output at lower bit densities with decreasing pole tip thickness is attributed to the magnetic saturation of the pole tip. It is thus concluded that in order to improve head performance, it is necessary to increase the saturation induction of the pole tip material.

New Simulation Model for Perpendicular Recording Co–Cr Medium

Numerical analysis of a Co-Cr medium-ring type head system for perpendicular recording are performed using a two dimensional model with a finite element method. A new magnetization model of the Co-Cr medium is proposed, a columnar structure being taken into consideration. The medium is divided into elements for the calculation and an additional field, Had∝( Mupper+ Mlower) is assumed to be applied from upper and lower elements within a column, where M is the magnetization of the element. The results of the simulation show that the interaction between elements plays an important role in the magnetization process of the Co-Cr medium.

Development of 3-D read/write simulation system for higher areal recording density

Recently, higher areal recording density of hard disk drive (HDD) is achieved by increasing not only linear density (bits per inch) but also track density (tracks per inch). Then, three-dimensional (3-D) read/write (R/W) simulation is necessary in order to design a high-density recording system by utilizing magnetic field analysis. In this paper, a 3-D R/W simulation system using the edge-based finite-element method (FEM) is developed by introducing the 3-D medium hysteresis model based on the ensemble of the Stoner-Wohlfarth (SW) particles. As it is not easy to apply the Newton-Raphson method for the nonlinear analysis of SW model, an underrelaxation iteration method is used. The effectiveness of the 3-D R/W simulation system is illustrated by applying to the magnetic field analysis of a SPT (single-pole-type) head/DL (double-layer) medium perpendicular recording system.

Charge transfer-originated large Faraday rotation in Rh4+-substituted magnetic garnets

A large Faraday rotation is reported for Rh4+-substituted magnetic garnets in the near-infrared wavelength region. The Faraday rotation at 0.9 μm is about seven times larger than that in yttrium iron garnet by substituting Rh4+ ions of only 0.13 per formula unit at room temperature. From the electronic state calculations of a (Rh4+O62−)8− octahedral cluster performed by using an unrestricted self-consistent field–scattering wave–X α method, the origin of the Faraday rotation is attributable to the charge transfer transitions of an electron from O 2p to Rh 4d orbitals, or t1un(2p)→t2g*(4d) and t2un(2p)→t2g*(4d) transitions. Based on this assignment, the Faraday rotation spectrum is calculated by taking into account the spin–orbit interaction and the molecular field from iron magnetizations in the magnetic garnet.

Critical behavior of transverse and longitudinal ac susceptibilities in a random anisotropy magnet a-Dy16Fe84

Abstract We have investigated critical lines in the H-T plane in a random anisotropy magnet (RAM) a-Dy 16 Fe 84 with a small effective ratio of the anisotropy ( D ) to the exchange constant ( J ) by means of ac susceptibility (χ) in static fields H parallel and perpendicular to the ac field. We found that the transverse χ exhibits an anomaly along the irreversible line H ( T f ) determined by previous magnetization measurements, while the longitudinal χ does so along a characteristic line H ( T i ) in a lower temperature region. Above H ( T f ) we also found an extra characteristic line H ( T c ). The lines were almost independent of the measured frequency. Both the present results and previous magnetization results suggest that an equilibrium phase transition occurs, and the critical lines analogous to those in Heisenberg spin glasses are present in a weak RAM.

180° wall movement in a magnetic thin‐film closure domain structure in a high‐frequency field

The dynamic behavior of a 180° wall was observed in a Co‐based amorphous alloy film using a Kerr microscope. As a function of an anisotropy direction the amplitude of the 180° wall movement was measured with the drive field applied transverse to the 180° wall of the closure domain structure. The anisotropy direction was varied by magnetic heat treatment. It was found that the 180° wall moved independently of the anisotropy direction, that is, the 180° wall movement is related only to the applied high‐frequency field. To clarify the cause of the 180° wall movement, the magnetic energy of the domain structure and the eddy current loss caused by the high‐frequency field were calculated. However, the movement could not be understood completely in terms of energy balance since the magnetostatic energy increases faster than the decrease of the eddy current loss, when the 180° wall moves.

A lack of coherent reversal of the subnetwork magnetizations at the compensation temperature in an amorphous ferrimagnet with random anisotropy

Abstract Negative magnetization ( M ) below about the compensation temperature ( T comp ) was observed in amorphous Dy 0.21 Fe 0.79 at a small field ( H ). To investigate the anomalous phenomenon, Hall resistivity (ϱ H ) and magneto-optic Kerr rotation (θ K ), which give a complementary information to M , were measured. No changes of the signs in ϱ H and θ K at T comp were observed corresponding to M when H is small. These results suggest a lack of coherent reversal of the subnetwork magnetizations at T comp in Dy 0.21 Fe 0.79 . The unusual phenomenon was discussed in terms of random anisotropy.

Analysis of domain structure by calculating magnetostatic energy for magnetic thin film

A method of calculating magnetostatic energy is studied by a two‐dimensional approximation. This is required in order to analyze the domain structure of a magnetic thin film. The energy Es is calculated as the product of demagnetization field Hd and magnetization M. Since Hd varies widely within a domain, Es must be calculated in a number of subdivided regions in which Hd is assumed to be uniform, and their summation is calculated. Good precision can be achieved by subdividing a domain along possible charged surfaces. The closure domain structure of a rectangular film whose triangular domain has an extra wall is thus analyzed. Although the total energy of the film is increased by the addition of an extra wall, the local energy of the triangular domain has a negative minimum value when the magnetization direction is inclined. The calculated magnetization direction corresponding to the minimum energy agrees with the observation by scanning electron microscopy. Thus, it becomes clear that this domain structu...

Read/write simulation of keepered medium/spl middot/thin film head system

Two-dimensional read/write simulation based on the Maxwell equations is performed on a keepered medium (KM) with a thin soft magnetic layer (keeper layer) over a recording layer and a thin film head system by a finite element method. The keeper layer with the relative permeability /spl mu/ of 100 and the thickness t of 15 nm reduces the demagnetizing field in the recording layer (Mr=560 kA/m, t=36 nm, Hc=167 kA/m) by 1/2, and as a result, the recorded magnetization increases by 1/4. The optimum /spl mu/ of the keeper layer lies between 80 and 140. The spacing loss for an unkeepered medium (UKM) is consistent with the theory, but the one for the KM decreases considerably for low magnetic spacings. The magnetic spacing of 30 nm for the KM is equivalent to that of 13 nm for the UKM.

Temperature Dependence of Faraday Rotation in Co 2+-Substituted Hexaferrites

The temperature dependence of the Faraday rotation in the near-infrared wavelength region is calculated in comparison with that observed in Co 2+ -containing hexaferrites by using the molecular field approximation. The calculation results show that the Faraday rotation decreases in the whole wavelength region and shifts to a lower energy with an increase in temperature, which is in agreement with the experimental results.