M. Iizuka

A three-dimensional measuring method for magnetic stray fields

Reconstruction of three-dimensional microstray magnetic fields from a set of deflection data of electron probes deflected by the Lorentz force when passing through the object magnetic field is described. A novel reconstruction technique based on the ART (algebraic reconstruction technique) iterative method for electron beam tomography is proposed. In computer simulation, the algorithm was tested with a model example of a one-turn coil, and the achievable resolution is discussed. The algorithm was also checked experimentally with a one-turn oil and a commercial magnetic head. From these results, it is shown that the proposed method is applicable to high-intensity magnetic field reconstruction problems in electron beam tomography. >

Analysis and design of a metal-in-gap head for rigid disk files

Design improvements of the metal-in-gap head for rigid disk files, using a finite-element method that takes into account magnetic saturation, are discussed. The saturation flux density and the thickness of the alloy film and the throat height of the head are discussed analytically in order to obtain a more intensive and sharper field. The proposed analytical design is confirmed by measurements using an improved scanning electron microscope. The calculated and measured field results are in close agreement. >

Zig-zag transition region of bit written by various heads

The zig-zag transition region of magnetization reversals written by ferrite, MIG (metal-in-gap), and thin-film heads (TFHs) on a thin-film disk is surveyed from the viewpoint of the writing head field. Zig-zag transition lengths are evaluated through colloid-SEM (scanning electron microscopy) observations. Writing head fields are analyzed using the finite-element method, with magnetic saturation taken into account. It is found that zig-zag transition lengths are in inverse proportion to the head field gradient until they reach a minimum length depending on medium characteristics. The effect of the field gradient on the transition length agrees with previous theoretical analysis. It is clarified that lack of saturation of the trailing core in the MIG head and a high incident angle of flux from the interior of the core to the surface in the TFH are responsible for the high field gradient. This furnishes a head design guideline for high-density recording on thin-film disk by means of writing a shorter zig-zag transition length. >

Further discussion on magnetic vector potential finite-element formulation for three-dimensional magnetostatic field analysis

A linear soft-iron and current model called the IEE Japan model using a novel vector potential finite-element formulation is examined. Calculated and measured results are in close agreement. For comparison, the same model was calculated by the conventional variational formulation. The divergence of magnetic vector potential equals zero at the boundary of different materials and the values themselves are small enough at the Gaussian quadratural points, which means that uniqueness of the solution is guaranteed. The gauge condition is determined by the formulation, not by the boundary conditions. The new formulation requires less computing time and memory than the conventional variational formulation. >

New formulation of finite-element method with gauge condition for three-dimensional magnetic field analysis

A novel magnetic vector potential formulation for three-dimensional problems is described. In order to establish the boundary conditions of different materials, it is necessary to impose some kind of gauge for three-dimensional magnetic field analysis. The partial differential equation including the gauge is discretized using the Galerkin method, which in turn yields a new formulation. The three components of A are formulated separately. By separating the components, memory size and calculation time are reduced greatly. The calculated results show that the formulation is valid. >

Fast and stable non-linear converging method

In this paper, a non-linear converging method in the finite element analysis for magnetic field problems is proposed. Two types of materials with different saturation characteristics are considered. One has a gradual saturation characteristic called gradual saturaion, the other has a quick saturaion characteristic called quick saturation. A simple model, in which the value of magnetic flux density B for the applied magnetic field H can be evaluated analytically, is used for the numerical calculation. It is known that for materials with gradual saturation, the Newton-Raphson method is efficient for non-linear converging. For the materials with quick saturation there are some examples in which it does not work well. Conditions for the Newton-Raphson method to be applicable are studied both theoretically and numerically. A new, fast and stable iterative method with some sort of relaxation is proposed. Using some numerical examples, it is shown that the fast and stable convergence in the numerical analysis for material with gradual saturation and that with quick saturation is obtained.

Influence of Head Fields and Media Properties on Transitions of Magnetization Reversals on Thin Film Disk

This paper describes a relationship between transition lengths and head fields for media of various coercivities. Signals with various transition lengths were written using a single-sided and a double-sided MIG head on three different thin film media, of coercivity 874, 1121 and 1270 Oe. The transition lengths were observed by the colloid SEM method. The head fields of the MIG heads were analyzed by the finite element method (FEM) with magnetic saturation taken into account. The following phenomena were discovered: (1) the secondary fields stray from the saturated ferrite region near the interface between the metal film and ferrite core of the MIG heads; (2) the transition lengths are elongated due to the influence of the secondary field when the strength of the secondary field is greater than half of the medium coercivity. On the other hand, if the medium coercivity is twice as great as the secondary field strength, then the transition length is closely related to the field gradient of the primary field in the recording zone.

Design of a metal-in-gap head for higher coercivity media

The authors describe the design of a metal-in-gap head for high coercivity (>2 kOe) media by using the finite-element method. The secondary field at the metal-ferrite interface as well as the recording field strength and the recording field gradient is taken into consideration for the various structures of metal-in-gap heads. It is shown that by setting the film thickness of the trailing side larger than that of the leading side the secondary field can be reduced. Measured results have shown the validity of the design concept and that 33 dB of overwrite is obtained on the high coercivity (H/sub c/=2150 Oe) medium by the designed head. >

MFM Images Obtained by Electrodeposited Magnetic Tips

MFM images of a magnetic head and a recording medium, obtained using electrodeposited FeNi, Co and FeCo tips, show quite different features. These differences are explained by the magnetic properties, saturation magnetization and coercive force of the magnetic thin films electrodeposited on the tungsten wires to form the tips. We attempted to observe the magnetic structure of the tip by using magnetostatic bacteria that swim along the lines of the magnetic field originating from the poles on the tip.

Development of MFM-SEM System for Observation of Magnetic Domains

The magnetic force microscope (MFM) has the potential of enabling observations of fine magnetic domain structures, but remaining problems must be resolved before practical application is possible. As a result of theoretical analysis, the most suitable values of the probe-sample distance h and probe radius R were found to be h = 600 Å and R = 100 Å. Using these values, an MFM cantilever of length 130 ¿m, width 10 ¿m and thickness 1 ¿m was designed. A scanning tunneling microscope (STM) was used to detect the cantilever displacement resulting from the magnetic force. A new domain configuration was observed by scanning electron microscopy (SEM) by bringing a sharp Fe wire tip close to a sample and observing the influence of the leakage field of the tip.