Magnetization Curling Research Articles

Magnetization Model for Particle Magnetic Interaction

A new medium magnetization model that takes account of the magnetic interaction of particles has been developed. It is based on the curling magnetization reversal model, and incorporates Atherton's function for the mean field interaction. It is very easy to build the mean field function into the algorithm of our medium model. It is shown that the new medium model is very effective for Utting not only the M-H loops, but also the remanence characteristics of longitudinally oriented Ba-ferrite tape. It is expected that more precise simulation analyses will become possible through the use of this medium model.

Spherical center for nucleation by curling in a bulk ferromagnet

The process of nucleation of magnetization reversal in bulk materials by the magnetization curling mode is investigated by a numerical integration of an approximate differential equation. This computation shows that limiting the curling to a spherical shell does not lead to a saddle point, and that the energy which has to be overcome for reversing the magnetization by the curling mode is larger than that required for the previous, tilting mode. Therefore, the latter is left as the only practical nucleation center in bulk materials.

Magnetization curling in a fine cylindrical particle

Micromagnetic curling configurations in finite magnetically soft cylinders are studied by means of computer simulation. A simple model based on the variational principle is suggested. The model quantitatively describes the obtained resu;ts over a wide range of particle sizes.

粒子間相互作用を考慮した媒体磁化モデル

A new medium magnetization model that takes account of the magnetic interaction of particles has been developed. It is based on the curling magnetization reversal model, and incorporates Atherton’s function for the mean field interaction. It is very easy to build the mean field function into the algorithm of our medium model. It was shown that the new medium model is very effective for fitting not only the MH loops but also the remanence characteristics of longitudinally oriented Ba-ferrite tape. It is expected that more precise simulation analyses will become possible through the use of this medium model.

Development of a basic model for a 3-dimensional magnetic recording simulator

A basic model was developed for 3-dimensional analyses of the magnetic recording and reproducing processes. The curling magnetization reversal model used in our conventional 2-dimensional simulator was improved to calculate the 3-dimensional direction of a megnetization vector in a recoding medium. To consider the nonlinearity of a soft magnetic material, a recording head and an unser-layer of a Co-Cr/Ni-Fe double-layered medium were modeled by arctan function M-H loops. The magnetic field distribution was calculated by the magnetic charge distribution in both head and medium. The 3-dimensional distribution of the SPT head field was investigated when the head was combined with a Co-Cr/Ni-Fe double-layered medium.

Magnetization curling in an infinite cylinder with a uniaxial magnetocrystalline anisotropy

The magnetization curling mode for an infinite cylinder with a uniaxial magnetocrystalline anisotropy is considered. The angular dependence of the nucleation field HN and the coercive force Hc are estimated as a function of the radius, the magnetocrystalline anisotropy, and the inclination of the axis to the applied field. It is assumed that only curling and rotation in unison occur, and that the discontinuous jump by the curling mode brings the magnetization to the lower energy state given by Stoner–Wohlfarth. With this assumption, the rotational hysteresis loss Wr and integral Rh are evaluated both for an aligned and for a random assembly of infinite cylinders.

Magnetostatics of curling in a finite cylinder

The magnetostatic self energy is calculated for the magnetization curling mode in a finite cylinder, for the model proposed by Ishii and Sato [J. Appl. Phys. 65, 3146 (1989)]. It is shown that slight modifications of that model can eliminate all the cumbersome computations and allow all the integrations to be done analytically.

Analysis of Head to Medium Magnetic Interaction in Perpendicular Magnetic Recording by Finite Element Method Combined with Magnetization Model

A new simulation program has been developed for the analysis of perpendicular magnetic recording. This is the finite element method program which adopts a magnetization curling mode and a statistical method to calculate vectorial magnetizations in a medium. Using this simulation analysis, we could explain quantitatively the effects of the magnetic interaction between a single-pole head and a double-layer medium which were predicted from the experimental results. Furthermore, we were able to analyze a vectorial recording and reproducing mechanism. This new program is a very powerful tool which can more precisely simulate the magnetic recording process.

Magnetic behavior of a film with columnar structure

In order to see the magnetization process of a magnetic film with columnar structure, it is assumed that the magnetization in the ferromagnetic particles in the film reverses by magnetization curling in a finite cylinder, and that the field exerted on the particle is composed of the applied field and the field due to the poles of the other particles in the film. Then hysteresis loops are calculated. It is found that the hysteresis loops obtained in this work agree well with the experimental results on iron-alumite films, and that the calculated and observed minor loops are parallel to the H-axis. Moreover it is found that the coercive force of the film is independent of the separation between the particles, as seen in the experimental results.

Magnetization curling in a finite cylinder

In order to see the variation of the magnetization state in a finite cylinder, it is assumed that the magnetization changes its direction by the magnetization curling mode in which θ is given by θ=λ(z/L)2+ν, where θ is the deviation of the magnetization in the cylinder from the z axis which is the axis of the cylinder, L is half of the cylinder length, and λ and ν are the coefficients which specify the magnetization state. Finding λ and ν which minimize the total energy ε of the cylinder, we obtain the hysteresis loops and the coercive force. The coercive force obtained in this work agrees well with the experimental results for a cylinder 2.5 μm long and a diameter from about 50 to about 130 nm. It is also found that the configurations can be stable in which the magnetizations are not along the z axis, and the hysteresis loops are not rectangular, even though an applied field is along the z axis.

磁化モデルを組み込んだ有限要素法による単磁極ヘッド・二層媒体間磁気的相互作用の解析

A new simulation program has been developed for the analysis of perpendicular magnetic recording. This is the finite element method program which adopts a magnetization curling mode and a statistical method to calculate vectorial magnetizations in a medium. Using this simulation analysis, we could explain quantitatively the effects of the magnetic interaction between a single-pole head and a doublelayer medium which were predicted from the experimental results. Furthermore, we were able to analyze a vectorial recording and reproducing mechanism. This new program is a very powerful tool which can more precisely simulate the magnetic recording process.

Nucleation in a ferromagnetic sphere with surface anisotropy

The whole eigenvalue spectrum is studied for the nucleation field in a sphere with a uniaxial surface anisotropy. Detailed calculation is given for the magnetization buckling mode in such a sphere, which is the only reversal mode for rather small radii before the onset of the magnetization curling mode.

Magnetization curling in coated particles

Rigorous micromagnetic calculation is presented for the nucleation by the magnetization curling mode in an infinite circular cylinder, which has a uniaxial anisotropy (parallel to the cylinder axis) only in a cylindrical shell, on the surface. Numerical values used in a computed example are those of acicular γ-Fe2O3 particles, coated with CoFe2O4.

Surface anisotropy in micromagnetics

The conventional boundary conditions of micromagnetics are modified to include surface anisotropy of crystallographic nature, which is possible in epitaxy, or when surfactants are chemisorbed on the surface of ferromagnetic particles. As an illustration, the nucleation by the magnetization curling mode is calculated for a sphere with such a surface anisotropy.

Angular dependence of nucleation field in magnetic recording particles

Nucleation field of particles used for magnetic recording increases sharply for large angles between the applied field and the particle easy axis. This effect is shown to be consistent with the magnetization curling mechanism in these particles.

A split separator line merging model of the dayside magnetopause

A new magnetic field configuration in the magnetopause of an open magnetosphere is constructed by superposing a uniform field and the idealized Chapman‐Ferraro field. A straightforward interpretation of the results synthesizes previously unrelated models and observations: antiparallel and subsolar merging, uniform‐field‐plus‐dipole models, merging by the tearing mode instability, the magnetic curl configuration in laboratory terella experiments, flux transfer events, and accelerated boundary layer flows.

Validity of Finite Element Formulation and Solution of Three Dimensional Magnetostatic Problems in Electrical Devices with Applications to Transformers and Reactors

This paper shows that the three dimensional magnetostatic field formulation based on the magnetic vector potential curl curl equationi yields unique field solutions in the practical inhomogeneous, anisotropic case with a positive definite reluctivity tensor (laminated cores, etc.). It is also shown that this can be accomplished without the imposition of other constraints on the divergence of the vector potential, and still one obtains unique magnetic vector potential solutions. It will also be shown that in the finite element formulation, the stationary point of the energy functional is the minimum energy point.

Electron microscopy of CoCr sputtered films

The magnetization curling in the CoCr film is found by a high resolution Lorentz microscopy technique. Several grains assemble to form a column, and it is observed to behave as a magnetic cluster. The magnetization reversal process is performed by the rotational switching in the magnetostatically coupled individual cluster.

Rotational hysteresis and magnetization curling of elongated single-domain particles in Alnico permanent magnets

The rotational hysteresis energy has been measured as a function of the applied field for Alnico IX with a preferred orientation and a single crystal of Ticonal 900. The results have been compared with the theoretical values obtained from the Stoner-Wohlfarth and Shtrikman-Treves theories, The results are in good general agreement with the Shtrikman-Treves theory, and from measurements of the rotational hysteresis integrals and the angular dependence of the coercivities it has been concluded that changes in the magnetization occur principally by the curling mechanism.

On magnetic curl in front of the magnetosphere boundary

The structure of the magnetic field at the boundary of the artificial magnetosphere was studied with the southern component of the magnetic field in the plasma flow. It is shown that due to reconnection of the fields in the region of polar clefts the extended magnetic curl occurs that is disintegrated into smaller loops, magnetic islands. The comparison of the laboratory experimental results and the ISEE results of the magnetic measurements is given.