Huei Li Huang

Thermal relaxation of interacting fine magnetic particles – field-cooled and zero-field-cooled magnetization variation

Dipole interaction makes average energy barrier of magnetic fine particles for thermal relaxation reduced while the corresponding blocking temperature distribution is a function of both dipolar interaction strength and particle size distribution of the system. Flatness and fast drop-off of the λ-shape behavior of the field-cooled and zero-field-cooled magnetization varies with both dipolar intereaction strength and field level applied.

Reversible transverse susceptibility of particulate recording media

The response of a system to an infinitesimal perturbation becomes singular if the system changes its degree of metastability, i.e., if it has an inflection point. This theory is used to calculate the reversible transverse susceptibility χt of a single domain particle executing a major hysteresis loop under the influence of a field H(t) applied at an angle β to the easy axis. Thermal relaxation is taken into account and the response of the nonequilibrium system to the infinitesimal field h(t)=h sin ωt, h⊥H, is found. The resultant χt is studied as a function of β, temperature, and of the frequency Ω of the biasing field H.

Generalized equations for domain wall dynamics

Generalized domain wall dynamic equations have been derived. The influence of the external magnetic field normal to the anisotropy axis on the critical parameters of the domain wall motion has been studied and illustrated.

Calculation of exact head and image fields of recording heads by conformal mapping

An exact conformal mapping calculation is carried out, which maps the entire upper edge of an idealized ring head and a symmetric thin-film head in the complex z plane to the real axis of the complex t plane, and uses the slotted-plane approximation to obtain the inverse mapping function t(z). The latter is used to calculate not only the head fields of a given geometry, but also the kernal function to evaluate the total demagnetization field of the interaction head-media system including the media self-demagnetization and the image field induced on the head poles. The total demagnetization field contours for a single-bit arctangent transition and a dibit biquadratic transition corresponding to various head configurations have been obtained and their physical meaning elaborated on. >

Comparison of ring head and SPT head write fields

The coefficients of Fan ring head and single-pole-type (SPT) head of various gap widths/pole thicknesses were evaluated and the head field distribution for various configurations and flying heights were calculated. For easy visualization in comparison with Karlquist field the head fields are expressed in reduced units as H\min{xy}\max{F} = H\min{xy}\max{K}+ H\min{xy}\max{C} where F, K, and C stands for Fan, Karlquist, and correction terms, respectively. The results show the following. 1) The ring head coefficients are independent of gap width while the SPT head coefficients vary with the ratios of pole thickness to flying heights. The latter coefficients approach that of the ring head in the limit if it is properly redefined, indicating similarity and dissimilarity between the two head fields. 2) In the gap region the write field of a ring head F\min{Rx}\max{F} bends downward in comparison with Karlquist field, reaching approximately 0.82 at very low flying heights. 3) The x-component ring head field H\min{Rx}\max{F} differs considerably from the y-component SPT head field H\min{py}\max{F} when measured along the direction of media motion. The two fields behave similarly to each other only if each is measured along the direction of its own image plane.

Thermal relaxation, textural and sweep rate effects on reversible transverse susceptibility of magnetic particles

We investigated the effect of thermal relaxation on reversible transverse susceptibility (RTS), χ, of single domain Stoner–Wohlfarth particles. We studied such an effect as a function of the orientation β of the easy axis with respect to the drive field (the z axis) within a non‐interacting bi‐state model. At β=00 one prominent cusp occurs for both χt1 and χt2 along the direction perpendicular to the drive field at H≂HC<HN (nucleation field) at high values KV/kBT (the ratio of the anisotropy energy versus thermal energy). The height of the cusp varies with β and reduces with decreasing values of KV/kBT. Correspondingly, the switching field distribution (SFD) becomes broadened with decreasing values of KV/kBT. The RTS may exhibit one, two, or three prominent cusps at high values of KV/kBT depending upon the textural distribution of the easy axes. For cos2 θ distribution of the easy axis about the x axis, y axis, and z axis there exists two, three, and one cusps, respectively. For random distribution of the...

Equations of Domain Wall Motion In Ferromagnetic -- Medium With Q /spl ges/ 1

The domain wall dynamics in an infinite ferromagnetic medium with material quality factor Q>or=1 in the presence of a magnetic field normal to the anisotropy axis and at the same time parallel or normal to the wall plane are studied. Generalized equations reduce exactly to those of Slonczewski when the quality factor Q is much greater than unity. >

Domain wall structure dependence on the arbitrarily oriented external field

Abstract Simultaneous variation of the magnetization angles (ϑ, ϕ) across the DW proper and the DW energy variation versus the transverse magnetic field h t has been studied for the pinned domain wall. When the ψ H angle of the magnetic field is π/2 the DW will undergo the phase transition to a homogeneous state at a relatively small field of h t = 0.225.

On switching field dependence of the thermally excited single domain particles

Analysis of the characteristic dependency of the switching field distribution of a system of noninteracting single domain particles was conducted based on the bi-state, nonequilibrium probabilistic approach. The analysis was carried out as a function of applied field orientations, transition energy barrier variation, and in combination with a given distribution of the particle size and anisotropy constant, under the influence of thermal relaxation. The concept of the blocking temperature that the energy barrier being approximately equal to /spl sim/25 k/sub B/T was shown to be invalid unless the period of the field sweep is /spl sim/1 h.

Pinned domain‐wall structure in magnetic field

The pinned domain‐wall (DW) structure is investigated using a perturbational approach in terms of the inverse quality factor 1/Q and the ratio of H∥/Hk (H∥ being the component magnetic field parallel to the anisotropy axis, Hk being the anisotropy field). The parallel component field gives rise to asymmetric boundary conditions which asymmetrize the DW structure. Dependence of the DW energy, static DW structure, and width on the orientation and the strength of the magnetic field has been evaluated and the corresponding Kondorsky function obtained.