The response of an iron whisker to longitudinal applied fields is studied theoretically and experimentally. Longrange magnetostatic interactions are found to play the dominant role in the magnetization process. The micromagnetic equations are solved for the transverse magnetization of the long domains in the Landau configuration and we find (i) the volume charge is always negligible for any crystalline anisotropy, (ii) the 180•‹ wall charge depends on anisotropy and for iron never exceeds 2.3 percent of the total magnetic charge, (iii) most of the charge is on the surface and a close analogy exists between the whisker and a bar of infinite intrinsic magnetic susceptibility. This analogy is used to find the longitudinal magnetization of the whisker in an arbitrary applied magnetic field. Maxwell's equations are solved self-consistently over the length of the bar and the procedure is extended to finite intrinsic susceptibility. In addition, approximate calculations of the demagnetizing energy are used to compute the susceptibility. In a series of experiments a whisker is used as a transformer core with various d.c. bias fields. The magnetization in a cross-section at different positions along the whisker is determined for several length to width ratios. The results are in excellent agreement with theory. To our knowledge, this is the first time the micromagnetic equations have been solved for the magnetization in a 3-dimensional multidomain specimen in an applied field Ho. As a result of these studies, we have been able to construct a picture of the spatial variation of magnetization in an iron whisker during the magnetization process.

http://summit.sfu.ca/system/files/iritems1/3380/b13787652.pdf

Magnetostatics and the micromagnetics of iron whiskers

The earlier successful techniques for numerical solution of magnetic field problems required defining a field quantity and magnetic permeability over the problem grid model. Later improved but limited techniques were introduced whereby it was necessary to define only a field quantity, usually a potentia function, over the grid because the magnetic material characteristics were incorporated directly into the equations. The work presented in this paper represents a culmination of these latter efforts in that technique is presented whereby the general three-dimensional magnetic field boundary value problem with current regions can be solved numerically.

R. Harden

Papers

Nonlinear magnetic field solutions based on a vector magnetic potential