TABLE OF CONTENTS Many magnetic properties of thin films are sensitive to structure on levels of scale from the atomic to macrostructure. Advantage has been taken of this dependence on structure to create thin films with properties not observable in bulk solids. However, most magnetic properties do not exhibit the sensitivity to defect structure found for electrical properties and described in Chapter I. Some properties, such as coercivity in soft magnetic materials and the flux line pinning force in high temperature superconductors are affected by the defect structure. Many properties are sensitive to the morphology and dimensions of phases in a multiphase structure.
The properties desired from soft magnetic films used as inductive head core materials are large saturation flux density, low coercive field with small hysteresis losses, low magnetostriction (negative ? s), high initial permeability at high frequencies (i.e. no permeability decrease at high frequencies), small, but non zero, uniaxial anisotropy, low noise and a control over the domain structure in the various portions of the core.
The low coercivity alloy permalloy has a near zero value of the magnetostriction at the composition 81% Ni, 19% Fe and, hence, this composition is that preferred for thin film inductive recording heads, which almost always are under stress in the as-deposited condition. Most of the discussion to follow in this section relates to this material, except as noted. The magnitude of the detected signal increases with the saturation magnetization and permeability. The detection sensitivity of the inductive head...
