Static and Dynamic Behavior of Thin Permalloy Films

Abstract

Thin magnetic films (∼1000 A) evaporated onto a heated glass substrate in the presence of a dc magnetic field develop a uniaxial magnetic anisotropy energy of the form Ek=Ksin2φ, with φ measured from the deposition field. Such films promise to outperform ferrite cores in digital-computer memory-systems by several orders of magnitude. A detailed static and dynamic theory based on the above anisotropy energy and the Landau-Lifshitz dynamical equation is presented. The static theory contains the unique feature of the coercive force parallel to the easy axis being dependent on a field in the plane of the film and perpendicular to the easy axis. Experimental verification of the theory is given. The dynamic theory considers both steady-state and pulse response. The steady-state solution is well known; the pulse solution must take very careful account of all the important torques acting in a switching experiment, and numerical results are obtained by the use of a digital computer. Experimentally, steady-state resonance is measured from 100 to 10 000 Mc and pulse switching down to 3 mμsec. Both types of experiment are in good agreement with each other and with the theory.