Particle-like magnetic behavior of rf-sputtered CoCr films

Abstract

This paper summarizes measurements on CoCr films that appear to indicate particle-like behavior of the magnetization reversal. The films studied were rf-diode sputtered onto glass substrates and had a magnetic moment of 400 emu/cm3 (at about 17 at. % Cr content). Particle-like structure of CoCr films has been reported by many authors because of the SEM fracture cross sections which show a columnar microstructure with long thin particles extending through the film thickness. Temperature variations of coercivity and anisotropy fields are found to track approximately indicating that the coercivity is primarily of crystalline origin but also the difference in the slopes of these curves is explained almost exactly by a particle model consistent with the SEM fracture cross sections. Preisach diagrams were constructed from the shear corrected hysteresis loops and found to be extremely narrow. Further, the Preisach data correctly predicts initial magnetization curves. The Preisach diagram results suggest a magnetization reversal model of particles that are magnetically noninteracting except for the sheet demagnetizing fields of the film. Much data exists to support the idea of phase segregation in the CoCr alloy system, again in support of the particle idea. Rotational hysteresis loss measurements were made which indicate magnetization reversal by way of a curling or buckling mechanism, again indicating a particle-like behavior. Coercivity as a function of field angle was measured yielding results consistent with curling or buckling as the primary reversal mechanism. Almost all available data is explained by a model of magnetically isolated particles that interact magnetically only through the film demagnetizing fields and individually reverse by curling or buckling.