Effect of Crystallite Size on Coercive Force of Thin Ferromagnetic Films

Abstract

This paper describes the effect crystallite size has on the coercive force Hc of thin ferromagnetic films. Crystallite size was determined by the use of x-ray diffraction using a small angle between the x-ray beam and film samples. Films in this study ranged in thickness from 150 to 1750 Å with crystallite size from 50 to 950 Å and Hc values of 2.1 to 8.4 Oe. It was found that Hc is dependent on the crystallite size for films that have domain wall widths larger than the crystallite size. The data exhibits a decreasing Hc as the crystallite size increases for films with Néel or crosstie domain walls. For films with Bloch walls and crystallite size greater than the domain wall width, there is no apparent dependence on crystallite size of Hc. To a first approximation, the results of this study are shown to agree with the anisotropy constant variation term from Middelhoek's semiquantitative theory for coercive force of thin magnetic films. For films with domain wall widths larger than the crystallite size, this term contributes to the over-all coercive force.