Magnetization reversal in a chain of oblate ellipsoids

Abstract

The model of the chain of two oblate ellipsoids is modified by calculating exactly the magnetostatic interaction energy between the ellipsoids and taking into account the effects of the number of the ellipsoids. The angular dependencies of the critical field H cri and the coercivity H c are determined analytically. The results show that the treatment of the magnetostatic interactions between the ellipsoids as dipole–dipole interactions is valid only for dimension ratio m( m= c/ a, a and c are the major and minor semi-axes of the oblate ellipsoid, respectively) approaching 1 or the separation ratio d( d= c/ D, D is the separation between two neighboring ellipsoids) approaching 0. The effective magnetic anisotropy constant K u, H cri and H c increase with increasing n and K (n is the number of the ellipsoids, K is the crystalline anisotropy constant). K u and H c decrease with decreasing m and d. For small m and large d, the effect of n on K u, H cri and H c becomes more pronounced. As K increases, the magnetization reversal mechanism of the chain tends more towards the parallel process. For constant K, the critical angle ψ 0 increases with m for large values of n, whereas the opposite effect occurs for small n.