Effective single-domain diameter of a fine non ellipsoidal particle

Summary form only given. It is well known that the notion of a single-domain ferromagnetic particle can be introduced, strictly speaking, only for a particle of ideal ellipsoidal shape. On the other hand, for a non ideal particle (cube, parallelepiped, cylinder, etc.) according to Brown´s suggestion one can define an effective single-domain diameter as a characteristic length at which the reduced energy of a stable quasi uniform, i.e. flower, state of the particle coincides with that of the lowest non uniform (´multi-domain´) state. Of course, this quantity may depend on the actual particle´s shape. Therefore it is interesting to investigate how much the quantity defined differs from the single-domain size of an ellipsoidal particle with the same material parameters and aspect ratio. In this paper numerical simulations are made for soft type parallelepipeds and cylinders with different aspect ratios, m = L/sub z//D = 1, 2, 3, where L/sub z/ is the length of the particle and D (or L/sub x/) is the transverse particle´s diameter. A direct integration of the Landau-Lifshitz-Gilbert equation, as well as the LaBonte method were used in the simulations according to the usual scheme. To compare the data with our earlier results on spheroidal particles the same material parameters were adopted, namely, saturation magnetization M/sub s/ = 550 emu/cm/sup 3/, exchange constant C = 2A = 2/spl times/10/sup -6/ erg/cm, uniaxial anisotropy constant K/sub 1/ = 10/sup 4/ erg/cm/sup 3/. To insure reasonable accuracy the size of the numerical cell, l/sub 0/ /spl ap/ 5 - 7 nm, was chosen to be sufficiently small with respect to the exchange length, R/sub 0/ = C/sup 1/2//M/sub s/ /spl ap/ 26 nm.