Energy barriers for magnetization reversal of partially exchange-coupled particles

H. R. BERTORELLO; M. I. OLIVA; P. G. BERCOFF

JOURNAL OF ALLOYS AND COMPOUNDS

Año: 2004 vol. 369 p. 62 - 65

0925-8388

We study the magnetization reversal of a two-particle system with partial exchange coupling. We assume that the particles are discs and that the exchange coupling occurs through one of their plane faces extending up to 5lw into each particle (lw = (A/K)1/2). The easy axis of particle 1 coincides with the direction of the applied magnetic field H and the one corresponding to particle 2 is such that both easy axis are parallel to the contact face. We assume that the spins reorientation across the contact plane is similar to that of a Bloch wall. We write the free energy E of the system in terms of the fraction â of volume affected by exchange coupling, taking into account the anisotropy and exchange energies due to the spin reorientation and to the fraction (1-â) of non-interacting particles’ volume. For a given volume V the fraction â can be varied by sliding one particle with respect to the other, changing only the contact area. We calculate the ratio E/KV as function of H considering the easy axis of particle 2 at different angles with respect to the easy axis of particle 1. We determine magnetic moments switching paths together with the energy barrier DE for switching. We find a general expression of the form DE/KV = (1 − H/H0)z, with H0 = H0(â, ù) and z = z0 + á(ù)â, being z0 and H0(0, ù) equal to the values for non-interacting particles. We discuss the switching behavior as a function of ù and H.