A compensated/uncompensated independent mechanism of exchange anisotropy appearance using a model with loose coupling in the antiferromagnetic region

Abstract

SUMMARYSince its discovery, unidirectional anisotropy appearing in exchange coupled ferromagnetic (F)/antiferromagnetic (AF) layers has been used to pin ferromagnetic layers of various spin devices. However, a fundamental understanding is still lacking. The author has already demonstrated a mechanism based on simply assuming a loosely coupled layer in the AF region, without imposing any restrictions on the classical Heisenberg spins, with perfect compensated and uncompensated AF interfaces on the simple cubic (sc) lattice. The difference between compensated and uncompensated is only the F/AF coupling form (spin flop or collinear) interaction, and unidirectional anisotropy does not depend on the compensated or uncompensated case, but appears as a result of introducing loose coupling in the AF region. The unidirectional anisotropy energy does not come from the F/AF interfaces, but from the inner AF coupling defects. As reported in our previous papers, a large decrease in AF interaction from 1/10 to 1/1000 of the usual AF interaction was necessary in order to obtain unidirectional anisotropy in the systems. Correspondence between loose coupling and the defect mode, cell size dependency in the fcc system, and thickness dependency are topics for future investigation.