Spin fanning configurations in antiferromagnetic layers with a uniaxial anisotropy and torque transfer characteristics from top to bottom spins

Spin configurations along the thickness direction generated in antiferromagnetic (AF) layers with an in-plane uniaxial anisotropy have been calculated by numerical method. It is confirmed that when the bottom-surface anisotropy energy constant is less than 1/4 of 180 degrees-wall energy density, sigma(w), a sudden change or switch of the spin configuration occurs at a critical angle of the top spins when the AF-layer thickness, t, is greater than a critical value, t(c). This means that no hysteresis occurs with a rotation of the top spin for t<t(c). Spin configurations with a folded or periodic structure which Neel discussed have been revealed to be unstable without microscopic defects or irregularities which pin the spin angle at some depth from the top surface. It is found that when the bottom-surface anisotropy is lower than 1/4 sigma(w), the torque sustainable by the top-surface spins does not exceed 1/2 sigma(w). It is also found that the effect of top-spin rotation penetrates substantially down as deeply as a few times the 180 degrees-wall thickness. The effect of the AF-easy axis tilting out of the plane has also been studied. (C) 1999 American Institute of Physics. [S0021-8979(99)64208-6].