Rotation of magnetocrystalline easy axis in Ca2Fe2O5

摘要

An anomalous enhancement of the magnetic susceptibility of Ca2Fe2O5 taken in low magnetic fields applied perpendicular to the b axis has been reported to occur in the interval 60 K <= T <= 140 K, but with few experimental details and no explanation of the phenomenon. Reexamination of the magnetic susceptibility taken with H 10 Oe on a high-quality single crystal has corroborated the phenomenon in an interval 40 K <= T <= 140 K. A Weak ferromagnetic component in the a-c plane is induced by a Dzialoshinskii vector D-ij parallel to the b-axis. At temperatures T > 140 K, there is no irreversible displacement of domain walls in a field of H = 10 Oe. A step found in chi(m)(H parallel to b) at T-2 = 40 K signals the easy magnetization in the a-c plane is along the a-axis below T-2; spins along the a-axis are canted along the b-axis by the local anisotropies of the cooperatively rotated iron sites. Above T-1 = 140 K, the easy axis is the c-axis about which the Fe sites are rotated. In the interval T-2 <= T <= T-1, the magnetocrystalline anisotropy in the a-c plane becomes small, presumably as a result of a subtle structural change, which allows a field of only 10 Oe to rotate significantly the weak ferromagnetic component in the a-c plane toward the direction of an applied field of 10 Oe. In the higher magnetic fields used in most earlier measurements, displacements of domain walls induces a divergence of the field-cooled and zero-field-cooled curves at all temperatures T < T-N, which obscures the effect of a small magnetocrystalline anisotropy in the a-c plane in the interval T-1 <= T <= T-2. (c) 2005 Elsevier SAS. All rights reserved.