Rotation of magnetocrystalline easy axis in Ca2Fe2O5

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 60K⩽T⩽140K, but with few experimental details and no explanation of the phenomenon. Reexamination of the magnetic susceptibility taken with H=10Oe on a high-quality single crystal has corroborated the phenomenon in an interval 40K⩽T⩽140K. A weak ferromagnetic component in the a-c plane is induced by a Dzialoshinskii vector Dij parallel to the b-axis. At temperatures T>140K, there is no irreversible displacement of domain walls in a field of H=10Oe. A step found in χm(H∥b) at T2=40K signals the easy magnetization in the a-c plane is along the a-axis below T2; spins along the a-axis are canted along the b-axis by the local anisotropies of the cooperatively rotated iron sites. Above T1=140K, the easy axis is the c-axis about which the Fe sites are rotated. In the interval T2⩽T⩽T1, 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