Magnetic-field-induced spin flop transition and magnetoelectric effect in Ca2Fe2-xAlxO5

Magnetic-field-induced spin flop transition and magnetoelectric effect in noncentrosymmetric Ca2Fe2-xAlxO5 (0.5 <= x <= 1) single crystals have been investigated. Temperature dependence of magnetic susceptibility shows that the compounds have antiferromagnetic transition temperatures T-N above room temperature. The spin easy axis varies from the c axis to the a axis with increasing Al content x. When a magnetic field is applied along the spin easy axis, a spin flop transition takes place, accompanied by anomalies in the electric polarization and dielectric constant. The anomalies can be ascribed to a noncollinear spin arrangement in the domain walls between two magnetic phases and/or the spin direction dependent modulation of the metal-ligand hybridization. Such a polarization change with a spin flop transition in polar antiferromagnets may provide a route to realize large magnetoelectric coupling at high temperatures.