Huge magneto-optical effects in half-metallic double perovskites

Abstract

Using generalized-gradient-corrected full-potential density-functional calculations we have studied the magneto-optical properties of double perovskites A2BB8O6, A= Ca, Sr, and Ba; B= Fe; and B8 = Mo, W, and Re. Sr2FeWO6 has the maximum polar Kerr rotation of 3.87° and specific Faraday rotation of 4.5 3 10 5 deg cm ˛1 . All other compounds have Kerr rotation more than 1°, except Ca 2FeMoO6 which has maximum Kerr rotation of 0.5°. Our electronic structure studies show that all these compounds are half-metallic in the ferromagnetic configuration. The large Kerr rotation is found to be due to the combined effects of relatively large exchange splitting from Fe, large spin-orbit coupling due to 4 d or 5d elements, large offdiagonal conductivity, and half-metallicity. Materials with large magneto-optical (MO) effects have attracted a lot of attention in both basic and applied research. The motivation stems from desire to develop erasable MO memories and high density disks with MO readout. However, it is still a challenging problem to find a material with large MO rotation and also possessing a collection of necessary magnetic properties. The interaction of electromagnetic radiation with magnetized matter manifests itself as MO effects. The MO effect due to reflection is called MO Kerr effect (MOKE) and that due to transmission is called MO Faraday effect. Planepolarized light, when reflected from a metal surface or transmitted through a thin film that has nonzero magnetization will become elliptically polarized with ellipticity (e K in reflection mode and eF in transmission mode). The major axis is rotated by the angle u (uK in reflection mode and uF in transmission mode) relative to the polarization axis of the incident beam. The MOKE is of three major types, polar, longitudinal, and equatorial. The polar Kerr effect for which the direction of the macroscopic magnetization of the ferromagnetic material and the propagation direction of plane polarized incident beam are perpendicular to the plane of the surface, is the most interesting case and used in practical