Structural and doping effects in the half-metallic double perovskiteA2CrWO6(

Abstract

The structural, transport, magnetic and optical properties of the double perovskite A2CrWO6 with A = Sr, Ba, Ca have been studied. By varying the alkaline earth ion on the A site, the influence of steric effects on the Curie temperature TC and the saturation magnetization has been determined. A maximum TC = 458 K was found for Sr2CrWO6 having an almost undistorted perovskite structure with a tolerance factor f ≃ 1. For Ca2CrWO6 and Ba2CrWO6 structural changes result in a strong reduction of TC. Our study strongly suggests that for the double perovskites in general an optimum TC is achieved only for f ≃ 1, that is, for an undistorted perovskite structure. Electron doping in Sr2CrWO6 by a partial substitution of Sr 2+ by La 3+ was found to reduce both TC and the saturation magnetization Ms. The reduction of Ms could be attributed both to band structure effects and the Cr/W antisites induced by doping. Band structure calculations for Sr2CrWO6 predict an energy gap in the spin-up band, but a finite density of states for the spin-down band. The predictions of the band structure calculation are consistent with our optical measurements. Our experimental results support the presence of a kinetic energy driven mechanism in A2CrWO6, where ferromagnetism is stabilized by a hybridization of states of the nonmagnetic W-site positioned in between the high spin Cr-sites.

Electronic structure of the ferromagnetic double-perovskites Sr2CrReO6, Sr2CrWO6, and Ba2FeReO6

“…This leads to a complete spin polarization at the Fermi level, which immediately suggests their application as a source of spin polarized charge carriers in spintronic devices. Ferromagnetism with a T c up to 458 K has been observed not only in Sr 2 FeMoO 6 but also in ceramic and thin films of Sr 2 CrWO 6 [2]. The double perovskite with the highest T c known so far is Sr 2 CrReO 6 with T c =635 K [3,4].…”

Evidence of kinetic-energy-driven antiferromagnetism in double perovskites: A first-principles study of La-dopedSr2FeMoO6

“…The choice of B and B ions, provide the tunability of B-O-B interaction, giving rise to a variety of magnetic properties like ferromagnetism, antiferromagnetism, ferrimagnetism and electronic properties like metallic, half-metallic and insulating 6,7 . The presence of two transition metal ions instead of one as in perovskite material is expected to give rise to far more tunability and richness of properties compared to simple perovskites.…”

High-temperature multiferroicity and strong magnetocrystalline anisotropy in3d-5ddouble perovskites

“…However, recent work on new 3d − 5d double perovskites 13,14 showed this to be a misconception, and identified a ferrimagnetic insulator, Sr 2 CrOsO 6 , with magnetic ordering temperature well above room temperature. First-principles calculations have been shown to accurately reproduce the measured magnetic ordering temperatures 15,16 , in the Sr 2 CrMO 6 series (M = W, Re, Os) 17 , and have been invaluable in explaining the origin of the robust ferrimagnetic ordering [18][19][20][21] .…”