Double perovskites with ferromagnetism above room temperature

Abstract

We review the structural, magnetic and transport properties of double perovskites(A2BB′O6) withferromagnetism above room temperature. Ferromagnetism in these compounds is explained by an indirectB–O–B′–O–B exchange interaction mediated by itinerant electrons. We first focus on theBB′ = FeMo-based doubleperovskites, with Sr2FeMoO6 (TC = 420 K) being the most studied compound. These compounds show metallicbehaviour and low magnetic coercivity. Afterwards, we will focus onB′ = Re compounds, where the significant orbital moment of Re plays a crucial rolein the magnetic properties, for example in the large magnetic coercivityand magnetostructural coupling. More specifically, we first discuss theA2FeReO6 series, withmaximum TC = 520 K for Ca2FeReO6, which shows a tendency to semiconducting behaviour. Finally, we describe theSr2(Fe1−xCrx)ReO6 series, withmaximum TC = 625 Kfor Sr2CrReO6, which isthe highest TC in an oxide compound without Fe. This compound is metallic. We discuss the impact ofthese materials for spin electronics in the light of their high spin polarization atthe Fermi level and metallicity. In particular, we focus on the large intergrainmagnetoresistance effect observed in polycrystalline samples and the possibleimplementation of these materials as electrodes in magnetic tunnel junctions.