Anomalous magnetic behaviors of double perovskite R2CrFeO6 (R = rare earth elements) predicted by first-principles calculations

Double perovskite oxide materials have been attracting people's attention for they are good candidates to present large magnetization by either ferromagnetic or ferrimagnetic interactions. Recently, the long debated magnetic ground state of double perovskite La2CrFeO6 is confirmed by experiments to be ferrimagnetic, which is different from the predictions of the Goodenough-Kanamori rules. In order to gain a fundamental understanding of these anomalous magnetic behaviors of double perovskites R2CrFeO6 (R = La, Ce, Pr, Nd, Pm, Sm, Gd, Tb, Dy, Ho, Er, Tm and Y), systematic researches are in need. In this paper, we calculated the structural and magnetic behaviors of double perovskites R2CrFeO6 by first-principles calculations. The effect of the rare-earth ionic radius on crystal structural parameters (e.g., lattice parameters, monoclinic angles, rhombohedral angles, Cr-O-Fe bond angles and filling angles) and magnetic ordering temperature are obtained. Our calculations indicate that the magnetic moments of Fe and Cr in R2CrFeO6 oxides present anti-parallel alignment, i.e., R2CrFeO6 are ferrimagnetic. For all the studied R2CrFeO6 oxides except La2CrFeO6 and Y2CrFeO6, the magnetic ordering temperature decrease linearly with the increase of the rare earth ionic radius, which is different from the previously-observed general magnetic behaviors in various rare earth based perovskites such as R2CrFeO6 and R2CrFeO6. Moreover, it is worth noting that besides generating tilting angles and thus affecting magnetic properties, rare earth ions can also affect the magnetic exchange coupling of the double perovskite R2CrFeO6 systems in other ways. Our work can provide comprehensive information for understanding the anomalous magnetic properties of double perovskite R2CrFeO6 and would be helpful for the development of new multiferroic materials.