Comparative studies on the room-temperature ferrielectric and ferrimagnetic Ni3TeO6-type A2FeMoO6 compounds (A = Sc, Lu)

First-principles calculations have been carried out to study the structural, electric, and magnetic properties of Ni3TeO6-type A2FeMoO6 compounds (A = Sc, Lu). Their electric and magnetic properties behave like room-temperature ferrielectric and ferrimagnetic insulators where polarization comes from the un-cancelled antiparallel dipoles of (A(1), Fe(3+)) and (A(2), Mo(3+)) ion groups, and magnetization from un-cancelled antiparallel moments of Fe(3+) (d(5)) and Mo(3+) (d(3)) ions. The net polarization increases with A's ionic radius and is 7.1 and 8.7 μCcm(-2) for Sc2FeMoO6 and Lu2FeMoO6, respectively. The net magnetic moment is 2 μB per formula unit. The magnetic transition temperature is estimated well above room-temperature due to the strong antiferromagnetic superexchange coupling among Fe(3+) and Mo(3+) spins. The estimated paraelectric to ferrielectric transition temperature is also well above room-temperature. Moreover, strong magnetoelectric coupling is also anticipated because the magnetic ions are involved both in polarization and magnetization. The fully relaxed Ni3TeO6-type A2FeMoO6 structures are free from soft-phonon modes and correspond to stable structures. As a result, Ni3TeO6-type A2FeMoO6 compounds are possible candidates for room-temperature multiferroics with large magnetization and polarization.