Investigation of Possible Half-Metallic Antiferromagnets on Double Perovskites A2BB′O6 (A=Ca, Sr Ba; B,B′=Transition Metal Elements)

A search was made for possible half-metallic (HM) antiferromagnet (AFM) in all the (C-2(29) = 406) double perovskites structures of Sr2BB'O-6 where BB' pairs are any combination of 3d, 4d or 5d transition elements with the exception of La. Sr can also be replaced by Ca or Ba whenever HM-AFM was found and similar calculations were then performed in order to probe further possibilities. It was found that A(2)MoOsO(6), A(2)TcReO(6), A(2)CrRuO(6), where A=Ca, Sr, Ba, are all potential candidates for HM-AFM. The AFM of A(2)BB'O-6 comes from both the superexchange mechanism and the generalized double exchange mechanism via the B(t(2g))-O2p(pi)-B'(t(2g)) coupling, With the latter also being the origin of their HM. Also considered were the effects of spin-orbit coupling (SOC) and correlation (+U) by introducing +SOC and +U corrections. It is found that the SOC effect has much less influence than the correlation effect on the HM property of the compounds. For A(2)TcReO(6) and A(2)CrRuO(6), after +U, they become nearly Mott-Insulators. In the future, it is hoped that there will be further experimental confirmation for these possible HM-AFM candidates.