Spin state and phase competition in TbBaCo₂O₅.₅ and the lanthanide series LnBaCo₂O₅₊δ (0<=δ<=1)

الأصل · EN

A clear physics picture of TbBaCo₂O₅.₅ is revealed on the basis of density functional theory calculations. An antiferromagnetic (AFM) superexchange coupling between the almost high-spin Co³⁺ ions competes with a ferromagnetic (FM) interaction mediated by both p-d exchange and double exchange, being responsible for the observed AFM-FM transition. And the metal-insulator transition is accompanied by an xy/xz orbital-ordering transition. Moreover, this picture can be generalized to the whole lanthanide series, and it is predicted that a few room-temperature magnetoresistance materials could be found in LnBa₁₋ₓAₓCo₂O₅₊δ (Ln=Ho,Er,Tm,Yb,Lu; A=Sr,Ca,Mg).