Intra-chain superexchange couplings in quasi-1D 3d transition-metal magnetic compounds

Abstract

The electronic structure and magnetic properties of the quasi-1D transition-metal borates PbMBO4 (M = Ti, V, Cr, Mn, Fe, Co) have been investigated by density functional theory, including electronic correlation. The results evidence PbCrBO4 and PbFeBO4 as antiferromagnetic (AFM) semiconductors (intra-chain AFM and inter-chain FM) and PbMnBO4 as a ferromagnetic (FM) semiconductor (both intra- and inter-chain FM) in accordance with experimental observations. For non-synthesized PbTiBO4, PbVBO4, and PbCoBO4, the ground-state magnetic structures are paramagnetic, FM, and paramagnetic, respectively. In this series of compounds, there are two kinds of superexchange couplings dominating their magnetic properties, i.e. the direction M–M delocalization superexchange and indirect M–O–M correlation superexchange. For PbMBO4 with M3+ d n, n ⩽ 3 (M = V and Cr), the main intra-chain spin coupling is the M–M t2g–t2g direct delocalization superexchange, while for PbMBO4 with M3+ d n, n > 3 (M = Mn and Fe), the main intra-chain spin coupling is the near 90° M–O–M eg–p–eg indirect correlation superexchange.