Saha-Dasgupta Tanusri, Pradhan Koushik
Department of Condensed Matter Physics and Materials Science S. N. Bose National Centre for Basic Sciences, Kolkata 70098, India.
J Phys Condens Matter. 2024 Oct 18;37(2). doi: 10.1088/1361-648X/ad841a.
One of the most important phenomena in magnetism is the exchange interaction between magnetic centres. In this topical review, we focus on the exchange mechanism in transition-metal compounds and establish kinetic-energy-driven two-sublattice double-exchange as a general mechanism of exchange, in addition to well-known mechanisms like superexchange and double exchange. This mechanism, which was first proposed (Sarma20002549), in the context of SrFeMoO, a double-perovskite compound, later found to describe a large number of 3d and 4d or 5d transition metal-based double perovskites. The magnetism in multi-sublattice magnetic systems like double-double and quadrupolar perovskites involving 3d and 4d or 5d transition-metal ions have also been found to be governed by this as a primary mechanism of exchange. For example, the numerical solution of a two-sublatice double exchange with additional superexchange couplings for the FeRe-based double double and quadrupolar perovskites are found to reproduce the experimentally observed magnetic ground state as well as the high transition temperature of above 500 K. The applicability of this general mechanism extends beyond the perovskite crystal structures, and oxides, as demonstrated for the pyrochlore oxide, TlMnOand the square-net chalcogenides KMnX(X = S, Se, Te). The counter-intuitive doping dependence and pressure effect of magnetic transition temperature in TlMnOis explained, while KMnX(X = S, Se, Te) compounds are established as half-metallic Chern metals guided by two sublattice double exchange. While the kinetic energy-driven two-site double-exchange mechanism was originally proposed to explain ferromagnetism, a filling-dependent transition can lead to a rare situation of the antiferromagnetic metallic ground state, as found in La-doped SrFeMoO, and proposed for computer predicted double perovskites Sr(Ca)FeRhO. This opens up a vast canvas to explore.
