Superexchange dominates in magnetic topological insulators

It has been suggested that the enlarged spin susceptibility in topological insulators, described by Van Vleck's formalism, accounts for ferromagnetism of bismuth-antimony chalcogenides doped with transition metal impurities. In contrast, earlier studies HgTe and related systems pointed out interband analog Ruderman-Kittel-Kasuya-Yosida interaction (the Bloembergen-Rowland mechanism) leads to antiferromagnetic coupling between pairs localized spins. Here, we critically revisit these two approaches, show their shortcomings, elucidate why magnitude contribution is small even systems. From proposed theoretical approach our computational magnetism Mn-doped CdTe, conclude that, absence band carriers, superexchange dominates, its sign depends on coordination charge state magnetic impurities rather than class host material.