Dependence of band gaps in d-electron perovskite oxides on magnetism

In addition to the well-known dependence of band gaps of compounds on crystal symmetry and the orbital character of the constituent atoms, d-electron perovskites manifest an additional dependence of gaps on the magnetic spin configuration, a dependence deciding both metal-insulator transitions and magnetic application. We find via electronic structure theory that the factors that explicitly connect gapping magnitudes to magnetism depend on the nature of the band edge orbital character (BEOC) and scale with the number of antiferromagnetic contacts zi between neighboring transition metal ions. The dependence is weak when the BEOC is (d,d*)-like (???Mott insulators???), whereas this dependence is rather strong in (p,d*)-like BEOC (???charge-transfer??? insulators). These rather unexpected rules are traced to the reduced magnitude of interorbital interactions as the number of antiferromagnetic contacts zi increases. In addition to these direct connections between magnetism and gaps, magnetic order also feeds back indirectly into the gapping problem by controlling the propensity of the lattice to develop lattice distortion. Such electronic instabilities toward Jahn-Teller distortions or bond disproportionation feed back into trends in band gap magnitudes. These results highlight the importance of establishing the appropriate magnetic order in the electronic structure theory for reliable rendering of gap-related phenomena such as doping, transport, metal-insulator transitions, and conductive interfaces.

Automated summary

In addition to crystal symmetry and orbital character, the band gaps of d-electron perovskites also depend on the magnetic spin configuration, particularly the nature of the band edge orbital character (BEOC) and the number of antiferromagnetic contacts between neighboring transition metal ions. These dependence rules are traced to the interorbital interactions and play a significant role in understanding phenomena related to band gaps.