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PGI-1 Talk: Dr. Shishir Kumar Pandey

Doping an antiferromagnetic insulator: A route to an antiferromagnetic metallic phase

18 Sep 2019 11:30
Seminar room N-142

National Taiwan University


With the recent studies indicating the possibility of antiferromagnetic spintronics offering more efficient devices, the focus has shifted from ferromagnetic materials to antiferromagnetic materials. One requirement among antiferromagnets are metals, especially examples among the oxide based ones. This would pave the route towards oxide based electronics. A general rule that has emerged by examining the ground states of various magnetic materials is that ferromagnetism is usually accompanied by metallicity while antiferromagnets are insulators. Hence a route, if possible, to antiferromagnetic metals would be useful. We have therefore explored the design principle of doping carriers into an AFM insulator as a route to obtaining AFM metals.

For this purpose, we used a multiband Hubbard model in which the entering parameters correspond to a 3d transition metal oxides as well as a 5d transition metal oxides. Phase diagrams have been obtained in both the cases at various doping concentrations as a function of U on transition metal d states. In the case of the 5d oxide, we show that electron doping in an AFM insulator leads to realization of AFM metallic phase at small U values while at large U, a charge ordered insulating phase was found to be stabilized. In contrast to the 5d case, we found no AFM metallic regime in the phase diagram for 3d transition metal oxides. We show that it is the relative value of exchange splitting with respect to the crystal field splitting which determines the ground state properties.

The role of orbitals degeneracy present in reals materials was found to play an important role in the enhanced stability of the AFM metallic phase found here. In this work we show for the first time the role of Hund’s coupling in determining the magnetism in the metallic phases of the multiband Hubbard model.


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