Electronic and magnetic structure of CrO2-RuO2interfaces

Abstract

CrO${}_{2}$ and RuO${}_{2}$ share the same (rutile) crystal structure and have similar lattice constants. We have used density functional theory (DFT) within the generalized gradient approximation (GGA) to calculate the electronic and magnetic structure of CrO${}_{2}$, RuO${}_{2}$, and their interfaces. We also used DFT-GGA to investigate the electronic and magnetic structure of CrO${}_{2}$ and RuO${}_{2}$. Consistent with previous calculations and experiments, we find that the CrO${}_{2}$ Fermi energy lies in a band gap for the minority channel. RuO${}_{2}$, in agreement with experiment, is predicted to be nonmagnetic. We find relatively good matching between the majority of the energy bands of CrO${}_{2}$ and both RuO${}_{2}$ channels in the (100), (110), and (001) directions. For (100) interfaces, we find a small induced Ru moment oriented opposite to that of the Cr moments. We study the change in energy as a function of the angle between the interfacial and bulk Cr magnetic moments. We investigate both sharp and mixed (100)- and (110)-oriented CrO${}_{2}$-RuO${}_{2}$ interfaces with a supercell approach. We investigate the origin of the large negative moment that forms when an Ru ion substitutes for a Cr ion. We speculate that weakened interionic exchange interactions, noncollinear spins, and induced moments at interfaces may be a common problem in oxides that may be a challenge to overcome for achieving large giant magnetoresistance and tunneling magnetoresistance effects.