Magnetic Properties of Transition Metal Impurities in MgO.

ALEJANDRO FERRÓN; JHON W. GONZÁLEZ; FERNANDO DELGADO; JOAQUÍN FERNANDEZ-ROSSIER

Ciudad Real

Congreso; VIII Edición de la Reunión Bienal del Grupo Especializado de Física del Estado Sólido de la Real Sociedad Española de Física (GEFES 2014); 2014

Real Sociedad Española de Física

P { margin-bottom: 0.08in; } Motivated by the great interest in MgO based tunnel barriers with large magnetoresistance, we study the impact of magnetic dopants in MgO. Specifically, we consider the case of transition metal impurities (Mn, Fe, Co) replacing Mg atoms. We theoretically analyze the magnetic properties of the Mg31O32X bulk (64 atoms unit cell), where X is a transition metal (Mn, Fe or Co). Calculations based on Density-Functional Theory (DFT) were performed using the projector augmented wave (PAW) and generalized gradient approximation (GGA) exchange-correlation functional as implemented in Quantum Espresso code. We perform DFT calculations and we derive a tight-binding model with the aim of understanding the effects of the transition metals in the magnetic properties of the system. The basis set used to obtain the tight-binding Hamiltonian is provided by the maximally localized Wannier functions (MLWF) generated from the DFT calculations using the Wannier 90 package. Our calculations show that the Mg31O32X has a quantized magnetic moment (S=5/2 for X=Mn, S=2 for X=Fe and S=3/2 for X=Co) localized in the dopants atoms. We also analyze the d level splitting of the flat bands introduced by the transition metal atoms inside the MgO gap. A multi-orbital single site Anderson model is build using the tight-binding Hamiltonian obtained from DFT and extended to include spin orbit coupling. The exact numerical diagonalization of the Anderson model yields the effective single ion spin Hamiltonian for the transition metals in the cubic environment of the MgO.