Magnetic interactions in transition metal doped ZnO : An abinitio study

TL;DR

This study uses density functional theory to explore magnetic interactions in transition-metal doped ZnO, revealing how different dopants and defects influence magnetic states and the importance of computational details.

Contribution

It provides a comprehensive ab initio analysis of magnetic interactions in doped ZnO, highlighting the effects of correlation treatments and defect configurations on magnetic ordering.

Findings

Ferromagnetic coupling can occur in some cases with LSDA.

LSDA+U often favors antiferromagnetic states over ferromagnetic.

Oxygen vacancies consistently favor antiferromagnetic ordering.

Abstract

We calculate the nature of magnetic interactions in transition-metal doped ZnO using the local spin density approximation and LSDA+\textit{U} method of density functional theory. We investigate the following four cases: (i) single transition metal ion types (Cr, Mn, Fe, Co, Ni and Cu) substituted at Zn sites, (ii) substitutional magnetic transition metal ions combined with additional Cu and Li dopants, (iii) substitutional magnetic transition metal ions combined with oxygen vacancies and (iv) pairs of magnetic ion types (Co and Fe, Co and Mn, etc.). Extensive convergence tests indicate that the calculated magnetic ground state is unusually sensitive to the k-point mesh and energy cut-off, the details of the geometry optimizations and the choice of the exchange-correlation functional. We find that ferromagnetic coupling is sometimes favorable for single type substitutional transition metal ions within the local spin density approximation. However, the nature of magnetic interactions changes when correlations on the transition-metal ion are treated within the more realistic LSDA + \textit{U} method, often disfavoring the ferromagnetic state. The magnetic configuration is sensitive to the detailed arrangement of the ions and the amount of lattice relaxation, except in the case of oxygen vacancies when an antiferromagnetic state is always favored.