Possible d0 ferromagnetism in MgO doped with nitrogen

TL;DR

This study investigates the potential for d0 ferromagnetism in nitrogen-doped MgO using quantum Monte Carlo simulations, revealing local magnetic moments and long-range ferromagnetic correlations influenced by impurity states.

Contribution

It introduces a theoretical model for nitrogen-doped MgO and demonstrates the presence of ferromagnetic correlations and their temperature dependence, a novel insight into d0 ferromagnetism.

Findings

Finite local magnetic moments observed for N impurities.

Long-range ferromagnetic correlations between N impurities.

Temperature-dependent exchange interactions similar to other diluted magnetic semiconductors.

Abstract

We study the possibility of d0 ferromagnetism in the compound MgO doped with nitrogen (N). The Haldane-Anderson impurity model is formulated within the tight-binding approximation for determining the host band-structure and the impurity-host hybridization. Using the quantum Monte Carlo technique, we observe a finite local moment for an N impurity, and long-range ferromagnetic correlations between two N impurities. The ferromagnetic correlations are strongly influenced by the impurity bound state. When the ferromagnetic correlation between a pair of impurities is mapped onto the isotropic Heisenberg model for two spin-1/2 particles, the effective exchange constant J12 is found to increase with increasing temperature. Similar temperature dependence of J12 is also obtained in other diluted magnetic semiconductors, such as zincblende ZnO doped with Mn. The temperature dependence of J12 suggests that the mapping of the full Hamiltonian onto the spin Hamiltonian cannot fully describe the magnetic correlations for the diluted magnetic semiconductors at least in the limit of low impurity spin.