Density functional theory study of vacancy induced magnetism in Li${}_3$N

Abstract

The effect of lithium vacancies in the hexagonal structure of $\hat{I}\pm -$Li${}_3$N, is studied within the framework of density functional theory. Vacancies ($\square$) substituting for lithium in $\hat{I}\pm -$Li${}_2$(Li${}_{1-x}{\square }_x$)N are treated within the coherent potential approximation as alloy components. According to our results long range N($p$)-ferromagnetism ($\sim 1$ $\hat{I}{¼}_B$) sets in for vacancy substitution within the [Li${}_2$N] layers ($x\ge 0.7$) with no significant change in unit cell dimensions. By total energies differences we established that in-plane exchange couplings are dominant. Vacancies substituting inter-plane Li, leads to a considerable structural collapse ($c/a\approx 0.7$) and no magnetic moment formation.