Density functional theory study of vacancy induced magnetism in Li₃N

The effect of lithium vacancies in the hexagonal structure of $\alpha-$Li$_3$N, is studied within the framework of density functional theory. Vacancies ($\square$) substituting for lithium in $\alpha-$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 ($\sim 1$ $\mu_B$) 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.