Enhancement of Fe magnetic moments in ferromagnetic Fe16N2.

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In order to investigate the electronic and magnetic properties of an ${\mathrm{Fe}}_{16}$${\mathrm{N}}_{2}$ ferromagnet, we have performed electronic-structure calculations employing the total-energy self-consistent local-density-functional linearized muffin-tin orbital band method. Band structures, density of states, Stoner parameters, magnetic moments, and cohesive bonding properties for paramagnetic or ferromagnetic ${\mathrm{Fe}}_{16}$${\mathrm{N}}_{2}$ are obtained. The effect of spin-orbit interaction on the magnetism is also explored. Based on these results, the magnetic structure and the microscopic origin of the enhancement of Fe magnetic moments in this compound are investigated. Magnetic moments of three types of Fe [Fe(I), Fe(II), and Fe(III)] in ${\mathrm{Fe}}_{16}$${\mathrm{N}}_{2}$ are 2.13, 2.50, and 2.85${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, respectively. Large enhancement of the magnetic moment is observed in Fe(II) and Fe(III), which are located farther from N than Fe(I). This suggests that the local environment plays a very important role in determining the Fe magnetic moments in this compound. The orbital contribution to the magnetic moment in Fe atoms is minor, a total of 0.56${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ in the unit cell. Our value of the average magnetic moment per Fe atom, 2.50${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, is a bit smaller than the reported value, \ensuremath{\sim}3.0${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$, estimated from the experiment.