Magnetic properties of Fe₂GeMo₃N

A polycrystalline sample of Fe2GeMo3N has been synthesized by the reductive nitridation of a mixture of binary oxides in a flow of 10% dihydrogen in dinitrogen. The reaction product has been studied by magnetometry, neutron diffraction and Mossbauer spectroscopy over the temperature range 1.8 <= T/K <= 700. The electronic structure and magnetic coupling have been modelled by Density Functional Theory (DFT) and Monte Carlo methods. Fe2GeMo3N adopts the cubic eta-carbide structure with a = 11.1630(1) angstrom at 300 K. The electrical resistivity was found to be similar to 0.9 m Omega cm over the temperature range 80 <= T/K <= 300. On cooling below 455 K the compound undergoes a transition from a paramagnetic to an antiferromagnetic state. The magnetic unit cell contains an antiferromagnetic arrangement of eight ferromagnetic Fe-4 tetrahedra; the ordered atomic magnetic moments, 1.90(4) mu(B) per Fe atom at 1.8 K, align along a < 111 > direction. DFT predicts an ordered moment of 1.831 mu(B) per Fe. A random phase approximation to the DFT parameterised Heisenberg model yields a Neel temperature of 549 K, whereas the value of 431 K is obtained in the classical limit for spin. Monte Carlo calculations confirm that the experimentally determined magnetic structure is the lowest-energy antiferromagnetic structure, but with a lower Neel temperature of 412 K. These results emphasise the potential of these computational methods in the search for new magnetic materials.