Regensburg 2013 – scientific programme

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MA: Fachverband Magnetismus

MA 28: Magnetic Materials

MA 28.7: Talk

Wednesday, March 13, 2013, 16:45–17:00, H22

Ab initio study of thermodynamic, electronic, magnetic, structural, and elastic properties of Ni₄N allotropes — Pavlina Hemzalova^1,2,3, •Martin Friak^1,3,4, Mojmir Sob^2,3,4, Alexander Udyansky¹, Duancheng Ma¹, and Joerg Neugebauer¹ — ¹Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf, Germany — ²Masaryk University, Brno, Czech Republic — ³Central European Institute of Technology, CEITEC MU, Brno, Czech Republic — ⁴Institute of Physics of Materials, Academy of Sciences of the Czech Republic, Brno, Czech Republic

We have used density functional theory calculations to study thermodynamic, structural, elastic, and electronic properties of Ni₄N, that forms e.g. when nitriding Ni-containing alloys, in eight different crystallographic phases. In agreement with the experimental findings, the cubic structure with Pearson symbol cP5, space group Pm-3m (221), is found to be the most stable. We determine structural parameters, internal degrees of freedom, bulk moduli and their pressure derivatives for all eight allotropes. The thermodynamic stability and bulk modulus is shown to be anti-correlated. Comparing ferromagnetic and nonmagnetic states, we find common features between the magnetism of elemental Ni and studied ferromagnetic Ni₄N structures. For cubic allotropes, we predict single-crystalline elastic constants, their area moduli, and homogenized polycrystalline elastic moduli. We demonstrate that the elastic anisotropy of the ground-state Ni₄N is qualitatively opposite to that in the elemental Ni. One of the studied metastable cubic phases is found auxetic, i.e. exhibiting negative Poisson ratio.