Ab initio calculations and synthesis of the off-stoichiometric half-Heusler phase Ni1−xMn1+xSb

Abstract

We perform a combined theoretical and experimental study of the phase stability and magnetism of the off-stoichiometric Ni 1−x Mn 1+x Sb in the half-Heusler crystal phase. Our work is motivated by the need for strategies to engineer the magnetism of potentially half-metallic materials, such as NiMnSb, for improved performance at elevated temperatures. By means of ab initio calculations we investigate Ni 1−x Mn 1+x Sb over the whole composition range 0 Յ x Յ 1 of Ni replacing Mn and show that at relevant temperatures, the half-Heusler phase should be thermodynamically stable up to at least x = 0.20 with respect to the competing C38 structure of Mn 2 Sb. Furthermore we find that half-Heusler Ni 1−x Mn 1+x Sb retains half-metallic band structure over the whole concentration range and that the magnetic moments of substitutional Mn Ni atoms display magnetic exchange interactions an order of magnitude larger than the Ni-Mn interaction in NiMnSb. We also demonstrate experimentally that the alloys indeed can be created by synthesizing off-stoichiometric Ni 1−x Mn 1+x Sb films on MgO substrates by means of magnetron sputtering.

Tunable damping, saturation magnetization, and exchange stiffness of half-Heusler NiMnSb thin films

“…49 A reduction of M S is expected in Mn-rich NiMnSb alloys, due to the antiferromagnetic coupling of the Mn Ni defects to the Mn lattice in the C1 b structure of the half-Heusler material. 29 An even stronger reduction is observed for the Ni-rich sample 1, which is in accordance with the formation of Ni Mn antisites. 50 While the measurement error for M S is comparatively large due to uncertainties in the volume determination, the error bars for M eff , as obtained from ferromagnetic resonance, are negligible.…”

“…High-resolution x-ray diffraction (HRXRD) measurements give information on the structural properties of these samples, confirming the extremely high crystalline quality of all samples with different Mn concentra- tion, even in the far from stoichiometric cases (samples 1 and 6). 15 The vertical lattice constant is found to increase with increasing Mn concentration and, assuming a linear increase, 29 we estimate the difference in Mn concentration across the whole set of samples to be about 40 at. %.…”

Spectral signatures of thermal spin disorder and excess Mn in half-metallic NiMnSb

“…For Mn Ni the antiparallel spin alignment is very stable in agreement with Ref. 36, while the self-consistent solution for the parallel alignment could not be obtained. Fig.…”

“…1(a)), and the broadening of the bands is very small. Since the spin of Mn Ni is strongly coupled to the host magnetization [36], this defect is spectroscopically invisible and can not lead to lowtemperature anomalies.…”

Correlated electronic structure with uncorrelated disorder

“…Several suggestions have been given to explain this large reduction in spin-polarization. Among them we mention electronic correlation effects 52,73 and disorder [74][75][76] .…”