Chemical ordering in NiMn-based Heusler alloys with magnetostructural phase transition is crucial for understanding the physics of the phase transition. In the new field of all-d-metal Ni(Co)MnTi Heusler alloys, the experimental determination of chemical order is challenging due to the low difference in scattering power of the different elements. Here, we report a combined approach of neutron and x-ray diffraction for an analysis of chemical order in Ni(Co)MnTi alloys and show that no Heusler-typical L21 order between Ti and Mn is present. Furthermore, Co and Ni atoms do not exhibit order among them; however, the phase transition of Co containing samples can be shifted significantly by changing the degree of B2 order with proper heat treatment. Using first-principles calculations, we reveal how the structural and magnetic sub-systems depend on the degree of B2 disorder.
This publication results from a collaboration of CRC/TRR 270 projects A05, B01, B04 (first author) and B06.
D. Koch, B. Beckmann, N. M. Fortunato, O.N. Miroshkina, M. E. Gruner, H. Zhang, O. Gutfleisch, and W. Donner, Journal of Applied Physics 131, 073903 (2022)