The Heusler family of materials is intensively studied owing to the strong coupling between the structural, magnetic and electronic degrees of freedom that gives rise to a great variety of phenomena and functional properties, including magnetic shape memory, caloric effects, magnetoresistance effect, giant magnetothermal conductivity and exchange bias effect [1]. The Ni-Mn-based subclass of Heusler compounds features both a first-order magneto-structural and a second-order magnetic transition near room temperature, making it particularly attractive for thermo-magnetic and magnetic shape-memory applications.

In this work we examine the Ni_1.92Mn_1.44[Sn_xIn_1-x]_0.64 series [2] with Density Functional Theory (DFT) simulations, Nuclear Magnetic Resonance (NMR) and Neutron Scattering experiments [3]. We describe the electronic structure details that govern the magnetic transition observed at room temperature, showing that the fate of the magnetic ground state is controlled by competing long and short range interactions. These can be fine-tuned by acting on the valence electron count and on the subtitutional Mn occupying the Ni site. The computational results are also used to support the interpretation of NMR and neutron scattering data, eventually providing an accurate magnetic phase diagram for the series.

[1] K. Ullakko, et al, Appl. Phys. Lett. 69, 1966 (1996); J. Liu, et al., Nat. Mater. 11, 620 (2012); L. Mañosa, et al., Nat. Mater. 9, 478 (2010); B. Zhang, et al., Appl. Phys. Lett. 91, 1 (2007); S. Y. Yu, et al., Appl. Phys. Lett. 90, 88 (2007).
[2] G. Cavazzini, et al., Scr. Mater. 170, 48 (2019).
[3] F. Cugini et al., submitted to PRL.