Observation of charge transfer induced large enhancement of magnetic moment in a structurally disordered inverse Heusler alloy Fe2RuGe

We report the successful synthesis of a new 4d-based polycrystalline inverse Heusler alloy Fe2RuGe by an arc melting process and have studied in detail its structural, magnetic and transport properties complemented with first-principles calculations. X-ray and neutron diffraction, extended x-ray absorption fine structure, and 57Fe Mössbauer spectroscopic studies confirm the single-phase nature of the system where the Fe and Ru atoms are randomly distributed in the 4c and 4d Wyckoff positions in a ratio close to 50:50. The formation of the disordered structure is also confirmed by the theoretical energy minimization calculation. Despite the random cross-site disorder of Fe and Ru atoms, magnetic measurements suggest not only a high Curie temperature of ∼860 K, but also a large saturation magnetic moment ∼4.9µB per formula unit at 5 K, considerably exceeding the theoretical limit (4 µB per formula unit) predicted by the Slater-Pauling rule. Only a few Fe-based inverse Heusler alloys are known to exhibit such high Curie temperatures. Neutron diffraction analysis coupled with the isothermal magnetization value indicates that the magnetic moments in Fe2RuGe are associated with Fe atoms only, which is also confirmed by Mössbauer spectrometry. Interestingly, in comparison to the cubic or hexagonal phase of the parent compound, Fe3Ge, the Curie temperature of Fe2RuGe has increased significantly despite the substitution of the nonmagnetic yet isoelectronic element Ru in this structurally disordered compound. Our theoretical calculation reveals that the large Fe moment (∼2.8µB/Fe) on the 4b site can be attributed to a charge transfer from this Fe site towards its Ru neighbors while a significant moment (∼2µB/Fe) is kept on the other Fe sites. Instead of expected Slater-Pauling value of 4µB/f.u., the substantially increased observed total magnetic moment of ∼4.9µB/f.u. is due to these electron charge transfers, which have not been previously reported in other ferromagnetic Heusler systems. © 2024 American Physical Society.

Keywords

Heusler alloys, Atoms, Radon, Curie point, Calculation methods, Order-disorder model, Iron

Citation

Chakraborty, S., Gupta, S., Bhasin, V., Pakhira, S., Barreteau, C., Crivello, J.-C., Jha, S. N., Bhattacharyya, D., Avdeev, M., Paul-Boncour, V., Greneche, J.-M., Alleno, E., & Mazumdar, C. (2023). Observation of charge transfer induced large enhancement of magnetic moment in a structurally disordered inverse Heusler alloy Fe2RuGe. Physical Review B, 108(24), 245151. https://doi.org/10.1103/PhysRevB.108.245151