GE-05: Low-temperature antiferromagnetism in quaternary Mn2FeSi0.5Al0.5 alloys

Manganese-based full- and half-Heusler alloys are often studied because of their interesting antiferromagnetic properties. Currently, the complex physical characterization of ternary Mn2FeSi and Mn2FeAl alloys revealed not only antiferromagnetism at low temperatures, but also complicated microstructure affecting their potential applications in spintronics [1]. Mn2FeSi exhibits crystalline L21 or XA Heusler structure pointing to the half-metallicity behavior, while Mn2FeAl crystallizes in geometrically frustrated cubic β-Mn structure having metallic character of density of electronic states [2]. In this work, the quaternary Mn2FeSi0.5Al0.5 alloys are prepared for the first time in the form of ingots by traditional induction melting technique followed by homogenization annealing for 100 h at 773 K. Their microstructural and magnetic properties are analyzed in detail and compared to the Mn2FeSi and Mn2FeAl alloys. The scanning electron microscopy supplemented by the energy dispersive X-ray (EDX) spectroscopy confirmed uniform distribution of elements and the composition slightly deviated from the nominal one (about 48.5 at.% Mn, 24.6 at.% Fe, 13.9 at.% Si, and 13.0 at.% Al). The results of X-ray diffraction (see Figure 1) revealed the existence of cubic β-Mn structure with the lattice constant 0.6274 nm being slightly lower than that of Mn2FeAl sample (0.6339 nm). The magnetic properties studied in wide temperature range from 5 K to 573 K indicate paramagnetic behaviour at room and elevated temperatures. The transition to antiferromagnetic state occurred at a Néel temperature of 34 K (see Figure 2) and also other magnetic parameters like negative Curie temperature (≈ -700 K) or temperature of irreversibility (≈ 43 K) are comparable to Mn2FeAl ingot. The strong antiferromagnetic spin fluctuation of Mn2FeSi0.5Al0.5 system is caused by the geometric frustration of β-Mn structure (frustration parameter f ≈ 20).References: [1] O. Zivotsky et al., J. Alloys Comp., Vol. 947, p. 169672 (2023) [2] S. Dash et al., J. Magn. Magn. Mater., Vol. 513, p. 167205 (2020)