Inducing strong magnetism in high-entropy alloys by exploiting their anti-Invar properties

Mixing numerous 3d-elements and subsequently melting them together or allowing them to undergo a solid-state reaction gives rise to random solid solutions with a high configurational entropy [1]. The classical example is the Cr₂₀Fe₂₀Mn₂₀Fe₂₀Co₂₀Ni₂₀ alloy with a 20% equiatomic composition forming a single FCC phase. It is paramagnetic at room temperature and has competing interactions at low temperatures [2,3]. This material has a valence electron concentration (e/a) = 8, which corresponds to that of elemental Fe, but instead of being BCC it is FCC. FCC-Fe has an enhanced anharmonicity known as anti-Invar. If FCC Fe could have been expanded, it would have been ferromagnetic with a high Curie temperature T_C and a magnetic moment μ ≈ 2.8 μ_B. We show here first that Cr₂₀Fe₂₀Mn₂₀Fe₂₀Co₂₀Ni₂₀ can indeed be expanded by introducing carbon. We introduce carbon into the octahedral sites of this material and maintain (e/a) = 8 to obtain Cr₁₆Fe₁₆Mn₁₆Fe₁₆Co₁₆Ni₁₆C₂₀. This becomes FM with a Curie temperature T_C = 400 K with μ ≈ 1.5 μ_B with room to increase.

References:

[1] J. Yeh, et al., Adv. Eng. Mater. 6, 299-303 (2004).
[2] Y. P. Wang, B. S. Li, H. Z. Fu, Adv. Eng. Mater. 11, 641 (2009)
[3] O. Schneeweiss, et al., Phys. Rev. B 96, 014437 (2017).

Prof. i. R. Dr. Mehmet Acet

Experimentalphysik

Universität Duisburg-Essen

47048 Duisburg

Phone	+49 203 37-92023
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	Team Prof. Dr. M. Farle "Structure and Magnetism of nanoscale systems"
	Universität Duisburg-Essen