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 . 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 TC and a magnetic moment μ ≈ 2.8 μB. 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 TC = 400 K with μ ≈ 1.5 μB with room to increase.
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Prof. i. R. Dr. Mehmet Acet
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