Phase evolution, structure, and magnetic characterization of mechanosynthesized Ni40Fe30Co30 medium-entropy alloy

• Published in: Journal of magnetism and magnetic materials Vol. 489; p. 165466
• Main Authors: Jayaraman, T.V., Thotakura, G.V., Rathi, A.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01-11-2019; Elsevier BV
• Subjects: Alloy powders; Alloys; Cobalt; Coercivity; Cryogenic temperature; Cryogenic treatment; Entropy; Ferromagnetism; Gamma phase; Grain size; Heat treatment; Intrinsic coercivity; Iron; Lattice parameter; Magnetic alloys; Magnetic moments; Magnetic properties; Magnetic saturation; Mechanical alloying; Medium entropy alloys; Ni40Fe30Co30 alloy; Nickel; Particle size; Saturation magnetization; Structural analysis; Lattice parameter; Particle size; Intrinsic coercivity; Mechanical alloying; Ni40Fe30Co30 alloy; Saturation magnetization
• ISSN: 0304-8853; 1873-4766
• DOI: 10.1016/j.jmmm.2019.165466

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•Successfully synthesized nanocrystalline Ni40Fe30Co30 alloy powder.•Ni40Fe30Co30 exhibited magnetic properties similar equiatomic NiFeCo.•The medium-entropy alloy is a suitable precursor for magnetic high-entropy alloys.
This research investigation demonstrates that Ni40Fe30Co30 medium-entropy alloy is a suitable starting ternary composition of ferromagnetic Ni, Fe, and Co, along with the widely explored equiatomic NiFeCo, for designing high-entropy magnetic alloys. Mechanical alloying of the 40 at.% Ni, 30 at.% Fe, and 30 at.% Co powder mixture for 9 h produced Ni40Fe30Co30 alloy, comprised of γ phase. The lattice-parameter, average particle size, and grain size were estimated to be ~0.3580 nm, ~4 μm, and ~8 nm, respectively. At 300 K, the HCI (intrinsic coercivity) and MS (saturation magnetization) of the as-prepared alloy was 2.40 ± 0.09 kA/m and 130.8 ± 2.6 Am2/kg, respectively. At cryogenic temperatures, with the decrement in temperature (T) from 300 K to 60 K, both HCI and MS increased, by ~1.5 times and ~7%, respectively. The estimated HCI(0) (i.e., HCI at 0 K), MS(0) (i.e., MS at 0 K), and μH (maximum magnetic moment per atom) were ~4.09 kA/m, ~140.7 Am2/kg, and ~1.46 μB, respectively. At T < ~660 K, the as-prepared alloy powder maintained the γ phase, and at higher T, α phase precipitated out. MS decreased from 130.8 Am2/kg to 114.9 (±2%) Am2/kg while HCI decreased from 2.40 kA/m to 1.16 ± 0.13 kA/m with the increase in T from 300 K to 840 K. Thermal-treatment improved the soft-magnetic properties of the alloy—MS increased by 10% and HCI decreased by 35%. At cryogenic temperatures, the thermally-treated alloy exhibited magnetic behavior similar to the as-prepared alloy—both HCI and MS increased with the decrease in T.