Influence of Heat Treatment on the Microstructure and Magnetic Properties of Mn–Sn–Co–N Alloys

Abstract

This paper describes the influence of heat treatment on the microstructure and magnetic properties of Mn–Sn–Co–N alloys. After homogenization at 950°C for 20 h in Ar, Mn_82.5Sn₁₀Co_7.5 alloys were annealed at 900°C for 1–20 h in N₂ and quenched to room temperature (first-annealing). The alloys were subsequently annealed at 400–700°C for 5 h in N₂ and quenched to room temperature (second-annealing). The coercivity of the alloys changed drastically by the second annealing. The samples subjected to second annealing at 500°C showed maximum coercivity of 1270 kAm⁻¹ and exhibited a fine two-phase microstructure. Wavelength Dispersive X-ray Spectrometer (WDS) and X-ray Diffraction (XRD) analyses revealed that the fine two-phase microstructure consists of β-Mn and perovskite-type (Mn₄N-like) phases, as well as that the two phases emerged from the ζ′ phase during the second-annealing at 500°C.