Evidence of exchange coupling in τ-MnAlC/FeCo system

The τ-MnAlC/FeCo system has potential to be applied as rare earth-free permanent magnet, due to exchange coupled between hard and soft magnetic phases as alternative for the development of high energy product permanent magnets. In this work the hard-magnetic phase Mn_53.3Al₄₅C_1.7 (μ₀H_c = 0.37 T of coercive force, M_r = 23.52 Am²/kg of remanent magnetization, M_s = 52.94 Am²/kg of saturation magnetization and (BH)_max = 3.89 kJ/m³ of maximum energy product) was mixed with the soft magnetic phase Fe₆₅Co₃₅ (μ₀H_c = 0.007 T and M_s = 221.33 Am²/kg) using a solid-state procedure. The magnetic materials were sintered using different ratios of hard and soft magnetic phases: 95:5, 90:10, 85:15 and 80:20; and different sintering temperatures (300, 400, 500 and 600 °C) in order to improve the magnetic properties. The magnetic exchange coupling between MnAlC and FeCo was proved by the hysteresis loop and its corresponding Thamm-Hesse analysis. The best result was obtained for MnAlC/FeCo (95/5 wt%) sintered at 500 °C during 30 min, for which the magnetic properties were μ₀H_c = 0.277 T, M_s = 76.43 Am²/kg and (BH)_max = 5.57 kJ/m³.