Structure and Properties Evolutions for Hard Magnetic MnAl and MnGa Based Alloys Prepared by Melt Spinning or Mechanical Milling

Abstract

Mn-based alloys are generally thought to be the potential rare earth free permanent magnets with acceptable magnetic properties due to its available high magnetization and anisotropy field. In this work, MnAl and MnGa based alloys have been investigated regarding to their processing, structures and magnetic properties. MnAl based alloys with various C additions and/or trace rare earth doping were prepared by melt spinning. The phase transitions during rapid quenching and post annealing were investigated. The composition and annealing process dependent magnetic properties were obtained. The anisotropic MnAlC flakes with improved magnetic properties were also fabricated by surfactant assisted ball milling using alloy ingot as the precursor. The effects of ball milling and post annealing processes on the phase structure and magnetic properties were discussed. As for Mn-Ga alloy, Mn 70 Ga 30 binary alloy were prepared by melt spinning followed by post heat treatment. The preliminary results show relatively high coercivity. In addition, the prospect of MnAl and MnGa based alloys for permanent magnet applications were discussed in this paper.

Formation of pure $$\tau$$-phase in Mn–Al–C by fast annealing using spark plasma sintering

“…2(a,b)) and after conventional annealing for 30 min at 500 C, we obtain single s-phase. The transformation is not completed when lower dwelling times are used, consistent with the literature [18,[27][28][29]. By increasing the temperature to 550 C , one can obtain single s-phase in 5 min with conventional annealing.…”

Structural, magnetic and magneto-optical studies of Mn/Al bilayer thin films on GaAs substrates

“…Annealing above 500 °C was not performed in this study because of the reduction in the ferromagnetic τ-phase as already reported for annealing temperatures ≥ 550 °C. 26,27 The XRD patterns for MnAl_400_1h and MnAl_400_2h films annealed for different times are shown in Fig. 3 , which revealed that the τ (100) and τ (101) peaks present in the MnAl_400_1h film were diminished in the MnAl_400_2h film.…”

“… 25 On further increasing the temperature from 550 °C to 600 °C, the τ-phase decomposed into non-magnetic γ and β phases. 26,27 Previous studies revealed that ferromagnetic ordering was enhanced in the MnAl thin films on increasing the annealing temperature to 500 °C. 27,28 Therefore, we selected the temperature range from 300 to 500 °C to achieve the desired ferromagnetic phase.…”

“…The ferromagnetic s-phase of MnAl is typically achieved by controlled the cooling of the 3-phase or by quenching followed by annealing at 300-550 C. 25 On further increasing the temperature from 550 C to 600 C, the s-phase decomposed into non-magnetic g and b phases. 26,27 Previous studies revealed that ferromagnetic ordering was enhanced in the MnAl thin lms on increasing the annealing temperature to 500 C. 27,28 Therefore, we selected the temperature range from 300 to 500 C to achieve the desired ferromagnetic phase. Our results are consistent with previous studies 25,27,28 and suggest the enhancement of the ferromagnetic s-phase in MnAl thin lm up to the annealing temperature of 500 C. Annealing above 500 C was not performed in this study because of the reduction in the ferromagnetic s-phase as already reported for annealing temperatures $ 550 C. 26,27 The XRD patterns for MnAl_400_1h and MnAl_400_2h lms annealed for different times are shown in Fig.…”

Structural, microstructural and magnetic evolution in cryo milled carbon doped MnAl

“…Cryo milling increases the potential capability of aligning the crystals along the easy magnetization axis, without the creation of sheet-like particles with random orientation, as previously observed when milling is done at ambient temperatures 25 , 28 . However, for this to be a viable route, single crystal grains (or particles with correspondingly aligned grains) are necessary.…”