Magnetism-Structure Correlations during the ε→τ Transformation in Rapidly-Solidified MnAl Nanostructured Alloys

Abstract

Magnetic and structural aspects of the annealing-induced transformation of rapidly-solidified Mn 55 Al 45 ribbons from the as-quenched metastable antiferromagnetic (AF) ε-phase to the target ferromagnetic (FM) L1 0 τ-phase are investigated. The as-solidified material exhibits a majority hexagonal ε-MnAl phase revealing a large exchange bias shift below a magnetic blocking temperature T B~9 5 K (H ex~1 3 kOe at 10 K), ascribed to the presence of compositional fluctuations in this antiferromagnetic phase. Heat treatment at a relatively low annealing temperature T anneal ≈ 568 K (295 °C) promotes the nucleation of the metastable L1 0 τ-MnAl phase at the expense of the parent ε-phase, donating an increasingly hard ferromagnetic character. The onset of the ε→τ transformation occurs at a temperature that is ~100 K lower than that reported in the literature, highlighting the benefits of applying rapid solidification for synthesis of the rapidly-solidified parent alloy.

Study of phases evolution in high-coercive MnAl powders obtained through short milling time of gas-atomized particles

“…The structure and magnetic properties of the MnAl system have been widely studied because the microstructural changes and defects introduced during the metastable -phase transformation highly influence its magnetic properties. Studies have reported various techniques to prepare MnAl-based alloys, including hot extrusion, melt spinning, mechanical alloying, mechanical milling (MM), cryomilling, and gas-atomization [8,9,[17][18][19][20][21][22][23]. Ball milling is a well-known technique used for microstructure refinement and strain inducement, but also for promotion of metastable phase formation.…”

Development of permanent magnet MnAlC/polymer composites and flexible filament for bonding and 3D-printing technologies

“…Recently, coercivity development has been managed in MnAl particles through proper optimization of the phases coexisting in the material and induced microstructural strain [ 18,19 ]. The low cost and wide availabilities of Mn and Al in combination with a good machinability, high modulus of elasticity and excellent corrosion resistance complete the characteristics required for making of this material an excellent rare earth-free PM candidate [ 15,20 ]. In addition to all these benefits, MnAl shows a reduced density of 5200 kg/m 3 by comparison with 7600 kg/m 3 for Nd 2 Fe 14 B, which will lead to lighter PMs.…”

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

“…Previous research show that the τ-phase is formed through a two-step process, originating from the parent hexagonal ɛ-phase that transforms into the intermediate B19-structure ɛ’-phase which in turn transforms into the τ-phase if sufficient undercooling is achieved at 723 K < T < 823 K 16 , 17 . These transformations are believed to occur independently of the composition and are controlled by nucleation and growth processes 17 .…”

“…These transformations are believed to occur independently of the composition and are controlled by nucleation and growth processes 17 . It has been shown that the transformation is highly dependent on the nucleation of the τ-phase at the interphase with the ɛ-phase 16 .…”