Thermal Stability, Blocking Regime and Superparamagnetic Behavior in Mn-Al-C Melt Spun Ribbons

Abstract

Alloys possessing nominal compositions Mn53Al45C2 and Mn52Al46C2 were prepared by the melt spinning method and were subjected to complex structural, morphological and magnetic investigations. As these alloys can exhibit tetragonal L10-type and τ phase, they have good potential as rare earth (RE)—free magnets. It is, therefore, important to monitor the ε–τ phase transformation and the stability and the magnetic features of the tetragonal phase in an entire temperature interval. By using synchrotron X-ray diffraction, it has been proven that the ε–τ phase transformation occurs gradually, with the τ phase becoming predominant only after 450 °C. Moreover, this phase has been proven to be quite stable without any grain growth even at the highest temperature investigated at 800 °C. Low temperature behavior was thoroughly investigated by using a complex combination of major and minor hysteresis loops combined with the zero field cooled-field cooled magnetization protocols (ZFC-FC). Two different regimes, blocking and superparamagnetic, were documented. A spin reorientation transition was proven to occur at 55 K while a maximum magnetization observed in ZFC-FC curves proved that at about 75 K, a transition from ferro to superparamagnetic state occurs. The existence of a blocking regime below 55 K that is characteristic to nanogranular systems with superparamagnetic behavior has shown further development towards obtaining RE-free magnets.

Multifunctional Magnetic Nanocomposites: Innovative Processing and Applications

“…Alina Crisan et al reported on the synthesis, morpho-structural characterization, thermal stability and superparamagnetic behavior of Mn–Al–C melt-spun ribbons [ 8 ]. It is well known that the Mn–Al binary alloy has recently attracted significant interest as a potential solution for low-cost, rare-earth-free, permanent magnets.…”

“…While different phases can appear in Mn–Al or Fe–Pt alloys, and only one type is effective for hard magnetic properties, it becomes interesting to monitor the phase transformation and phase stability in Mn–Al melt-spun ribbons (whose degrees of freedom are additionally increased by the third element, C) with respect to processing conditions and thermal treatments. Finally, the magnetic behavior in correlation to structural changes and phase composition and stability was reported in [ 8 ].…”