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

Alina Daniela Crisan,Ovidiu Crisan,Aurel Leca,Ioan Dan

doi:10.3390/nano11112898

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.

Highlights

As an intermetallic binary alloy, Mn-Al has attracted a long lived interest ever since the work of H
Evolutions of the magnetic behavior andboth structural, morphologic and magnetic measurements in order to monitor both the stability tetragonal phase stability were well documented over a wide range of temperatures by and the magnetic behavior of Mn-Al-C
The evolution of the structural ε–τ phase transformation has been monitored up to 800 ◦ C by using synchrotron X-ray diffraction, and this technique was proven to be very effective in the estimation of the relative abundance of the tetragonal phase formed during the transformation

Summary

Introduction

As an intermetallic binary alloy, Mn-Al has attracted a long lived interest ever since the work of H. As a potential breakthrough solution for the low cost, rare earth free magnetic materials, the Mn-Al system has attracted a growing interest only recently, expressed by an ever growing number of publications [2,3,4,5,6,7,8,9,10]. MnAl alloy upon annealing can become ferromagnetic in certain conditions depending on the relative stoichiometry of the two elements. Proceeding further, a third alloying element has been added in a number of scientific works in order to increase either its degree of ordering and refine the alloy microstructure or the overall magnetic properties. Mn-Al has certain potential in developing reasonable coercive fields and large specific magnetization

Methods

Results

Discussion

Conclusion