High Coercivity in MnAl Disc Prepared by Severe Plastic Deformation

Abstract

Ping‐Zhan Si et al. (article number http://doi.wiley.com/10.1002/pssb.201900356) have prepared bulk MnAl nanocrystalline alloy with a highest room‐temperature coercivity up to 0.59 T by using a high‐pressure torsion process. The severe plastic deformation process decreased the grain size of τ‐phase MnAl significantly. As a result, the coercivity of the MnAl was enhanced remarkably. This work opens a window for the development of bulk MnAl with high coercivity and enhanced remanence for applications of MnAl‐based magnets. – The cover article is part of the Special Section “Advanced Magnetic Oxides”, comprising one Feature Article and 8 Original Papers (see the Preface, article number http://doi.wiley.com/10.1002/pssb.202000058).

Microstructure and magnetic properties of Mn-Al-C permanent magnets produced by various techniques

“…But it is noticeable the increase of defect density, including polytwinned microstructure with high density of dislocations. The high density of defects, especially dislocations, can hinder the domain wall motion leading to a higher coercivity, in accordance with the magnetic results presented in Figure 8c, and as previous reported by [30,31,41].…”

“…The influence of plastic deformation as well as of crystal defects related to crystals plasticity on the formation magnetic properties of Mn-Al based alloys was intensively studied through recent years [30,31,40,41]. The high pressuretorsion (HPT À Walter Klements GmbH) process was used to compact and deform t-phase Mn-Al-C powder (particle size below 80 mm) into disc shaped samples of 10 mm diameter and 1 mm height.…”

“…Different studies have shown the complex relation between the several types of microstructural defects of t-MnAl phase and the magnetic properties, in terms of remanence, coercivity and, consequently, the BH max value [10,21,[27][28][29][30][31][32]. Among the possible defects in this material system, the existence of twin boundaries is often related to one of the major difficulties to obtainhighly textured samples and improved remanence in Mn-Al magnets [31].…”