Scanning Hall Probe Imaging of LaFe13-xSix

Abstract

Magnetocaloric materials with a Curie temperature near room temperature are of interest for application in high-efficiency solid state cooling. There are several promising families of materials including the LaFe13-xSix system which offers large magnetocaloric entropy change, low magnetic and thermal hysteresis, and tunability of the metamagnetic transition by introduction of interstitial hydrogen or partial substitution on the La or Fe sites. There is a large amount of literature on the properties and mechanism of the magnetocaloric effect in this material system, and more recently our group and several other groups have discussed the origins of the dynamics of the metamagnetic transition and its relation to magnetic hysteresis. Nevertheless, although extremely informative in other systems, there has been little spatially resolved information concerning the nature of the magnetic transition in this system. Here we use scanning Hall probe imaging to study LaFe13-xSix polycrystalline samples with x=1.2 prepared by induction melting to resolved the local static and dynamic magnetic properties. We find that the local properties of the magnetic transition are governed by chemical inhomogeneity rather that demagnetization effects associated with sample geometry.