Capturing first- and second-order behavior in magnetocaloricCoMnSi0.92Ge0.08

Here we examine the constituent components that make a magnetocaloric material attractive for application. The field-temperature phase diagram is studied and using calorimetry, the 1 and 2 order components of the magnetic field driven magneto-structural phase transition in CoMnSi0.92Ge0.08 are extracted. It is demonstrated that below 262K the transition shows a latent heat component associated with first order behavior when the material changes from antiferromagnetic to ferromagnetic order. Such a transition is known as a metamagnetic transition. We identify 262K as a tricritical point and above this temperature Tcrit the transition shows only continuous, 2 order characteristics. Hall probe imaging that has a five micron pixel resolution is then used to study the striking differences in the spatial evolution of the transition above and below Tcrit. We demonstrate that the hysteresis of the transition is linearly related to the magnitude of the latent heat; an observation that has important implications for the use of this and other 1 order systems for application as magnetic refrigerants.