Dynamics of the phase transformation in a giant magnetocaloric material along T- and B-scans

• Thermal model describing first-order transition on Peltier DSC under both T and B scans. • Experimental validation of the model (latent heat, relaxation times, thermal parameters) • Nontrivial relation between the instantaneous transformation rate and the heat flux. • Influence of the nature, direction, and sweeping rate of the driving parameter. All giant magnetocaloric materials exhibit an extreme first-order character which makes them particularly suitable to investigate the peculiarities associated to this type of transition. In the present study, we explored the time dependence of the heat exchanges, from or towards a LaFeSiCo alloy, by using a home-made differential scanning calorimeter based on Peltier cells. A thermal modelling of the experimental set-up was developed to analyse the various regimes present before, along, and after the transformation. This model allows to recover the expected values of latent heat and it predicts relaxation times consistent with the data up to certain limits in rate (about 0.5 K/min and 150 Oe/s). The heart of our study was focused on the transitional regime for which we derived the instantaneous rate of transformation (taking the form of a succession of spikes). We explored in detail the impacts of the nature of the driving parameter (temperature or field), the direction of crossing the transition, the scanning rate and the thermal coupling of the sample.