Heterogeneous nucleation and heat flux avalanches in La(Fe, Si)13 magnetocaloric compounds near the critical point

The phase transformation kinetics of LaFe11.41Mn0.30Si1.29-H1.65 magnetocaloric compound is addressed by low ratecalorimetry experiments. Scans at 1 mK/s show that its first order phase transitions are made by multiple heat fluxavalanches. Getting very close to thecritical point, when thetransition becomes of the second order type, the step-like discontinuous behaviour associated withavalanches is smoothed out and the thermalhysteresis disappears. This result is confirmed by magneto-resistivitymeasurements and allows to obtain accurate values of the temperaturehysteresis ( ΔThyst = 0.37 K) at zero externalmagnetic field and of the critical field (Hc = 1.19 T). The number and magnitude of heat fluxavalanches change as themagnetic field strength is increased, showing the interplay between the intrinsic energy barrier between phases and the microstructural disorder of the sample.

Source: Applied Physics Letters - December 5, 2016 Category: Physics Authors: C. Bennati, L. Gozzelino, E. S. Olivetti and V. Basso Source Type: research