First-Order Magnetostructural Phase Transition in AlFe$_{2}$B$_{2}$

Understanding correlations between composition and crystal structure is key to tailoring the response of functional magnetic materials. In particular, the ferromagnetic AlFe$_2$B$_2$ compound with the layered AlMn$_2$B$_2$-type structure is reported to exhibit a magnetic transition of relevance for magnetocaloric cooling, with a reported entropy change $\Delta S \sim$ 4J/kg-K at an applied magnetic field of 2 T1.\footnote{X. Tan et al., J. Am. Chem. Soc., 135(2012) 9553.} New results derived from magnetic, structural and calorimetric probes confirm a thermodynamically first-order magnetic phase change in AlFe$_2$B$_2$ in the vicinity of the Curie temperature of $\sim$300 K. The transformation from the ferromagnetic to the paramagnetic state is accompanied by a non-uniform 1\% unit cell volume expansion upon heating, signifying that application of magnetic field is anticipated to have a similar effect (stabilizing the ferromagnetic phase) as the application of chemical or hydrostatic pressure. Relevant barocaloric effects are expected in this compound.