Probing glassiness in Heuslers via density functional theory calculations

Heusler compounds and alloys form a unique class of intermetallic systems with functional properties interfering with basic questions of fundamental aspects of materials science. Among the functional properties, the magnetic shape memory behavior (Planes et al., J Phys: Condens Matter 21:233201 (29 pp), 2009) and the ferrocaloric effects like the inverse magnetocaloric effect which is associated with the first order magnetostructural transformation with a jump-like change of the magnetization with lowering of temperature (Acet et al., Magnetic-field-induced effects in martensitic Heusler-based magnetic shape memory alloys. In: Bushow KHJ (ed) Handbook of magnetic materials, vol 19. North-Holland, Amsterdam, pp 231–289, 2011) have been intensively investigated in various reviews. Important references can be found in Acet et al. (Magnetic-field-induced effects in martensitc Heusler-based magnetic shape memory alloys. In: Bushow KHJ (ed) Handbook of magnetic materials, vol 19. North-Holland, Amsterdam, pp 231–289, 2011). Besides magnetocaloric effects, other ferroic cooling mechanisms of Heuslers (electrocaloric, barocaloric, and elastocaloric ones) have recently been discussed by Xavier Moya et al. (Nat Mater 13:439–450, 2014). A discussion of caloric effects in ferroic materials including a brief discussion of the importance of correlating time and length scales can be found in Fähler et al. (Adv Eng Mater 14:10–19, 2012). In the present article, we emphasize this item further by showing that, in particular, the physics at different time scales leads to markedly different properties of the Heusler materials. “Rapidly quenched” alloys behave differently from “less rapidly quenched” alloys. In the latter case, the so-called magnetostructural transformation may vanish altogether because of segregation of the alloys into the stoichiometric L2₁ Heusler phase and L1₀ Ni-Mn occurs. We argue that this tendency for segregation is at the origin of glassiness in Heuslers.