Thermal hysteresis is recognized as one of the main drawbacks for cyclical applications of magnetocaloric and ferromagnetic shape memory materials with first-order transformations. As such, the challenge is to develop strategies that improve the compatibility between the phases involved in the transitions and study its influence on thermal hysteresis. With this purpose, we explore the thermal, structural, and magnetic properties of the Ni2Mn1-xCuxGa0.84Al0.16 Heusler alloys. The alloys present a thermal hysteresis reduction of ∼60% when the Cu content in the compound varies from x=0.10 to x=0.25, with a minimum hysteresis width of 6 K being achieved. We applied the geometric nonlinear theory of martensite to address the phase compatibility, quantified by the parameter λ2, the middle eigenvalue of the transformation stretch tensor, and found that the minimum of hysteresis is associated with a better crystallographic compatibility (λ2 closer to 1) between the austenite and martensite phases. In addition, we show that the valleylike properties of hysteresis found in the Ni2Mn1-xCuxGa0.84Al0.16 compounds is present in several other alloys in the literature. These results provide pathways to understand as well as to master the phase compatibility and ultimately achieve a low thermal hysteresis in multifunctional Heusler alloys.
Bibliographical noteFunding Information:
A.A.M. was supported by a graduate grant from the Brazilian agency CAPES (Coordenação de Aperfeiçoamento de Pessoal de Nível Superior). L.G. and A.M.G. were supported by CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) Projects No. 305021/2017-6 and No. 424688/2018-2. L.G. acknowledges financial support from FAPERJ (Fundação Carlos Chagas Filho de Amparo a Pesquisa do Estado do Rio de Janeiro), Projects No. E-26/202.820/2018 and No. E-26/010.101136/2018. H.G. and R.D.J. acknowledge the support of NSF (Grant No. DMREF-1629026), ONR (Grant No. N00014-18-1-2766), and a Vannevar Bush Faculty Fellowship. L.F.C was supported by UK EPSRC Project No. EP/P511109/1 and Innovate UK FlexMag Project No. 105541 or 32645.
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