Abstract
Off stoichiometric Heuslers in the form Ni50Mn50−xZx, where Z can be a group 13–15 element of the periodic system, decompose at about 650 K into a ferromagnetic full Heusler Ni50Mn25Z25 and an antiferromagnetic Ni50Mn50 component. We study here the case for Z as Sb and report on shell-ferromagnetic properties as well as thermal instabilities. Unlike the case for other Z-elements, in Ni50Mn50−xSbx, the minimum decomposition temperature corresponds to a temperature lying within the austenite state so that it is possible to observe the change in the martensitic transition temperature while annealing, thus providing further information on the change of composition during annealing. Scherrer analysis performed on emerging peaks related to the cubic full-Heusler shows that the precipitate size for shell-FM properties to become observable is around 5-10 nm. Other than vertical shifts in the field-dependence of the magnetization, which are also observed in compounds with Z other than Sb, concurrent exchange-bias effects are observed in the case with Z as Sb.
Highlights
Heusler alloys have many functionalities based on the presence of first order magnetostructural transitions
Unlike the case for other Z-elements, in Ni50Mn50ÀxSbx, the minimum decomposition temperature corresponds to a temperature lying within the austenite state so that it is possible to observe the change in the martensitic transition temperature while annealing, providing further information on the change of composition during annealing
What is distinct about Ni50Mn45Sb5 is that the decomposition temperature of 650 K lies within the austenite state and not within the martensite state as for the other Z-elements
Summary
Heusler alloys have many functionalities based on the presence of first order magnetostructural transitions. These appear in Ni-Mn-based Heuslers with composition Ni50Mn50ÀxZx where Z can be Al, Ga, In, Sn, and Sb.[1] They have potential room-temperature applications in the areas of magnetic shape-memory,[2,3] magnetocalorics,[4,5] and giant magnetoresistance.[6] These alloys are interesting for their functionalities, but they serve as prototypes for investigating basic physical phenomena such as solid-solid phase transitions,[7] kinetic arrest,[8,9] and intrinsic exchange bias,[10–12] most of which are related to the presence of mixed magnetic interactions at the microscopic scale Just how these interactions relate to the multifunctional properties in the macroscopic scale is a topic of current research.
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