Shell-ferromagnetism and decomposition in off-stoichiometric Ni50Mn50–xSbx Heuslers

Off stoichiometric Heuslers in the form Ni 50Mn 50 − x Z x, where Z can be a group 13–15 element of the periodic system, decompose at about 650 K into a ferromagnetic full Heusler Ni 50Mn 25 Z 25 and an antiferromagnetic Ni 50Mn 50 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 Ni 50Mn 50 − xSb x, 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, concurre...