The development of new ferromagnetic shape memory alloys in Ni-Mn-Ga system

Abstract

The Ferromagnetic Heusler alloy Ni$AnGa is known to undergo a structural phase transformation of marten&c type. Thermoelastic nature, shape memory effect @ME) and superelasticity were found in (1) to be intrinsic to this transformation. Hence the martensitic transformation (MT) in NiwGa appeared to be a subject of further intensive investigations last few years. It tumcd out that the Ni&lnGa alloy was an affluent object to search ftx new phenomena such as magnetoelastic behavior in the vicinity of MT (2) and martensite lattice softening while approaching the intermartensitic transformation temperature during heating (3). In fact all the data published before were obtained using two Ni&lnGa samples of near stoichiometric composition. Despite the small composition difference the two mentioned Ni&lnGa alloys (alloys 3 and 10 in Table 1) studid e.g. in (Z!, 3), possess entirely Werent martensitic temperatures, Iv&. So, the high sensitivity of M. to the deviation ILi-om the stoichiometric composition can be drawn as an important conclusion. In this work we present the results of the investigation of the following problems: how M,, the thermal hysteresis, Curie temperature, transformation heat are a&&d by the composition variation in the Ni-Mn-Ga alloy system in a concentration interval for each component of about 10 at. %. This work was performed to make sure that lhe new family of Ni-Mn-Ga based shape memory alloys @MA) with a wide variety of structural and magnetic properties is actually elaborated.