Evolution of magnetic and structural phase transitions in solid solutions Ni2MnGa1-xGex

ABSTRACT Structural and magnetic properties of the prominent magnetic shape memory alloy Ni2MnGa have been investigated in detail, as well as their evolution with tuning parameters – most frequently stoichiometry changes in the Ni-Mn-Ga system or substitution of one or more elements in the parent alloy by other d- and/or p-electron elements. Surprisingly, Ga-Ge substitution, although one of the most natural substitutions, has largely been neglected. We present our study on the preparation, phase and structural characterization, and magnetization properties of alloys within the Ni2MnGa1-xGex series. The isostructural substitution of Ga by Ge results in (i) a significant decrease of the melting point of the alloy, (ii) a contraction of the L21 crystal lattice following the Vegard’s law, (iii) a suppression of martensitic transformation of the lattice for x ≥ 0.25, and (iv) a substantial decrease of ferromagnetic Curie temperature with Ge content increasing above x = 0.4. Tentative signs of a possible martensitic transition are observed also for the other parent compound Ni2MnGe. The crucial role of sample annealing on its overall properties is demonstrated. The presented data are discussed in the frame of previous results on the parent alloy and other related doped systems.