Phase formation characteristics and magnetic properties of bulk Ni2MnGe Heusler alloy

We have systemically studied the effects of annealing temperature and alloy composition on the structural and magnetic properties of bulk Ni2MnGe and Ni2.1Mn0.9Ge Heusler alloys. We have observed that both annealing temperature and the alloy composition drastically alter the phases found in the samples due to the presence of competing ternary phases. Annealing at 900 and 950 °C for both alloy compositions facilitate the formation of L21 Heusler phase. Nevertheless, formation of Ni5Mn4Ge3 and Ni16Mn6Ge7 phases cannot be prevented for Ni2MnGe and Ni2.1Mn0.9Ge alloys, respectively. In order to estimate the magnetic contribution of the Ni5Mn4Ge3 impurity phase to that of the parent Ni2MnGe, we have also synthesized pure Ni5Mn4Ge3 alloy. Antiferromagnetic nature of Ni5Mn4Ge3 with low magnetization response allows us to reveal the magnetic response of the stoichiometric bulk Ni2MnGe. Bulk Ni2MnGe shows simple ferromagnetic behavior with a Curie temperature of 300 K, in agreement with the previous results on thin films. Despite the divergence of magnetization curves between field cooled (FC) and field heated (FH) modes, stoichiometric Ni2MnGe alloy does not undergo a martensitic phase transition based on our variable temperature X-ray diffraction experiments.