Influence of Ti atoms on the magnetic order in quaternary NiMnGe:Ti compounds

ABSTRACTThe NiMn0.95Ti0.05MnGe and Ni1–xTixMnGe (x = 0.05, 0.15 and 0.25) compounds have been studied by X-ray (at room temperature), neutron diffraction (2–360 K), DSC (130–390 K) and magnetic studies (2–350 K). The compounds with a low Ti concentration exhibit an orthorhombic crystal structure of NiTiSi-type (space group Pnma), whereas those with a large Ti content exhibit a hexagonal Ni2In-type structure (space group P63/mmc). The compounds with x = 0.05 are antiferromagnets with the helicoidal magnetic structure. The samples with the hexagonal crystal structure have a noncollinear magnetic structure with antiferro- along a-axis and ferro- along c-axis components. The obtained magnetic entropy change(ΔSMmax) has the maximum value equal to 6.2 J/kgK at T = 200 K and H = 90 kOe for Ni0.85Ti0.15MnGe. For compounds with x = 0.05, 0.15 and 0.25, the magnetic (P, T) phase diagrams, under hydrostatic pressure up to 12 kbar, were determined.