NiMnGe is investigated by meam of X-ray diffraction, neutron diffraction, and magnetometric methods. The orthorhombic distorsion of hexagonal lattice is observed below 470 K. The compound NiMnGe is antiferromagnetic with a NBel temperature T N = 346 K.The jump observed a t temperature Tt = 186 K on the temperature dependence of magnetic susceptibility points a t the change of a magnetic structure. From the analysis of the neutron diffraction patterns .the following models of spiral magnetic structure are obtained: a t T < Tt the spiral axis is in the bc-plane. The angle between the spiral axis and the b-axis is 45", magnetic moment a t 80 K is 2 . 7 5~~; at T, < T < T N the spiral axis is along the a-axis. !The magnetic moment a t 295 K is 2 . 2 ,~~.

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Magnetic and crystallographic nature of the compounds NiMnGe1−nSin (0 ≦ n ≦ 1) are studied in the temperature range from 80 to 1000 K by X‐ray and neutron diffraction, magnetometric and DTA measurements. On the basis of these experimental data, crystallographic and magnetic phase diagram are constructed. The compounds have NiTiSi type structure at low temperatures and they transform into the Ni2In type structure at high temperatures. Magnetic and neutron diffraction measurement revealed the existence of three regions of different types of magnetic orderings: helicoidal (0 ≦ n ≦ 0.25), noncollinear (0.3 ≦ n ≦ 0.55), and ferromagnetic (0.6 ≦ n ≦ 1.0). The transition from antiferromagnetic to ferromagnetic phase implies the decrease of the MnMn distances.

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The magnetic and crystallographic nature of the compounds NiMn1−tTitGe (0 ≦ t ≦ 1) are studied by X‐ray and neutron diffraction and magnetometric measurements. It is shown that the solid solutions arise for 0 ≦ t ≦ 1, with the crystal structure of the NiTiSi type. A magnetic phase diagram is constructed: for 0 ≦ t ≦ 0.1 helicoidal order exists, for 0.15 ≦ t ≦ 0.65 a noncolinear one. NiTiGe is Pauli paramagnetic. The interpretation of the results is performed in terms of a model proposed by Jaccarino and Walker.