Structural and magnetic properties of Ni₂In type (Mn_1-xNi_x)₆₅Ga₃₅ compounds

New intermetallic compounds (Mn_1-xNi_x)₆₅Ga₃₅ of Ni₂In type structure are found in the range of 0.15≤x≤0.45. In the higher x range, the magnetization-temperature curves show Curie-Weiss type behaviors, but those with x≤0.35 suggest another type ferromagnet. The magnetic ordering temperature T_c decreases for x≤0.2 and then increases with increasing x. The curves of 0.25≤x≤0.3 show a hump and then slightly decrease with decreasing temperature. In the neutron diffraction experiment for x = 0.275. the (0 0 1) reflection appears for 165 K≤T≤218 K indicating the presence of an antiferromagnetic component lying in basal plane. For T≤165 K, the satellite lines of (0 0 1) suggest an appearance of incommensurate phase, perhaps of a helical spin structure, changing the pitch of helix from 5.78C to 8.47C with temperature.