Investigation of the Magnetic Structure of ErMn2, TmMn2, TbNi2 by Neutron Diffraction

Magnetic measurements by H. J. Williams (ErMn2 and TmMn2), and W. E. Wallace (TbNi2) have shown that these compounds are magnetically ordered at low temperature with a net moment per formula unit lower than that of the free rare-earth ion. Neutron diffraction powder patterns have been used to determine the actual magnetic structure. ErMn2 and TmMn2 crystallize with the hexagonal Laves phase structure (C-14 type). ErMn2 is ferromagnetic, with a moment of 7.72 μB/Er atom at 4.2°K aligned along the c axis. No detectable moment on Mn is observed. TmMn2 is almost completely ferromagnetic, with a moment of 4.95 μB/TM atom at 2.1°K aligned along the c axis, and essentially zero moment for Mn. A faint additional line at low angle seems to indicate a weak antiferromagnetic contribution. TbNi2 crystallizes with the cubic Laves phase structure (C-15 type). At 4.2°K, ferromagnetic lines as well as additional peaks appear in the diffraction pattern, but the magnetic scattering is rather sensitive to sample preparation.