A Neutron Diffraction Investigation of the Magnetic Structure of TbMn2

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Abstract
TbMn2 crystallizes with the cubic Laves‐phase structure (C15‐type) which may be regarded as the spinel structure without the anions. The ``A'' sites are occupied by Tb ions and the ``B'' sites by Mn ions. Neutron diffraction powder patterns run at 4.2°K exhibit a number of extra reflections characteristic of a modulated magnetic structure. These additional reflections can be indexed on the basis of a spiral modulation propagated along [110] with a wavelength of 8.0 Å. The spiral axis is along [001]. The ``B'' sites are ordered in a manner which is entirely analogous to the low‐temperature ordering of Fe3O4; the two sublattice spirals being 180° out of phase. The A sublattice is in phase with a particular one of the two B sublattices. The combination of the internally compensated B sites and the ferromagnetically coupled A sites leads to a ferrimagnetic spiral.