Magnetic ordering in TmGa

We have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and ¹⁶⁹Tm Mössbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an
incommensurate antiferromagnetic structure described by the propagation vector k₁ = [0 0.275(2) 0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches
6.7(2) μ_B at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) μ_B. The ¹⁶⁹Tm hyperfine magnetic field at 5 K is 631(1) T.