Magnetic structure and crystal field excitations of NdOs2Al10: a neutron scattering study.

We have investigated the magnetic properties of a polycrystalline sample of NdOs2Al10using neutron diffraction and inelastic neutron scattering, magnetic susceptibility and heat capacity measurements. The magnetic susceptibility data reveal an antiferromagnetic transition atTN1= 2.2 K while the heat capacity data which extend to lower temperatures show a further transition atTN2= 1.1 K. The INS measurements detect four well-resolved crystal field excitations at 7.4, 12.4, 17.6 meV and 19.2 meV at 5 K. The positions and intensities of the observed CEF excitations and the temperature dependence of previously published single crystal susceptibility data are analysed based on the orthorhombic CEF model of theJ= 9/2 ground state multiplet of Nd3+ion. The neutron diffraction study reveals the magnetic structure atT= 1.6 K to be of sine wave type (κ= [0, 0.723, 0]) with an ordered state moment ofμNd3+= 1.59(1)μBaligned along thea-axis in agreement with the single ion crystal field anisotropy. This indicates that the magnetism of NdOs2Al10is governed by the RKKY interactions in agreement with otherRT2Al10(R= Nd, Sm, Tb,T= Fe, Ru and Os), but different to that ofR= Ce based compounds where anisotropic two ions interaction as well as Kondo interaction govern the anomalous direction of the ordered state moment.