Spin-reorientation in quaternary Dy_2Fe_2Si_2C

Abstract

The low temperature magnetic properties of Dy_2Fe_2Si_2C have been investigated by magnetisation, specific heat, neutron powder diffraction and "5"7Fe Mössbauer spectroscopy measurements. In contrast to other R_2Fe_2Si_2C compounds, we found that Dy_2Fe_2Si_2C undergoes two successive magnetic transitions at low temperatures. The first magnetic transition at T_N = 26(2) K is associated with the transition from paramagnetic to antiferromagnetic states, whereas our neutron diffraction and "5"7Fe Mössbauer spectroscopy studies reveal that the second magnetic transition at T_t = 6(2) K is likely related to a spin-reorientation of the Dy moments rather than the independent ordering of the Fe sublattice. The magnetic structure above T_t can be described with a propagation vector k = [0 0 1/2] with the ordering of the Dy magnetic moments along the monoclinic b-axis, whereas on cooling below T_t the Dy moment tips away from the b-axis towards the ac-plane. Magnetocrystalline anisotropy energy calculations show that a canted magnetic structure is more energetically favourable below T_t than b-axis order due to the important influence of higher-order crystal field terms at low temperatures, thus explaining the unique occurrence of spin reorientation in Dy_2Fe_2Si_2C compared with other R_2Fe_2Si_2C compounds.