Magnetic structure and preferential occupation of Fe in the composite compound Nd2Co6Fe

Abstract: The crystal and magnetic structures of the composite compound Nd2Co6Fe have been investigated by high-resolution neutron powder diffraction and X-ray powder diffraction. The compound crystallizes in the hexagonal Ce2Ni7-type structure consisting of Nd(Co,Fe)2 and Nd(Co,Fe)5 structural blocks alternately stacked along the c-axis. Multi-pattern Rietveld refinement of neutron diffraction and X-ray diffraction data at room temperature reveal that substitution of Fe for Co occurs exclusively in the Nd(Co,Fe)5 structural blocks. The preferential occupation of the Fe atoms in the structure is discussed based on the mixing enthalpy between Nd and Fe atoms and on the lattice distortions. In agreement with the reported magnetic phase diagram of the Nd2Co7−x Fe x compounds, magnetic structure models with the moments of all atoms in the ab plane at 300K and along the c-axis at 450K provide a satisfactory fitting to the experimental neutron diffraction data. The refinement results show that the atomic moments of (Co,Fe) atoms within the Nd(Co,Fe)5 blocks decrease slightly with temperature, whereas the atomic moments of Nd in the compound and of (Co,Fe) atoms at the interface between the Nd(Co,Fe)2 and Nd(Co,Fe)5 blocks are reduced significantly. [Copyright &y& Elsevier]