Magnetoelastic coupling and magnetic phase transition in ThMn12-type TbFe11.35Nb0.65

The structural and magnetic properties of TbFe 11.35 Nb 0.65 compound were systematically investigated via high resolution synchrotron x-ray diffraction and magnetic measurements. The temperature dependence of the lattice parameters exhibits abnormal phenomena around the spin reorientation temperature T sr = 415(5) K and Curie temperature T C = 583(5) K. The variations of Wigner-Seitz cell (WSC) volume, the bond lengths between each site (2a, 8i, 8j and 8f) and the adjacent Fe atoms as well as the atomic coordinates with changing temperature demonstrate the existence of magnetoelastic coupling. Below T C , there exists large spontaneous magnetostriction in both the a and c directions. The spontaneous volume magnetostriction ω s at 100 K is derived to be ω s = 9.94 × 10 −3 . Detailed analyses of the critical magnetic behaviour around T C show that the critical exponents β, γ and δ are consistent with the values of the mean-field model, indicating that long-range interactions are dominant. Spectral fitting the Mössbauer spectrum indicates that the Nb atoms exclusively occupy the 8i site with the hyperfine interaction parameters determined for the 8i, 8j and 8f sites.