Neutron diffraction and x-ray resonant exchange-scattering studies of the zero-field magnetic structures ofTbNi2Ge2

Abstract

The zero-field magnetic structures of the rare-earth intermetallic compound ${\mathrm{TbNi}}_{2}{\mathrm{Ge}}_{2}$ have been determined using conventional magnetic neutron diffraction and high-resolution x-ray resonant exchange scattering techniques. There are two distinct magnetic phase transitions in this material: one is from the high-temperature paramagnetic state to a long period antiferromagnetic phase at the N\'eel temperature ${(T}_{N}=16.8 \mathrm{K}),$ and the other is at a lower temperature ${(T}_{t}=9.3 \mathrm{K}),$ where the system locks into a commensurate phase. The structure above ${T}_{t}$ is described by a longitudinal, amplitude modulated, sinusoidal wave with propagation vector ${\mathit{\ensuremath{\tau}}}_{1}\ensuremath{\approx}(000.758\ifmmode\pm\else\textpm\fi{}0.002)$ in reciprocal-lattice units (r.l.u.). As the temperature is lowered below ${T}_{t},$ ${\mathit{\ensuremath{\tau}}}_{1}$ locks at $(0 0 \frac{3}{4})$ and additional magnetic Bragg reflections corresponding to ${\mathit{\ensuremath{\tau}}}_{2}=(\frac{1}{2} \frac{1}{2} 0)$ and ${\mathit{\ensuremath{\tau}}}_{3}=(\frac{1}{2} \frac{1}{2} \frac{1}{2})$ develop. A weak modulation ${\mathit{\ensuremath{\tau}}}_{1}^{\ensuremath{'}}=(0 0 \frac{1}{4}),$ related to ${\mathit{\ensuremath{\tau}}}_{1}$ also appears indicating a squaring-up of the low-temperature structure. In this equal moment structure all Tb moments have the saturation value of ${\ensuremath{\mu}}_{s}=9.0\ifmmode\pm\else\textpm\fi{}0.2{\ensuremath{\mu}}_{\mathrm{B}}.$ Both the phases are uniaxial with Tb moments parallel to the $\mathbf{c}^$ axis of the tetragonal unit cell.