Incommensurate antiferromagnetism induced by a charge density wave in the cubic phase of ${\mathrm{TbGe}}_{2.85}$

Temperature dependencies of the electrical resistivity, magnetic susceptibility, and heat capacity have been obtained in the cubic phase of ${\mathrm{TbGe}}_{2.85}$ (the ${\mathrm{AuCu}}_3$ structure), synthesized at high pressure. The macroscopic measurements indicate that a charge density wave is formed below 145 K and an antiferromagnetic ordering is realized below 19 K. Hyperfine interaction data obtained with the time differential perturbed angular correlation method with ${}^{111}\mathrm{Cd}$ probes inserted in the ${\mathrm{TbGe}}_{2.85}$ lattice suggest that the charge density wave is incommensurate in the temperature region 19–145 K, but becomes commensurate below 19 K. The neutron diffraction reveals a complex antiferromagnetic spiral structure in the magnetically ordered phase. We discuss relations between the charge density wave and helical ordering in ${\mathrm{TbGe}}_{2.85}$ and ${\mathrm{TbPd}}_3$.

Figure 1

$\chi$ and ${\chi }^{-1}$ as a function of temperature in the range 2–300 K for ${\mathrm{TbGe}}_{2.85}$.

Figure 2

Difference between the experimental data for ${\chi }^{-1}$ and the Curie-Weiss fit (${\chi }_{\mathrm{CW}}^{-1}$) for ${\mathrm{TbGe}}_{2.85}$.

Figure 3

Resistivity of ${\mathrm{TbGe}}_3$ and ${\mathrm{TbGe}}_{2.85}$ vs temperature. The red and blue dots represent data for ${\mathrm{TbGe}}_{2.85}$ for different external pressures (see text for details), while the black dots for ${\mathrm{TbGe}}_3$.

Figure 4

Heat capacity vs temperature (blue dots) and Debyes law approximation with ${\mathrm{\Theta }}_D=205$ K (red line). (Inset) $C/T$ vs $T$.

Figure 5

TDPAC spectra of ${}^{111}\mathrm{Cd}$ probes in ${\mathrm{TbGe}}_{2.85}$ in the temperature range 30–300 K. Left panels give the angular anisotropic functions $R\left(t\right)$ and their fits, right panels represent Fourier transforms of $R\left(t\right)$ with resolved quadrupolar frequencies.

Figure 6

The quadrupole frequency ${\nu }_Q$ as a function of temperature in the range 4–50 K. The hatched interval marks the onset of antiferromagnetic-paramagnetic transition.

Figure 7

TDPAC spectra $R\left(t\right)$ of ${}^{111}\mathrm{Cd}$ probes in ${\mathrm{TbGe}}_{2.85}$ and their fits (red lines) in the temperature range 4–22 K.

Figure 8

Crystallographic structure of ${\mathrm{TbGe}}_{2.85}$ in the antiferromagnetic state with magnetically and electronically nonequivalent Ge sites. Large spheres represent Tb atoms, small spheres Ge atoms. Electronically nonequivalent Ge sites are shown by different colors, magnetically nonequivalent by different arrows.

Figure 9

Refined neutron powder diffraction pattern of ${\mathrm{TbGe}}_{2.85}$ at 300 K.

Figure 10

Refined neutron powder diffraction pattern of ${\mathrm{TbGe}}_{2.85}$ obtained at 10 K in the magnetically ordered state. (a) Data for $1<d<5$ and (b) data for $4<d<10$. The $(0,0,1)$ and $(1,0,1)$ peaks are shown in both panels for comparison of their intensities.

Figure 11

Temperature dependence of the resistivity of ${\mathrm{TbPd}}_3$.