Tuning the Hall coefficient in single crystals of the heavy fermion compound ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ by annealing

We present temperature-dependent magnetotransport measurements on as-grown and annealed ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ single crystals. Annealing causes drastic changes in the Hall coefficient, $R_H\left(T\right)$. Whereas for as-grown samples the Hall coefficient is negative between room temperature and 2 K, with a pronounced minimum at $\approx 22\mathrm{K}$, for the samples annealed at 950 °C for 150 h, $R_H\left(T\right)$ changes its sign twice in the same temperature range: from negative to positive on cooling below $\sim 100\mathrm{K}$ and back to negative below $\sim 10\mathrm{K}$, and has a clear maximum at $\approx 45\mathrm{K}$. Intermediate temperature dependencies can be achieved by reducing the annealing time. These findings are discussed within the framework of an annealing dependence of the skew scattering in conjunction with the recent structural, thermodynamic and transport studies of the effects of annealing in ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$.

Figure 1

(a) Zero-field resistivity of as-grown ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ (line) and ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$ (line) and annealed at 950 °C for 150 h ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ (엯) and ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$ (▵) samples. Inset: sketch of the contact arrangement for simultaneous resistivity and Hall effect measurements (subscripts $R$ and $H$, respectively, in the sketch). (b) Zero-field resistivity of four as-grown ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ crystals (lines), and the same samples annealed at 950 °C for 150 (엯), 48 (▵), 20 (▾), and 5 (◇) h.

Figure 2

Field-dependent Hall resistivity measured at different temperatures for (a) as-grown ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$; (b) annealed ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$, and (c) annealed ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$. Annealing conditions are shown on the respective panels; symbols are consistent for all four panels.

Figure 3

The temperature-dependent Hall coefficient measured at $H=90\mathrm{kOe}$ for as-grown ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ (line) and ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$ (line) and annealed at 950 °C for 150 h ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ (엯) and ${\mathrm{LuNi}}_2{\mathrm{B}}_2\mathrm{C}$ (▵) samples.

Figure 4

Temperature-dependent (a) Hall coefficient measured at $H=90\mathrm{kOe}$ and (b) the product of magnetic susceptibility and resonant scattering part of the resistivity, $\chi \left(T\right)[{\rho }_{\mathrm{Yb}}\left(T\right)-{\rho }_{\mathrm{Lu}}\left(T\right)]$ for as-grown (lines) and annealed at 950 °C for 150 h (엯) ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ crystals. Dotted and dashed lines mark positions of the extrema in the curves for as-grown and annealed samples, respectively.

Figure 5

Temperature-dependent (a) Hall coefficient measured at $H=90\mathrm{kOe}$ and (b) product of magnetic susceptibility and resonant scattering part of resistivity, $\chi \left(T\right)[{\rho }_{\mathrm{Yb}}\left(T\right)-{\rho }_{\mathrm{Lu}}\left(T\right)]$ for as-grown (lines) and annealed at 950 °C for 150 (엯), 48 (▵), 20 (▾), and 5 (◇) h ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ crystals. Note: data in (b) are plotted as $-\chi \left(T\right){\rho }_{\mathit{magn}}\left(T\right)$ for easier comparison with ${\rho }_H∕H$ data in (a).