Annealing-tuned Hall coefficient in single crystals of the YbNi${}_2$B${}_2$C heavy fermion

Abstract

We present temperature-dependent magneto-transport measurements on as-grown and annealed YbNi${}_2$B${}_2$C single crystals. Annealing causes drastic changes in the Hall coefficient, $R_H(T)$. Whereas for as-grown samples the Hall coefficient is negative between room temperature and 2 K, with a pronounced {\it minimum} at $\approx 22$ K, for the samples annealed at $950^{\circ }$ C for 150 hours, $R_H(T)$ changes its sign twice in the same temperature range: from negative to positive on cooling below $\sim 100$ K and back to negative below $\sim 10$ K, and has a clear {\it maximum} at $\approx 45$ 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 YbNi${}_2$B${}_2$C.