Pressure-Induced Valence Crossover and Novel Metamagnetic Behavior near the Antiferromagnetic Quantum Phase Transition of ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$

We report electrical resistivity, ac magnetic susceptibility, and x-ray absorption spectroscopy measurements of intermediate valence ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$ under pressure and magnetic field. We have revealed a characteristic pressure-induced Yb valence crossover within the temperature-pressure phase diagram, and a first-order metamagnetic transition is found below $P_c\sim 9\mathrm{GPa}$ where the system undergoes a pressure-induced antiferromagnetic transition. As a possible origin of the metamagnetic behavior, a critical valence fluctuation emerging near the critical point of the first-order valence transition is discussed on the basis of the temperature-field-pressure phase diagram.

Figure 1

(a) Temperature dependence of ${\rho }_{\text{mag}}$ of ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$ under various pressures. The inset shows $T$ dependence of ${\chi }_{\text{ac}}^{\prime }$ at various pressures. The distinct anomalies as marked by arrows at $T_N$ in ${\rho }_{\text{mag}}$ and ${\chi }_{\text{ac}}^{\prime }$ correspond to the AFM transition. (b) ${\rho }_{\text{mag}}$ as a function of $T^2$ at selected pressure. The inset shows the low-temperature ${\rho }_{\text{mag}}$ at 9.0 GPa in a linear scale. (c) The log-log plot of $A$ coefficient and $T_{\max }$. The broken line indicates $A\propto T_{\max }^{-2}$.

Figure 2

(a) XAS spectra of ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$ at selected pressures and temperatures for the Yb $L_3$ edge. (b) Temperature dependence of the averaged valence for various pressures.

Figure 3

Magnetic field and temperature dependence of ${\chi }_{\text{ac}}^{\prime }$ in ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$ at (a),(b) 8.5 GPa and (c),(d) 9.5 GPa. Curves are shifted for clarity. The upper insets in (a) and (c) are hysteresis curves of ${\chi }_{\text{ac}}^{\prime }(H)$ measurements at $T=0.4\mathrm{K}$.

Figure 4

Contour plot of the Yb valence in the temperature-pressure phase diagram of ${\mathrm{YbNi}}_3{\mathrm{Ga}}_9$. The transition and crossover temperatures are deduced from resistivity (circles) and ac magnetic susceptibility (squares) measurements. Here, closed squares below and above $P_c$ indicate the CP and TCP, respectively. The dashed lines are guides to the eye.