NQR andT1studies of the high-pressure phase inYbInCu4

Abstract

The pressure and temperature phase diagram of $\mathrm{Yb}\mathrm{In}{\mathrm{Cu}}_{4}$ has been investigated by nuclear quadrupolar resonance (NQR) and spin-lattice relaxation rate $({T}_{1}^{\ensuremath{-}1})$ experiments. The pressure dependence of the $^{63}\mathrm{Cu}$ NQR frequency indicates that the first-order valence transition temperature, ${T}_{v}$, does not vanish continuously at the critical pressure $({P}_{c}\ensuremath{\approx}23.7\phantom{\rule{0.3em}{0ex}}\mathrm{kbar})$ and thus there is no quantum critical point $({T}_{v}=0)$ in $\mathrm{Yb}\mathrm{In}{\mathrm{Cu}}_{4}$. This result is consistent with the ${T}_{1}^{\ensuremath{-}1}$ data, which show no evidence for non-Fermi-liquid behavior near ${P}_{c}$. For pressures $P\ensuremath{\gtrsim}{P}_{c}$, ${T}_{1}^{\ensuremath{-}1}$ increases sharply near $2.4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, which suggests the presence of critical fluctuations associated with ferromagnetic (FM) ordering. We analyze the ${T}_{1}^{\ensuremath{-}1}$, resistivity, and the pressure-enhanced susceptibility data in the mixed-valent state of $\mathrm{Yb}\mathrm{In}{\mathrm{Cu}}_{4}$ and find no evidence to indicate that the pressure-induced FM phase can be described by the Stoner theory for itinerant ferromagnetism. Rather, the pressure-induced FM order may be due to pressure-stabilized ${\mathrm{Yb}}^{3+}$ local moments. We also examine the possibility of FM order induced by an external magnetic field near ${P}_{c}$, but find no evidence down to $1.5\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.