Unconventional $T-H$ Phase Diagram in the Noncentrosymmetric Compound ${\mathrm{Yb}}_2{\mathrm{Fe}}_{12}{\mathbf{P}}_7$

The temperature–($T$-)magnetic-field ($H$) phase diagram for the noncentrosymmetric compound ${\mathrm{Yb}}_2{\mathrm{Fe}}_{12}{\mathrm{P}}_7$, determined from electrical resistivity ($\rho$), specific heat ($C$), and magnetization ($M$) measurements on single crystal specimens, is reported. This system exhibits a crossover from a magnetically ordered non-Fermi-liquid (NFL) phase at low $H$ to another NFL phase at higher $H$. The crossover occurs near the value of $H$ where the magnetic ordering temperature ($T_M$) is no longer observable in $C(T,H)/T$ and $\rho (T,H)$, but not where $T_M$ extrapolates smoothly to $T=0\mathrm{K}$ at a possible quantum critical point (QCP). This indicates the occurrence of a quantum phase transition between the two NFL phases. The lack of a clear relationship between the extrapolated QCP and NFL behavior suggests an unconventional route to the NFL ground states.

Figure 1

(a) Magnetic susceptibility $\chi =M/H$ vs temperature $T$ for magnetic field $H$ applied perpendicular and parallel to the $c$ axis. The solid lines are the CW fits to the data (see text). (b) $M$ vs $H$ for $H\parallel c$. (c) $M$ vs $H$ for $H\perp c$.

Figure 2

(a) Derivative of the electrical resistivity with respect to temperature, $\partial \rho (T,H)/\partial T$. (b) Expanded view of specific heat divided by temperature $C_p(T,H)/T$ for $T<2\mathrm{K}$ and $H<1\mathrm{T}$. (c) Electronic portion of the entropy $S_e(T,H=0)$ for $T<5\mathrm{K}$. (d) $C_p/T$ vs $T$ for several $H$.

Figure 3

(a) Electrical resistivity $\rho$ vs temperature $T$ for 0.05–1 K and magnetic fields $H\perp c$ axis. (b) $\rho -{\rho }_0$ vs $T$ on a log-log plot. Fits are described in the text. (c) $\rho$ vs $T$ for $T=0.05–290\mathrm{K}$ and $H=0\mathrm{T}$. (d) $\rho$ vs $T$ for $T=0.05–5\mathrm{K}$ and $H=0\mathrm{T}$.

Figure 4

(a)–(c) Magnetic field $H$ dependence of the quantities ${\rho }_0$, $A$, and $n$ from power law fits to the electrical resistivity data $\rho (T)$ (see text). (d) $T-H$ phase diagram for ${\mathrm{Yb}}_2{\mathrm{Fe}}_{12}{\mathrm{P}}_7$. The values for $T_M$ are taken from measurements of $C_p(T,H)$ (triangles) and $\rho (T,H)$ (upside-down triangles). The dashed line is an extrapolation of $T_M$ to 0 K. The color gradient represents $\partial \ln (\rho -{\rho }_0)/\partial \ln T$, where ${\rho }_0$ maximizes the $T$ range for the low $T$ power law behavior for each $\rho (T,H)$. The values of $\partial \ln (\rho -{\rho }_0)/\partial \ln T$ above the low $T$ fit range do not represent the local exponent $n$ since they are based on ${\rho }_0$ values from the low $T$ fits. Note that the low $T$ power law fit range appears to be reduced from what would be inferred from Fig. 3b. This is because the data are smoothed before taking $\partial \ln (\rho -{\rho }_0)/\partial \ln T$, resulting in a reduction of the apparent fit range because adjacent averaging samples the lower slope data above the upper $T$ limit of the fit range.