Avoided Antiferromagnetic Order and Quantum Critical Point in $\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}{\mathrm{n}}_{\mathrm{5}}$

We measured the specific heat and resistivity of heavy fermion $\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}{\mathrm{n}}_{\mathrm{5}}$ between the superconducting critical field $H_{c2}=5\mathrm{T}$ and 9 T, with the field in the [001] direction, and at temperatures down to 50 mK. At 5 T the data show a non-Fermi liquid (NFL) behavior down to the lowest temperatures. At the field above 8 T the data exhibit a crossover from the Fermi liquid to a non-Fermi liquid behavior. We analyzed the scaling properties of the specific heat and compared both the resistivity and the specific heat with the predictions of a spin-fluctuation theory. Our analysis leads us to suggest that the NFL behavior is due to incipient antiferromagnetism (AFM) in $\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}{\mathrm{n}}_{\mathrm{5}}$ with the quantum critical point in the vicinity of $H_{c2}$. Below $H_{c2}$ the AFM phase which competes with the paramagnetic ground state is superseded by the superconducting transition.

Figure 1

(a) Sommerfeld coefficient, $\gamma (T)=C(T)/T$, of ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$ in magnetic fields $H\parallel [001]$. Dashed lines for 8 and 9 T emphasize the FL behavior with constant $\gamma$. Left (right) arrows indicate $T_{\mathrm{F}\mathrm{L}}^C$ for 8 T (9 T). Solid lines are fits to the SCR spin-fluctuation model for each field with the corresponding values of $y_0$; see text for details. (b) Scaling analysis of the data in (a) for $\alpha =0.71$ and $\beta =2.5$. Inset: For different values of $\beta$ we plot values of $\alpha$ which minimize ${\chi }^2$ for a given $\beta$, and ${\chi }^2$ for these $\alpha$ and $\beta$.

Figure 2

(a) Resistivity of ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$ in magnetic field $H\parallel [001]$ above the critical field $H_{c2}=4.95\mathrm{T}$. Inset: Fits to $\Delta \rho (T)$ below 2 K from the spin-fluctuation theory as detailed in the text. Solid lines: $y_0=0.14$, 0.33, 0.5, and 0.8 from top to bottom. (b) Low temperature region of data in (a). Inset (d) ${\gamma }^2$ vs $A$. The solid line is a linear fit to the data points and the origin. Inset (c) Resistance for 6 and 9 T plotted vs $T^2$. All symbols are as indicated in (a).

Figure 3

Combined phase diagram of ${\mathrm{C}\mathrm{e}\mathrm{C}\mathrm{o}\mathrm{I}\mathrm{n}}_5$. Superconducting-normal phase boundary [(○) and solid line] is from Ref. 16. $T_{\mathrm{c}\mathrm{r}}$ (□) and the dashed line (guide to the eye) denote the upper boundary of the crossover region. Dotted lines through $T_{\mathrm{F}\mathrm{L}}^C$ (◇) and $T_{\mathrm{F}\mathrm{L}}^{\rho }$ (△) schematically indicate the upper boundary of the FL region. The region between the dashed and the dotted lines is the crossover region.