Multiple ordered phases in the filled skutterudite compound $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{As}}_{12}$

Magnetization, specific heat, and electrical resistivity measurements were made on single crystals of the filled skutterudite compound $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{As}}_{12}$. Specific heat measurements indicate an electronic specific heat coefficient $\gamma \sim 50–200\mathrm{mJ}∕\mathrm{mol}{\mathrm{K}}^2$ at temperatures $10\mathrm{K}⩽T⩽18\mathrm{K}$, and $\sim 1\mathrm{J}∕\mathrm{mol}{\mathrm{K}}^2$ for $T⩽1.6\mathrm{K}$. The combined measurements reveal the presence of two, or possibly three, ordered phases at temperatures below $\sim 2.3\mathrm{K}$ and in fields below $\sim 3\mathrm{T}$. The low temperature phase displays antiferromagnetic characteristics, while the nature of the ordering in the other phase(s) has yet to be determined.

Figure 1

(a) Magnetic susceptibility ${\chi }_{\mathrm{dc}}$ vs $T$, indicating a magnetic transition at $2.3\mathrm{K}$. (b) Inverse magnetic susceptibilility ${\chi }_{\mathrm{dc}}^{-1}$ vs $T$. The line represents a Curie-Weiss law, fit to the data above $50\mathrm{K}$. The inset shows the low-$T$ behavior of ${\chi }_{\mathrm{dc}}^{-1}\left(T\right)$ along with a different Curie-Weiss law fit (see text).

Figure 2

Magnetization $M$ vs $H$ isotherms at several values of $T$. Features in $M\left(H\right)$ at constant $T$, with $H_1$ and $H_2$ defined by a kink in $M\left(H\right)$, are illustrated for $T=0.425\mathrm{K}$. The inset shows $M\left(H\right)$ at higher temperatures.

Figure 3

Specific heat $C$ divided by $T$ vs $T$ (UCSD data). Inset (a) shows the transitions at $T_1$ and $T_2$ in more detail (UCSD data). Inset (b) shows the apparent resolution of the transition at $T_1$ into two transitions at $T_1$ and $T_1$’ (LLNL data).

Figure 4

(a) Zero field $C∕T$ vs $T^2$, with a linear best fit yielding the enhanced $\gamma$ and value of ${\Theta }_D$ given in the figure. (b) Magnetic entropy $S_m$ determined from the specific heat after the zero field lattice and electronic contributions to the specific heat were subtracted.

Figure 5

Electrical resistivity $\rho$ vs $T$ from $2\text{to}300\mathrm{K}$. The inset shows $\rho \left(T\right)$ from $0.06\text{to}25\mathrm{K}$.

Figure 6

(a) Schematic representation of the $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{As}}_{12}$ magnetic field–temperature $(H-T)$ phase diagram. The vertical and horizontal lines represent isothermal $M\left(H\right)$ and constant field $M\left(T\right)$ measurements as depicted in (b) and (c). (b) Magnetization $M$ vs $H$ at $0.425\mathrm{K}$, with features at $H_1$ and $H_2$ used to define the phase diagram. (c) Magnetization $M$ vs $T$ at $1.5\mathrm{T}$, along with two clear features at $T_1$ and $T_2$, used to contrast the phase diagram. (d) The derivative $dM∕dH$ as a function of $H$ indicates two features used to define $H_1$ and $H_2$ in Fig. 6b. The dotted lines represent estimated transition widths for $H_1$ and $H_2$.

Figure 7

Magnetic field-temperature $(H-T)$ phase diagram for $\mathrm{Pr}{\mathrm{Os}}_4{\mathrm{As}}_{12}$, as defined by features in the magnetization (Fig. 2) (circles and squares). The lines are guides to the eye.