Pressure effects in the itinerant antiferromagnetic metal TiAu

We report the pressure dependence of the Néel temperature $T_N$ up to $P\approx 27$ GPa for the recently discovered itinerant antiferromagnet (IAFM) TiAu. The $T_N\left(P\right)$ phase boundary exhibits unconventional behavior in which the Néel temperature is enhanced from $T_N\approx 33$ K at ambient pressure to a maximum of $T_N\approx 35$ K occurring at $P\approx 5.5$ GPa. Upon a further increase in pressure, $T_N$ is monotonically suppressed to $\sim 22$ K at $P\approx 27$ GPa. We also find a crossover in the temperature dependence of the electrical resistivity $\rho$ in the antiferromagnetic (AFM) phase that is coincident with the peak in $T_N\left(P\right)$, such that the temperature dependence of $\rho ={\rho }_0+A_n{T}^n$ changes from $n\approx 3$ during the enhancement of $T_N$ to $n\approx 2$ during the suppression of $T_N$. Based on an extrapolation of the $T_N\left(P\right)$ data to a possible pressure-induced quantum critical point, we estimate the critical pressure to be $P_c\approx 45$ GPa.

Figure 1

(a) Electrical resistivity $\rho \text{vs}$ temperature $T$ at $P=0$ and 1.8 GPa as measured in a piston cylinder cell (PCC). The arrows indicate the features in $\rho$ that correspond to values of $T_N=32.7$ K and 35.5 K at $P=0$ and 1.77 GPa, respectively. Inset: Electrical resistivity $\rho \text{vs}T$ up to $T=200$ K at various pressures up to $P=1.8$ GPa displaying the nearly linear temperature dependence and metallic behavior of $\rho$ in the PM phase. The $\rho \text{vs}T$ curves have been shifted vertically for clarity in illustrating the increase in $T_N$ with increasing pressure. (b) The temperature derivative of the electrical resistivity $d\rho /dT\text{vs}$ temperature $T$ at various pressures (shifted vertically for clarity). The Néel temperature at each pressure was determined from the maximum in $d\rho /dT$ as indicated by the arrows, and the values of $T_N$ are listed in Table 1.

Figure 2

Electrical resistivity $\rho /{\rho }_{300\mathrm{K}}$ (a,c,e) and its temperature derivative $d\rho /dT$ (b,d,f), as a function of temperature for three different polycrystalline samples of TiAu, as measured in a Bridgman anvil cell (BAC) at various values of pressure. The arrows indicate the feature at the AFM ordering temperature with the values of $T_N$ extracted either from the maximum in $d\rho /dT$ or from the intersection of the linear extrapolations (solid black lines) of the $d\rho /dT\text{vs}T$ curves. The values of $T_N$ at various $P$ for TiAu samples 1, 2, and 3 measured in the two different Bridgman anvil cells are presented in Table 1.

Figure 3

(a) Electrical resistivity $\rho /{\rho }_{300\mathrm{K}}\text{vs}$ temperature $T$ in the vicinity of the AFM ordering temperature $T_N$ at various pressures up to $P\approx 27$ GPa as measured in a diamond anvil cell (DAC). The arrows point to the features at $T_N$. (b) Temperature derivative of the electrical resistivity $d\rho /dT\text{vs}T$. The values of $T_N=30.7$ and 32.2 K at $P=2.2$ and 5.0 GPa, respectively, were determined from the maximum in the $d\rho /dT\text{vs}T$ curves, whereas the values of $T_N=28.5$, 25.9, 24.7, and 22.1 K at $P=9.7$, 15.0, 18.1, and 26.7 GPa, respectively, were determined from the intersection of the linear extrapolations (solid black lines) of the $d\rho /dT\text{v}sT$ curves as shown in panel (b).

Figure 4

Scaled electrical resistivity $\rho /{\rho }_{300\mathrm{K}}\text{vs}{T}^n$ above and below the Néel temperature $T_N$ for TiAu under pressure $P$. Power-law fits of the electrical resistivity, $\rho ={\rho }_0+A_n{T}^n\mathrm{b}$ to the $\rho \left(T\right)$ data were performed for $T<T_N$ in the AFM phase (top eight panels with black symbols and a red fit line) and for $T>T_N$ in the PM phase (bottom eight panels with red symbols and a black fit line). The upper $x$ axis in each plot is shown as a linear $T$ scale, and $T_N$ is indicated by the black vertical arrows.

Figure 5

(a) Temperature $\text{vs}$ pressure ($T_N\text{vs}P$) phase diagram superimposed on a color contour representation of the exponent $n(P,T)$ from the electrical resistivity: $\rho ={\rho }_0+A_n{T}^n$ (see text). The solid black curve is a guide to the eye and denotes the $T_N\left(P\right)$ phase boundary. (b,c,d) The parameters $n, A_n$, and ${\rho }_0\text{vs}$ pressure $P$ were extracted from power-law fits of the electrical resistivity in the AFM phase as shown in Fig. 4. The dashed vertical line at $P=5.5$ GPa is a guide to the crossover at the peak in $T_N\left(P\right)$.

Figure 6

A plot of the $T_N\text{vs}$ residual resistivity ratio $\text{RRR}=\rho \left(300\text{K}\right)/\rho \left(2\text{K}\right)$ for the five TiAu samples measured in each of the various pressure cells at a low pressure of $P\approx 2–3\mathrm{GPa}$. Inset: Pressure coefficient $d{T}_N/dP$ during the enhancement of $T_N$ as pressure is increased up to $P\approx 6$ GPa for the five different TiAu samples.

Figure 7

(a) A temperature $\text{vs}$ pressure ($T_N\text{vs}P$) phase diagram for TiAu showing the extrapolated $T_N\left(P\right)$ boundary (dashed curve) toward a critical pressure $P_c$ at $T=0$ K. The critical scaling function $T_N=T_{N(P=0)}\times {(1-P/P_c)}^{\alpha }$ was fit to the $T_N$(P) data up to $P=27$ GPa. The ambient pressure value of the Néel temperature ($T_{N(P=0)}$) was set to 36 K, while a rough estimate of the value for the critical pressure was determined from the fit to be $P_c=45\pm 11$ GPa. The value for the scaling exponent $\alpha$ was determined from the fit to be $\alpha =0.65\pm 0.20$. The slope of the curve near $T_N=0$ K (represented by the solid black line) is $d{T}_N/dP\approx -2.5\text{K}{\mathrm{GPa}}^{-1}$, while the slope of the nearly linear $T_N$(P) data accumulated from the various pressure cells up to $P=27$ GPa is $d{T}_N/dP=-0.59\text{K}{\mathrm{GPa}}^{-1}$.