Structural phase transition in $\text{Ba}{\left({\text{Fe}}_{0.973}{\text{Cr}}_{0.027}\right)}_2{\text{As}}_2$ single crystals

We present thermodynamic, structural, and transport measurements on $\text{Ba}{\left({\text{Fe}}_{0.973}{\text{Cr}}_{0.027}\right)}_2{\text{As}}_2$ single crystals. All measurements reveal sharp anomalies at $\sim 112\text{K}$. Single crystal x-ray diffraction identifies the structural transition as a first order, from the high-temperature tetragonal $I4/mmm$ to the low-temperature orthorhombic $Fmmm$ structure, in contrast to an earlier report.

Figure 1

(Color online) Anisotropic, temperature-dependent susceptibility for $\text{Ba}{\left({\text{Fe}}_{0.973}{\text{Cr}}_{0.027}\right)}_2{\text{As}}_2$ single crystals. Inset shows anisotropic field-dependent magnetization at $T=1.85\text{K}$.

Figure 2

(Color online) Temperature-dependent resistivity for $\text{Ba}{\left({\text{Fe}}_{0.973}{\text{Cr}}_{0.027}\right)}_2{\text{As}}_2$ single crystals. Insets show hysteresis at the phase transition (left) and magnetoresistivity for $H\parallel c$, $I\parallel ab$ (right).

Figure 3

(Color online) Temperature-dependent Hall resistivity $\left({\rho }_H/H\right)$ for $H\parallel c$. Inset shows field-dependent Hall resistivity.

Figure 4

Temperature-dependent heat capacity for $\text{Ba}{\left({\text{Fe}}_{0.973}{\text{Cr}}_{0.027}\right)}_2{\text{As}}_2$ single crystals. Insets show low-temperature heat capacity plotted as $C_p/T$ vs $T^2$ (left) and enlarged transition region (right).

Figure 5

(Color online) Anisotropic, temperature-dependent thermal expansivity (lower panel), and thermal expansion coefficient (upper panel) of $\text{Ba}{\left({\text{Fe}}_{0.973}{\text{Cr}}_{0.027}\right)}_2{\text{As}}_2$. Inset to the upper panel shows the thermal expansion coefficient near $T_{sm}$.

Figure 6

(Color online) (a) $\left(\xi \xi 0\right)$ scans through the position of the tetragonal (1 1 10) reflection for temperatures close to the tetragonal-to-orthorhombic transition and for decreasing temperatures. The offset between every data set is 100 counts. The lines represent fit to the data to obtain the reflection positions and corresponding orthorhombic splitting, $\left(a-b\right)/\left(a+b\right)$, shown in (b). In (b), closed (green) and open (red) circles represent orthorhombic splitting during decreasing and increasing temperature scans, respectively. The error bar for the orthorhombic splitting is less than the symbol size and not shown.