Phase transition in the $5d^1$ double perovskite ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ induced by high magnetic field

Magnetic properties of an antiferromagnetic double perovskite oxide ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$, where ${\mathrm{Re}}^{6+}$ $\left(5d^1\right)$ ions with large spin-orbit coupling are arranged on the face-centered-cubic lattice, are investigated using pulsed high magnetic field up to 66 T. Magnetization and magnetostriction measurements have revealed a magnetic field-induced phase transition at around 50 T. The phase transition accompanies a jump of magnetization and longitudinal magnetostriction of approximately $2\times {10}^{–4}$ with the change of power-law behavior, indicating sizable coupling between the electronic degrees of freedom and the lattice. The high-field phase exhibits a magnetic moment approximately 0.2 ${\mu }_{\mathrm{B}}$, which is close to the values observed in $5d^1$ double perovskite oxides with noncollinear magnetic structure. We argue that ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ is an antiferromagnet that sits close to the phase boundary between the collinear and noncollinear phases, providing the target material for investigating the interplay between spin-orbital entangled electrons and magnetic field.

Figure 1

(a) Temperature dependence of magnetic susceptibility M/H (red) and the inverse susceptibility H/M (blue) of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$. The cubic-tetragonal transition at $T_s=130\mathrm{K}$ and the magnetic transition at $T_m=16\mathrm{K}$ are indicated by the arrows. The dashed and solid lines indicate the linear fits at 150–350 K and 50–120 K, respectively.

Figure 2

Linear thermal expansion $\mathrm{\Delta }L/L_{297\mathrm{K}}$ of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$. The data around $T_m$ are shown in the upper inset. The crystal structure below $T_s$ depicted by vesta [27] is shown in the lower inset. The O atoms at the axial and equatorial position in the ${\mathrm{ReO}}_6$ octahedra (red) are shown by blue and green spheres, respectively.

Figure 3

(a) Temperature dependence of the specific heat divided by temperature $C_p/T$ of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ (red) and its nonmagnetic analog ${\mathrm{Ba}}_2{\mathrm{CaWO}}_6$ (black). The electronic entropy $S_{\mathrm{e}}$ estimated as shown in the main text is shown in the inset. (b) $C_p/T$ of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ below 30 K measured for different samples (No. 1 and No. 2). The lattice specific heat estimated by rescaling the data of ${\mathrm{Ba}}_2{\mathrm{CaWO}}_6$ is shown by the gray solid line for the sample No. 1. $C_p/T$ of the sample No. 2 is measured at 0 and 5 T: the data are shown with offsets.

Figure 4

(a) Magnetization curves of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ measured up to 66 T (red) at 4.2 K and those of ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$ (blue) and ${\mathrm{Sr}}_2{\mathrm{MgReO}}_6$ (black) measured up to 51 T at 1.4 K. The magnetization curves measured with smaller maximum magnet fields are shown for ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ and ${\mathrm{Ba}}_2{\mathrm{MgReO}}_6$. The high-field data are corrected so as to coincide with the low-field SQUID data. The gray dashed line on the magnetization curve of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ is the linear fits at selected magnetic field ranges. (b) Temperature dependence of the magnetization curve of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ measured up to 56 T (left) and (c) its magnetic field derivative dM/dH. The data are shown with offsets along the vertical axis. The peaks of dM/dH in increasing and decreasing fields are marked by the filled and unfilled arrows, respectively. The dashed line on the data at 14 K is a guide for the eyes.

Figure 5

Magnetostriction $\mathrm{\Delta }L/L_{0\mathrm{T}}$ of ${\mathrm{Ba}}_2{\mathrm{CaReO}}_6$ measured at 4.2 K. Data measured in the increasing and decreasing field processes are shown. Two datasets for different epoxy composite samples are shown. The magnetostriction with positive and negative values correspond to the longitudinal and transverse magnetostriction, respectively. The data are shown with the offsets along the vertical axis. The longitudinal magnetostriction is plotted against the magnetization in the inset. The black and gray lines in the inset are the fit to the power law $\mathrm{\Delta }L/L_{0\mathrm{T}}\propto M^2$ and $M^{0.5}$, respectively.