Spin-charge-lattice coupling near the metal-insulator transition in ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$

We report x-ray scattering studies of the $c$-axis lattice parameter in ${\mathrm{Ca}}_3{\mathrm{Ru}}_2{\mathrm{O}}_7$ as a function of temperature and magnetic field. These structural studies complement published transport and magnetization data, and therefore elucidate the spin-charge-lattice coupling near the metal-insulator transition. Strong anisotropy of the structural change for field applied along orthogonal in-plane directions is observed. Competition between a spin-polarized phase that does not couple to the lattice and an antiferromagnetic metallic phase that does gives rise to a rich behavior for $\mathbf{B}\Vert b$.

Figure 1

Zero-field $\theta \text{−}2\theta$ scans through the (0 0 16) reflection as a function of temperature. Inset displays the scattering geometry.

Figure 2

Temperature dependence of the $c$-axis lattice parameter change—relative to its value at $T\approx 25\mathrm{K}$—in fixed $\mathbf{B}\Vert a$ (a) and $b$ (b) axes. Dashed lines in (b) are the limits used to determine the temperature range of the structural change (see Fig. 3).

Figure 3

(Color) Structural change phase diagram for $\mathbf{B}$ applied along the $a$ (●) and $b$ (엯) axes, and the lines are merely guides for the eyes. Labels, which are taken from Ref. 7, are for the sake of comparison and refer to paramagnetic metallic (PM), spin-flop (SF), antiferromagnetic nonmetallic (AFNM), and antiferromagnetic metallic (AFM) phases. Inset displays the field dependence of the $c$-axis lattice parameter change at $T=44.3\mathrm{K}$ for $\mathbf{B}\Vert b$.

Figure 4

(Color) Hysteresis curves as a function of $\mathbf{B}$ applied along the $b$ (엯 and ▵) and $a$ (●) axes. Inset displays the hysteresis curve for fixed $\mathbf{B}$ $(=5\mathrm{T})\Vert a$.