Magnetic-Field Induced Transition to the $1/2$ Magnetization Plateau State in the Geometrically Frustrated Magnet $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$

The magnetization of the geometrically frustrated spinel $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$ was measured in pulsed fields of up to 47 T. We found a metamagnetic transition to a very wide magnetization plateau state with one half of the full moment of $S=3/2$ ${\mathrm{C}\mathrm{r}}^{3+}$ at 28 T, independent of the field direction. This is the first observation of magnetization plateau state realized in Heisenberg pyrochlore magnet. The plateau state can be ascribed to a collinear spin configuration with three-up and one-down spins out of four spins of each Cr tetrahedron. A large magnetostriction is observed at the transition in spite of the negligible spin-orbit couplings. We argue that spin frustration plays a vital role in this large spin-lattice coupling.

Figure 1

Temperature dependence of magnetic susceptibility of $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$ single crystal. The data for $\mathrm{Z}\mathrm{n}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$ polycrystalline sample is also shown for comparison. The inset demonstrates the anisotropy of the magnetic susceptibility in the tetragonal phase of $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$.

Figure 2

Magnetization curves of $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$ single crystal in fields of up to 47 T, taken at a temperature of 1.8 K. Magnetic fields are applied along [100], [110], and [111] in cubic indices. The curves are shifted to avoid overlapping. The inset shows longitudinal (along [111]) and transversal (along $[1\overline{1}0]$) magnetostriction measured at 4.2 K, when a magnetic field is applied along the [111] direction of the crystal. Magnetization curve for $\mathrm{Z}\mathrm{n}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$ polycrystalline sample is shown for comparison in the main panel.

Figure 3

Magnetization curves $M(H)$ of $\mathrm{C}\mathrm{d}{\mathrm{C}\mathrm{r}}_2{\mathrm{O}}_4$ for $H\parallel [111]$ taken at various temperatures. The inset shows the $H$-$T$ phase diagram in fields of up to 47 T, as found by $M(H)$ measurements using pulsed fields, and $M(T)$ measurement below 12 T.