Magnetic order in α-RuCl3: A honeycomb-lattice quantum magnet with strong spin-orbit coupling

We report magnetic and thermodynamic properties of single crystal α-RuCl3, in which the Ru3+(4d5) ion is in its low spin state and forms a honeycomb lattice. Two features are observed in both magnetic susceptibility and specific heat data; a sharp peak at 7 K and a broad hump near 10–15 K. In addition, we observe a metamagnetic transition between 5 and 10 T. Our neutron diffraction study of single crystal samples confirms that the low …