Magnetic order in $\alpha$-RuCl$_3$: a honeycomb lattice quantum magnet with strong spin-orbit coupling

摘要

We report magnetic and thermodynamic properties of single crystal$\alpha$-RuCl$_3$, in which the Ru$^{3+}$ ($4d^5$) ion is in its low spin stateand forms a honeycomb lattice. Two features are observed in both magneticsusceptibility and specific heat data; a sharp peak at 7~K and a broad humpnear 10-15K. In addition, we observe a metamagnetic transition between 5~T and10~T. Our neutron diffraction study of single crystal samples confirms that thelow temperature peak in the specific heat is associated with a magnetic orderwith unit cell doubling along the honeycomb (100) direction, which isconsistent with zigzag order, one of the types of magnetic order predictedwithin the framework of the Kitaev-Heisenberg model.