Successive magnetic phase transitions in $\mathbf{\alpha }$-RuCl${}_3$: XY-like frustrated magnet on the honeycomb lattice

Abstract

The layered compound $\alpha$-RuCl${}_3$ is composed of a honeycomb lattice of magnetic Ru${}^{3+}$ ions with the $4d^5$ electronic state. We have investigated the magnetic properties of $\alpha$-RuCl${}_3$ via magnetization and specific heat measurements using single crystals. It was observed that $\alpha$-RuCl${}_3$ undergoes a structural phase transition at $T_t\simeq 150$ K accompanied by fairly large hysteresis. This structural phase transition is expected to be similar to that observed in closely related CrCl${}_3$. The magnetizations and magnetic susceptibilities are strongly anisotropic, which mainly arise from the anisotropic $g$-factors, i.e., $g_{ab}\simeq 2.5$ and $g_c\simeq 0.4$ for magnetic fields parallel and perpendicular to the $ab$ plane, respectively. These $g$-factors and the obtained entropy indicate that the effective spin of Ru${}^{3+}$ is one-half, which results from the low-spin state. Specific heat data show that magnetic ordering occurs in four steps at zero magnetic field. The successive magnetic phase transitions should be ascribed to the competition among exchange interactions. The magnetic phase diagram for $H\parallel ab$ is obtained. We discuss the strongly anisotropic $g$-factors in $\alpha$-RuCl${}_3$ and deduce that the exchange interaction is strongly XY-like. $\alpha$-RuCl${}_3$ is magnetically described as a three-dimensionally coupled XY-like frustrated magnet on a honeycomb lattice.

10 pages, 14 figures, accepted for publication in Phys. Rev. B

References in corpus (5)

• $\alpha$-RuCl3: a Spin-Orbit Assisted Mott Insulator on a Honeycomb Lattice
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Cited by in corpus (2)

• Spin-wave excitations evidencing the Kitaev interaction in single crystalline $\alpha$-RuCl${}_3$
• Anisotropic Ru3+ 4d5 magnetism in the alpha-RuCl3 honeycomb system: susceptibility, specific heat and Zero field NMR