Successive magnetic phase transitions inα−RuCl3: XY-like frustrated magnet on the honeycomb lattice

Abstract

The layered compound α-RuCl3 is composed of a honeycomb lattice of magnetic Ru 3+ ions with the 4d 5 electronic state. We have investigated the magnetic properties of α-RuCl3 via magnetization and specific heat measurements using single crystals. It was observed that α-RuCl3 undergoes a structural phase transition at Tt ≃ 150 K accompanied by fairly large hysteresis. This structural phase transition is expected to be similar to that observed in closely related CrCl3. The magnetizations and magnetic susceptibilities are strongly anisotropic, which mainly arise from the anisotropic g-factors, i.e., g ab ≃ 2.5 and gc ≃ 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 ab is obtained. We discuss the strongly anisotropic g-factors in α-RuCl3 and deduce that the exchange interaction is strongly XY-like. α-RuCl3 is magnetically described as a three-dimensionally coupled XY-like frustrated magnet on a honeycomb lattice.

Crystal structure and magnetism inα−RuCl3: Anab initiostudy

“…Note that, the C2/m structure was reported also as the space group of this compound 6,22 , and is similar to the P 3 1 12 structure. The major difference in two structures is the c-axis ordering of the Ru honeycomb layers, where in the C2/m unit cell three Ru layers are related by translation by (a + a + c)/3 while in the P 3 1 12 cell they are related by threefold screw axis.…”

“…It is also interesting that, the Cmc2 1 structure (with cFM order) shows the lowest energy, which can be transformed into other structures by applying mirror operations to every other RuCl 3 layers. One can speculate that the Cmc2 1 structure forms in high temperature regime and freeze below T ∼ 150 K, where an anomalous behavior in magnetic susceptibility observed 5,6 , so contributing to the magnetic peak with two-layer periodicity in polycrystalline samples below T N 1 14 K 5,7,11 . Finally, we comment on the interlayer exchange interactions.…”

“…Furthermore, α-RuCl 3 has a three-dimensional crystal structure consisting of RuCl 3 layer stacking, and interlayer coupling and interaction terms can introduce another complication. Experimentally, both P 3 1 12 and C2/m space groups have been suggested as the crystalline symmetry in this compound 3,6,11,21,22 . As an illustrative example, Fig.…”

“…One promising candidate is α-RuCl 3 , where edge-sharing RuCl 6 octahedra form two-dimensional RuCl 3 layers in which Ru honeycomb layers reside [3][4][5][6][7][8][9][10][11] . Compared to its 5d transition metal oxide counterparts α-A 2 IrO 3 (A=Li,Na) [12][13][14][15][16] , α-RuCl 3 has closer-to-ideal RuCl 6 octahedra 3 , so it was proposed as an excellent platform to explore the Kitaev physics and related magnetism despite weaker SOC 4,9,11,17,18 .…”

Field-induced quantum criticality in the Kitaev system α−RuCl3

“…We relate the data to theoretical calculations based on a J 1 -K 1 -1 -J 3 honeycomb model. Mott insulator with a layered structure of edge-sharing RuCl 6 octahedra arranged in a honeycomb lattice [1][2][3][4][5][6][7][8]. It has been suggested [9,10] that strongly spin-orbit-coupled Mott insulators with that lattice geometry realize bond-dependent magnetic "compass" interactions [11], which, if dominant, would lead to a quantum spin-liquid (QSL) ground state as discussed by Kitaev [12].…”