Magnetic Properties of Restacked 2D Spin 1/2 honeycomb RuCl₃ Nanosheets

Abstract

Spin 1 2 honeycomb materials have gained substantial interest due to their exotic magnetism and possible application in quantum computing. However, in all current materials out-of-plane interactions are interfering with the in-plane order, hence a true 2D magnetic honeycomb system is still of demand. Here, we report the exfoliation of the magnetic semiconductor α-RuCl 3 into the first halide monolayers and the magnetic characterization of the spin 1 2 honeycomb arrangement of turbostratically stacked RuCl 3 monolayers. The exfoliation is based on a reductive lithiation/hydration approach, which gives rise to a loss of cooperative magnetism due to the disruption of the spin 1 2 state by electron injection into the layers. After an oxidative treatment, cooperative magnetism similar to the bulk is restored. The oxidized pellets of restacked single layers feature a magnetic transition at T N = 7 K in the in-plane direction, while the magnetic properties in the out-of-plane direction vastly differ from bulk α-RuCl 3 . The macro- Binary halide nanosheets have been predicted based on chemical intuition 3,4 or ab initio calculations. 7 Yet, no single layer halides have been synthesized so far, even though this class of compounds features an array of interesting electrical and magnetic properties.The magnetic semiconductor α-RuCl 3 is one such example. While it was investigated in the past as a host for intercalants 8,9 and as a lithium ion conductor, 10 current research focuses on its magnetic properties. Due to its layered honeycomb structure of spin 1 2 Ru 3+ centers in combination with spin orbit coupling (SOC), it is one of the few known materials featuring a zigzag antiferromagnetic (AF) ground state below a temperature of T N1 = 8 K. [11][12][13] In the zigzag order, the magnetic moments form ferromagnetic (FM) zigzag chains, whose magnetization direction is opposed to the neighboring chains within the plane. Additionally, there is a further magnetic phase transition observed at T N2 = 14 K. The origin of this transition is currently still under debate. This type of ordering was first observed in Na 2 IrO 3 14-16 and explained by the Kitaev-Heisenberg model, 17,18 which describes that a frustrated spin 1 2 honeycomb arrangement could lead to a variety of interesting spin structures. Based on the competition among the exchange interactions up to the third neighbor, the system could possibly be pushed into a quantum spin liquid regime by the manipulation of the competing interactions, thereby opening up applications in quantum computing. 17,19 Yet, the Na + ions in the interlayer space of Na 2 IrO 3 lead to disadvantageous interactions between the iridate layers, which interfere with theoretical predictions of a honeycomb arrange-2 ment of spin 1 2 magnetic arrays. 20 Eliminating the interlayer interaction could provide a route to manipulate the spin structure of real materials featuring a spin 1 2 honeycomb arrangement. In RuCl 3 , where no charged ions are in between the honeycomb layers, the interlayer in...

Electronic and magnetic properties of monolayer α-RuCl3: a first-principles and Monte Carlo study

“…And also this result is comparable with those of the other MX 3 (M=Cr, V, Ti ; X=Cl, Br, I) materials. 23,28 Consequently, according to this result α-RuCl 3 monolayer can be obtained by the exfoliation process from its bulk phase whereas realized recently by Weber et al 47 Secondly, we obtain the monolayer α-RuCl 3 (see Figure 2(a)), and to confirm the dynamical stability of α-RuCl 3 we calculate the phonon frequencies (see Figure 2(b)) along the main symmetry directions in 2D Brillouin zone (BZ) by using the PHONOPY program, which is based on the finite-displacement method as implemented in VASP. 58 Our calculations show that there is not any negative frequencies in the BZ, which proved the dynamical stability at T∼0 K temperature.…”

“…Before studying the monolayer form of α-RuCl 3 , we first tested the possibility of exfoliation process to obtain monolayer from its bulk form. First, we created bulk α-RuCl 3 with a=5.99, b=10.37 and c=6.05Å lattice constants as illustrated in Figure 1 (suitable with literature 47,48,61 ) and we implemented a fracture in the bulk after four periodic layer and we systematically increase this fracture distance, at the end we calculate the corresponding cleavage energy (CE) (Figure 1). This method is very effective and has been widely confirmed.…”

“…Weber et al chemically exfoliated the monolayer α-RuCl 3 , but they did not clarify the magnetism of a suspended monolayer on SiO 2 /Si substrate. 47 In another study, Ziatdinov et al mentioned in their study that magnetic ground state can occurs in the geometry of the ligand sublattice in thin films of RuCl 3 .…”

Relation between Kitaev magnetism and structure in α−RuCl3

“…To date, only a handful of candidates are known to fulfill these criteria: the harmonic-honeycomb iridates α-, β-, and γ-Li 2 IrO 3 8-13 and the 4d 5 ruthenate α-RuCl 3 [14][15][16][17][18][19][20][21][22][23][24][25][26][27] . All these materials, however, exhibit long-range magnetic ordering, preempting a spin liquid state due to the presence of residual Heisenberg, off-diagonal, and longer-range interactions.…”

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].…”