Moessbauer spectroscopy and magnetization studies of .alpha.- and .beta.-ruthenium trichloride

Low-temperature crystal and magnetic structure ofα−RuCl3

“…Further deforming the crystal altogether obliterates the magnetic transition at 7 K (brown curve-3). The transition at 14 K is broad, and matches the magnetic transition in a powder sample (blue curve-4) with an ABAB type magnetic order [19,21,23,24] as well as single crystals reported in Ref. [20].…”

“…The single ion ground state is confirmed as effective J=1/2 [18][19][20][21] and interestingly both inelastic neutron scattering [21] and Raman scattering [17] show evidence for continuum magnetic response that could be associated with fractionalized excitations. Neutron diffraction studies [16,20,21] have shown that the materials order in-plane with a zigzag spin structure which can arise from the Kitaev-Heisenberg model [25] as well as Kitaev-dominated models with additional more complicated interactions [26][27][28].…”

“…The challenges presented by the large neutron absorption cross-section and rapid decrease of the Ir magnetic form factor have limited the neutron studies of honeycomb iridates to date [13][14][15]. On the other hand, it is much more feasible to carry out detailed neutron scattering investigations of the binary halide α-RuCl 3 , which has been proposed as an alternate candidate to realize Kitaev physics [16][17][18][19][20][21][22]. In this material, honeycomb layers of octahedrally coordinated low spin Ru 3+ ions are coupled via weak van der Waals inter-layer interactions [23,24] (see Fig.…”

“…The low temperature magnetic ordering transitions have similarly shown some discrepancies. Specific heat and susceptibility measurements on powders [18][19][20][21] have consistently shown a broad Néel transition at 14 K, however many previously investigated single-crystals show evidence for two separate Néel transitions at T N = 8 K and 14 K, and perhaps others [21], with some suggestions that these are associated with exotic physics [16,22]. A previous neutron diffraction study of single crystals with stacking faults indicated by a broad mosaicity in the direction perpendicular to the honeycomb planes [21] showed (using T nomenclature) that the 14 K transition is associated with a (1/2, 0, 3/2) T ordering wave vector corresponding to a bilayer ABAB antiferromagnetic stacking, while the 8 K transition is associated with a (1/2, 0, 1) T wave vector indicating ABC periodicity (see the transformation matrix in the note [33]).…”

Crystal and Magnetic Structures in Layered, Transition Metal Dihalides and Trihalides

“…Magnetization measurements in the paramagnetic state have been reported for both powder and single crystals. Powder measurements give effective moments of 2.2-2.3 µ B and Weiss temperatures of 23-40 K [13,81,141,142]. Single crystal measurements show strong paramagnetic anisotropy, and give µ e f f = 2.1 µ B and θ = 37 K with the field applied in the plane, and µ e f f = 2.7 µ B and θ = −150 K with the field applied perpendicular to the layers [143].…”