Hexagonal α-Ru trichloride single crystals exhibit a strong magnetic anisotropy and we show that upon applying fields up to 14 T in the honeycomb plane the successive magnetic order at T1 = 14 K and T2 = 8 K could be completely suppressed whereas in the perpendicular direction the magnetic order is robust. Furthermore the field dependence of χ(T) implies coexisting ferro-and antiferromagnetic exchange between in-plane components of Ru 3+ -spins, whereas for out-of-plane components a strong antiferromagnetic exchange becomes evident. 101 Ru zero-field nuclear magnetic resonance in the ordered state evidence a complex (probably non coplanar chiral) long-range magnetic structure. The large orbital moment on Ru 3+ is found in density-functional calculations. PACS numbers: 75.30.Gw, 75.40.Cx, Low dimensional 4d-and 5d-magnets show a wide variety of magnetic ground states due to crystal electric field (CEF) splitting in combination with a strong spin-orbit coupling (SOC). Especially the 5d 5 -iridate compounds earned great attention because of the predicted topological Mott insulating state due to the strong SOC and the Coulomb correlation [1]. Furthermore the strong SOC favors the asymmetric Dzyaloshinskii-Moriya (DM) interaction that often results in chiral spin arrangements in the ordered phases [2,3]. In addition, for spin-1/2 systems geometrical frustration of the magnetic exchange interactions frequently leads to a quantum spin-liquid ground state[4]. Among 4d-and 5d-systems, the Heisenberg-Kitaev model (HKM) was established to describe the competing bond-dependent magnetic exchange interactions in the honeycomb type of lattice structures [5]. Prominent examples are the 2-1-3 iridates (Li 2 IrO 3 , Na 2 IrO 3 ) where the magnetism is associated to the 5d 5 electrons on the Ir 4+ ions. According to the HKM, the phase diagram provides a transition from a conventional Neel-type of antiferromagnetic (AFM) order to a AFM stripy-(or zigzag-) type of order towards a pure quantum spin liquid (QSL) phase as a function of control parameter [6]. Indeed Na 2 IrO 3 shows an AFM order of zigzag-type at T = 15 K, whereas the Li 2 IrO 3 system is more close to the QSL regime and a non coplanar spiral order is discussed [7].In order to search for new 4d-or 5d-model system with the honeycomb lattice arrangement as a platform of HKM α-RuCl 3 turns out to be an excellent candidate because the low spin 3+ state of Ru (4d 5 ) is equivalent to the low spin 4+ state of Ir (5d 5 ). However, lowtemperature magnetic properties of α-RuCl 3 were not studied in detail and, so far, on powders only. Recently, Plumb and co-workers have shown in a spectroscopic experiment that α-RuCl 3 is a magnetic insulator due to sizable Coulomb correlations accompanied by the spinorbit coupling [8].In this Rapid Communication, we report detailed studies on the magnetic anisotropy by magnetization and specific heat on single crystals over a wide temperature and field range. Furthermore, we applied 99,101 Ru zero-field nuclear magnetic resonance as a local and ...

Temperature-pressure phase diagram of the Kitaev hyperhoneycomb iridate β-Li_{2}IrO_{3} is explored using magnetization, thermal expansion, magnetostriction, and muon spin rotation measurements, as well as single-crystal x-ray diffraction under pressure and ab initio calculations. The Néel temperature of β-Li_{2}IrO_{3} increases with the slope of 0.9  K/GPa upon initial compression, but the reduction in the polarization field H_{c} reflects a growing instability of the incommensurate order. At 1.4 GPa, the ordered state breaks down upon a first-order transition, giving way to a new ground state marked by the coexistence of dynamically correlated and frozen spins. This partial freezing in the absence of any conspicuous structural defects may indicate the classical nature of the resulting pressure-induced spin liquid, an observation paralleled to the increase in the nearest-neighbor off-diagonal exchange Γ under pressure.

Detailed magnetization, specific heat, and 7 Li nuclear magnetic resonance (NMR) measurements on single crystals of the hyperhoneycomb Kitaev magnet β-Li2IrO3 are reported. At high temperatures, anisotropy of the magnetization is reflected by the different Curie-Weiss temperatures for different field directions, in agreement with the combination of a ferromagnetic Kitaev interaction (K) and a negative off-diagonal anisotropy (Γ) as two leading terms in the spin Hamiltonian. At low temperatures, magnetic fields applied along a or c have only a weak effect on the system and reduce the Néel temperature from 38 K at 0 T to about 35.5 K at 14 T, with no field-induced transitions observed up to 58 T on a powder sample. In contrast, the field applied along b causes a drastic reduction in the TN that vanishes around Hc = 2.8 T giving way to a crossover toward a quantum paramagnetic state. 7 Li NMR measurements in this field-induced state reveal a gradual line broadening and a continuous evolution of the line shift with temperature, suggesting the development of local magnetic fields. The spin-lattice relaxation rate shows a peak around the crossover temperature 40 K and follows power-law behavior below this temperature. arXiv:1906.09089v2 [cond-mat.str-el]

2017) S=12 quantum critical spin ladders produced by orbital ordering in Ba2CuTeO6. Physical Review B, 95 (10).

dc magnetization and 31 P spin lattice relaxation rate in the polycrystalline sample of LaCoPO suggest a spin fluctuation dominated ferromagnetically ordered state. Moreover, NMR data clearly indicate a crossover from 2D to 3D spin fluctuations across TC. In contrast to isotropic hyperfine field, H hf at the 31 P site in LaFePO, H hf is anisotropic in LaCoPO. The data of spin lattice relaxation rate also exhibit anisotropic spin fluctuation. The anisotropy vanishes near TC.