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.

Magnetic resonance imaging (MRI) scans for bladder cancer are becoming more common and may provide accurate information that helps improve patient care. Here, we describe a standardized reporting criterion for bladder MRI. This should improve communication between doctors and allow better comparisons between patients.

High-field magnetization measurements up to 57 T have been performed at 0.08 K in a single crystal of a two-dimensional spin-gap material SrCu 2 (BO 3 ) 2 . We successfully observed the predicted plateau at 1/3 of the total magnetization around 50 T, in which the magnetic superstructure is characterized by a novel stripe order of triplets. The 1/3 plateau is much wider than the previously observed 1/4 and 1/8 plateaux.

Magnetic properties of the spin-1/2 kagome-like compound volborthite are studied using a high-quality polycrystalline sample. It is evidenced from magnetization and specific heat measurements that the spins on the kagome lattice still fluctuate at low temperature, down to T = 60 mK that corresponds to 1/1500 of the nearest-neighbor antiferromagnetic interaction, exhibiting neither a conventional long-range order nor a spin gap. In contrast, 51 V NMR experiments revealed a sharp peak at 1 K in relaxation rate, which indicates that a certain exotic order occurs. Surprisingly, we have observed three "steps" in magnetization as a function of magnetic field, suggesting that at least four liquid-like or other quantum states exist under magnetic fields.KEYWORDS: kagome lattice, spin liquid, magnetization step, volborthite * E-mail address: hiroi@issp.u-tokyo.ac.jpThe magnetic properties of materials arise from the collective interaction of electron spins on atoms in a crystal. The antiferromagnetic interaction often causes long-range order (LRO) in an alternating up-down pattern called the Néel order at low temperatures. However, such LRO can be destroyed completely on trianglular lattices, because the antiferromagnetic interaction is inevitably frustrated on each triangle, suppressing a unique arrangement of spins covering the whole lattice.1, 2) It is expected therefore that the system remains "liquid", called the spin liquid, instead of a Néel order down to the lowest temperature. Since quantum fluctuations should play a crucial role in such a quantum disordered state, one would expect a new state of matter with properties we have never encountered. 3)Moreover, a quantum spin liquid might have exotic excitations or adopt a certain type of subtle order, such as a topological order. 4)Although an extensive study has been carried out to search for this mysterious state, clear experimental evidence has remained elusive until recently. 3,4) One famous candidate for a quantum spin liquid is a resonating-valence-bond (RVB) state on a triangular lattice postulated theoretically by Anderson in 1973. 5)Instead of an ordinary Néel state with LRO, the RVB state consists of paired spins with zero total quantum spin number, such as the configurations on a kagome lattice depicted in Fig.1(a). Since the ground state is defined quantum mechanically as a linear combination of all possible configurations derived from different pairings, a liquid-like behavior is expected even at T = 0. 6)A kagome lattice made of vertex-sharing triangles is one of the typical playgrounds for frustration physics.7) The theoretical ground state for the spin-1/2 kagome antiferromagnet (KAFM) is in fact an RVB state with an energy gap called the spin gap in the excitation spectrum. 1,8,9) This is because in the RVB picture, an excitation results from breaking spin singlet pairs: the larger the magnetic coupling, the larger the spin gap. Since the predicted magnitude of the spin gap Δ is small, J / 4 or J / 20, where J is the magnitude of the nearest-neigh...