Spin-stripe phase in a frustrated zigzag spin-1/2 chain

Stabilization of Short- and Long-Range Magnetic Ordering through the Cooperative Effect of 1D [CuO4]∞ Chains and [CuO2X2] Quadrilateral in Quasi-1D Spin-1/2 Systems

Quasi-1D chain antiferromagnets with reduced structural dimensionality are a rich playground for investigating novel quantum phenomena. We report the synthesis, crystal structure, and magnetism of two novel quasi-1D antiferromagnets, β-PbCu2(TeO3)2Cl2 (I) and PbCu2(TeO3)2Br2 (II). Their magnetic frameworks are constructed via Cu-based quasi-1D [Cu(2)O4]∞ zigzag chains with square-planar [Cu(1)O2X2] (X=Cl or Br) separated among 1D chains. Specific heat measurements show λ peaks at ~9 K and ~19 K for I and II, respectively. Moreover, both broad maximums (χmax=90 K for I and 80 K for II) and small kinks (TN≈9 K for I and 19 K for II) have been observed in magnetic susceptibility measurements of I and II. Bonner-Fisher model fitting, and theoretical analyses were performed to evaluate the magnetic exchange interactions. Our experimental and theoretical results and structure-properties relationship analysis reveal the coexistence of short- and long-range magnetic ordering from the cooperative effect of 1D [CuO4]∞ chains and [CuO2X2] quadrilateral.

KMB4O6F3 (M = Co, Fe): two-dimensional magnetic fluorooxoborates with triangular lattices directed by triangular BO3 units

Frustrated magnetic systems are of great interest owing to their spin liquid state for application in quantum computing. However, experimentally, spin liquid has not been realized. Thus, experimental explorations of frustrated magnetic systems including triangular lattices are still urgent, particularly for directed synthesis compared to random exploration. Herein, for the first time, directed by the use of a triangular unit of the BO3 anion group, two novel layered magnetic fluorooxoborates KMB4O6F3 (M = Co 1, Fe 2) with triangular lattices have been hydrothermally synthesized and characterized. Compounds 1 and 2 are isostructural and crystallize in the P21/c space group with layered magnetic triangular lattices, which are further separated by K+ ions. Magnetic susceptibility curves of both 1 and 2 show no λ-anomaly peak down to a low temperature of 2 K in the absence of a magnetic long-range ordering transition, which are further confirmed by the heat capacity results. The magnetic-field dependence of magnetization at 2 K shows saturation of 2.20μB for 1 and 4.24μB for 2, respectively, at 7 T, after roughly subtracting the Van Vleck paramagnetic contribution. Further in-depth investigation of the underlying physics at a lower temperature below 2 K would be subsequently performed. Moreover, thermal stability and FT-IR and UV-vis-NIR spectroscopy with optical bandgap properties are also reported. Most importantly, our work provides a promising method to experimentally realize specific magnetic lattices (e.g. triangular lattices) directed by the use of triangular groups (e.g. BO3) as the functional unit.

Gladstone-Dale compatibility, electronic polarizability and vibrational spectroscopy of minerals and inorganic compounds with V4+O and V4+O2 vanadyl groups

VO and VO2 vanadyl groups with short (typically 1.57-1.68 Å), essentially covalent, V-O bonds are common for V4+-bearing oxysalts with [5]- and [6]-coordinated vanadium. There is a clear negative correlation between vanadyl bond lengths and wavenumbers of the bands of V-O stretching vibrations in infrared spectra (in the range 1000-880 cm-1). Optical, structural and chemical data for vanadyl minerals are used to calculate Gladstone-Dale compatibility coefficients. Gladstone-Dale compatibility indices of minerals containing vanadyl bonds are compared with total electronic polarizabilities of V4+. Unlike compounds of [5]-coordinated Ti4+, for most minerals with V4+=O (vanadyl) bonds there is good agreement between measured refractive indices and those calculated based on the polarizability concept.

Chemical Vapor Transport Synthesis of Cu(VO)2(AsO4)2 With Two Distinct Spin-1/2 Magnetic Ions

A new copper vanadyl arsenate, Cu(VO)₂(AsO₄)₂, was synthesized via the chemical vapor transport method. Cu(VO)₂(AsO₄)₂ adopts an original structure type. It is characterized by layers formed by edge-sharing and corner-sharing V-centered octahedra resulting in a unique topology that was hitherto not reported for vanadates. Single CuO₆ octahedra connect vanadate layers into a rigid framework. The thermal expansion of the framework studied by the single-crystal HT X-ray diffraction is reported. The magnetic behavior of Cu(VO)₂(AsO₄)₂ shows an interplay of ferromagnetic V⁴⁺-V⁴⁺ and antiferromagnetic Cu²⁺-V⁴⁺ interactions that result in a ferrimagnetic long-range order below T_C = 66 K.

Magnon Pairs and Spin-Nematic Correlation in the Spin Seebeck Effect

Investigating exotic magnetic materials with spintronic techniques is effective at advancing magnetism as well as spintronics. In this work, we report unusual field-induced suppression of the spin Seebeck effect (SSE) in a quasi-one-dimensional frustrated spin-1/2 magnet LiCuVO_{4}, known to exhibit spin-nematic correlation in a wide range of external magnetic field B. The suppression takes place above |B|≳2  T in spite of the B-linear isothermal magnetization curves in the same B range. The result can be attributed to the growth of the spin-nematic correlation while increasing B. The correlation stabilizes magnon pairs carrying spin 2, thereby suppressing the interfacial spin injection of SSE by preventing the spin-1 exchange between single magnons and conduction electrons at the interface. This interpretation is supported by integrating thermodynamic measurements and theoretical analysis on the SSE.

Field-induced States and Excitations in the Quasicritical Spin-1/2 Chain Linarite

The mineral linarite, PbCuSO_{4}(OH)_{2}, is a spin-1/2 chain with frustrating nearest-neighbor ferromagnetic and next-nearest-neighbor antiferromagnetic exchange interactions. Our inelastic neutron scattering experiments performed above the saturation field establish that the ratio between these exchanges is such that linarite is extremely close to the quantum critical point between spin-multipolar phases and the ferromagnetic state. We show that the predicted quantum multipolar phases are fragile and actually suppressed by a tiny orthorhombic exchange anisotropy and weak interchain interactions in favor of a dipolar fan phase. Including this anisotropy in classical simulations of a nearly critical model explains the field-dependent phase sequence of the phase diagram of linarite, its strong dependence of the magnetic field direction, and the measured variations of the wave vector as well as the staggered and the uniform magnetizations in an applied field.

Quantum Lifshitz Field Theory of a Frustrated Ferromagnet

We propose a universal nonlinear sigma model field theory for one-dimensional frustrated ferromagnets, which applies in the vicinity of a "quantum Lifshitz point," at which the ferromagnetic state develops a spin wave instability. We investigate the phase diagram resulting from perturbations of the exchange and of magnetic field away from the Lifshitz point, and uncover a rich structure with two distinct regimes of different properties, depending upon the value of a marginal, dimensionless, parameter of the theory. In the regime relevant for one-dimensional systems with low spin, we find a metamagnetic transition line to a vector chiral phase. This line terminates in a critical end point, beyond which there is at least one multipolar or "spin nematic" phase. We show that the field theory is asymptotically exactly soluble near the Lifshitz point.