CdCu3(OH)6Cl2: A new layered hydroxide chloride

Ba4Ni3F14·H2O: a ferrimagnetic compound with a staircase kagomé lattice

A new crystalline fluoride Ba₄Ni₃F₁₄·H₂O was found to exhibit a rare S = 1 staircase kagomé lattice built by Ni²⁺ ions. Magnetic measurements indicate a ferrimagnetic transition at ∼28 K, while 1/3 plateau can be observed from the magnetization curve. We suggest that the hydrogen-bond interactions of O-H⋯F pathways may play an important role for magnetic properties of the system.

Ground-State Spin Dynamics in d1 Kagome-Lattice Titanium Fluorides

Many quantum magnetic materials suffer from structural imperfections. The effects of structural disorder on bulk properties are difficult to assess systematically from a chemical perspective due to the complexities of chemical synthesis. The recently reported S = 1/2 kagome lattice antiferromagnet, (CH₃NH₃)₂NaTi₃F₁₂, 1-Ti, with highly symmetric kagome layers and disordered interlayer methylammonium cations, shows no magnetic ordering down to 0.1 K. To study the impact of structural disorder in the titanium fluoride kagome compounds, (CH₃NH₃)₂KTi₃F₁₂, 2-Ti, was prepared. It presents no detectable structural disorder and only a small degree of distortion of the kagome lattice. The methylammonium disorder model of 1-Ti and order in 2-Ti were confirmed by atomic-resolution transmission electron microscopy. The antiferromagnetic interactions and band structures of both compounds were calculated based on spin-polarized density functional theory and support the magnetic structure analysis. Three spin-glass-like (SGL) transitions were observed in 2-Ti at 0.5, 1.4, and 2.3 K, while a single SGL transition can be observed in 1-Ti at 0.8 K. The absolute values of the Curie-Weiss temperatures of both 1-Ti (-139.5(7) K) and 2-Ti (-83.5(7) K) are larger than the SGL transition temperatures, which is indicative of geometrically frustrated spin glass (GFSG) states. All the SGL transitions are quenched with an applied field >0.1 T, which indicates novel magnetic phases emerge under small applied magnetic fields. The well-defined structure and the lack of structural disorder in 2-Ti suggest that 2-Ti is an ideal model compound for studying GFSG states and the potential transitions between spin liquid and GFSG states.

Strong spin frustration and negative magnetization in LnCu3(OH)6Cl3 (Ln = Nd and Sm) with triangular lattices: the effects of lanthanides

Herbertsmithite- and kapellasite-type compounds with triangular lattices (i.e. Kagomé) as the most promising candidates for realizing the exotic quantum spin liquid (QSL) state have recently attracted significant attention in condensed matter physics and materials science but are often adversely affected by dimensional imperfections arising from significant cation mixing. Also, interaction mechanisms between the Kagomé lattices and ionic impurities remain unclear. Herein we report on the synthesis, crystal structures and magnetic properties of a new class of kapellasite-type compounds LnCu₃(OH)₆Cl₃ (Ln = Nd and Sm) with two overlapped triangular lattices. These compounds are characterized by the triangular lattices of Cu²⁺ superimposed by another triangular lattice of paramagnetic Ln³⁺. The magnetic properties of LnCu₃(OH)₆Cl₃ feature strong spin frustrations as well as antisymmetrical Dzyaloshinskii-Moriya interactions resulting in canted antiferromagnetic ordering with the Néel temperature (T_N) of ∼20 K and ∼18 K for NdCu₃(OH)₆Cl₃ and SmCu₃(OH)₆Cl₃, respectively. Moreover, negative magnetization at low temperatures was firstly observed in Kagomé lattice compounds, arising from geometrical spin frustration and competing interactions within two overlapped triangular lattices.

Prospect of quantum anomalous Hall and quantum spin Hall effect in doped kagome lattice Mott insulators

Electronic states with non-trivial topology host a number of novel phenomena with potential for revolutionizing information technology. The quantum anomalous Hall effect provides spin-polarized dissipation-free transport of electrons, while the quantum spin Hall effect in combination with superconductivity has been proposed as the basis for realizing decoherence-free quantum computing. We introduce a new strategy for realizing these effects, namely by hole and electron doping kagome lattice Mott insulators through, for instance, chemical substitution. As an example, we apply this new approach to the natural mineral herbertsmithite. We prove the feasibility of the proposed modifications by performing ab-initio density functional theory calculations and demonstrate the occurrence of the predicted effects using realistic models. Our results herald a new family of quantum anomalous Hall and quantum spin Hall insulators at affordable energy/temperature scales based on kagome lattices of transition metal ions.

Barlowite: A Spin-1/2 Antiferromagnet with a Geometrically Perfect Kagome Motif

We present thermodynamic studies of a new spin-1/2 antiferromagnet containing undistorted kagome lattices-barlowite Cu_{4}(OH)_{6}FBr. Magnetic susceptibility gives θ_{CW}=-136  K, while long-range order does not happen until T_{N}=15  K with a weak ferromagnetic moment μ<0.1μ_{B}/Cu. A 60 T magnetic field induces a moment less than 0.5μ_{B}/Cu at T=0.6  K. Specific-heat measurements have observed multiple phase transitions at T≪∣θ_{CW}∣. The magnetic entropy of these transitions is merely 18% of k_{B}ln2 per Cu spin. These observations suggest that nontrivial spin textures are realized in barlowite with magnetic frustration. Comparing with the leading spin-liquid candidate herbertsmithite, the superior interkagome environment of barlowite sheds light on new spin-liquid compounds with minimum disorder. The robust perfect geometry of the kagome lattice makes charge doping promising.