Phase diagram of an asymmetric spin ladder

Coexistence of Two Spin Frustration Pathways in the Quantum Spin Liquid Ca10Cr7O28

Kagome antiferromagnetic lattices are of high interest because the geometric frustration is expected to give rise to highly degenerated ground states that may host exotic properties such as quantum spin liquid (QSL). Ca₁₀Cr₇O₂₈ has been reported to display all the features expected for a QSL. At present, most of the literature reports on samples synthesized with starting materials ratio CaO/Cr₂O₃ 3:1, which leads to a material with small amounts of CaCrO₄ and CaO as secondary phases; this impurity excess affects not only the magnetic properties but also the structural ones. In this work, samples with starting material ratios CaO/Cr₂O₃ 3:1, 2.9:1, 2.85:1, and 2.8:1 have been synthesized and studied by X-ray diffraction with Rietveld refinements, selected area electron diffraction measurements, high-resolution transmission electron microscopy (HRTEM), low-temperature magnetometry, and magnetic calorimetry. This result shows that a highly pure Ca₁₀Cr₇O₂₈ phase is obtained for a CaO/Cr₂O₃ ratio of 2.85:1 instead of the 3:1 usually reported; the incorrect stoichiometric ratio leads to a larger distortion of the corner-sharing triangular arrangement of magnetic ions Cr⁺⁵ with S = 1/2 in the Kagome lattice. In addition, our study reveals that there exists another frustration pathway which is an asymmetric zigzag spin ladder along the directions [211], [12–1], and [1–1–1], in which the Cr–Cr distances are shorter than in the Kagome layers.

This work represents the endeavor to ensure the correct stoichiometric composition of the quantum spin liquid material Ca₁₀Cr₇O₂₈. The synthesis and characterization addressed several nonstoichiometric samples, including impurities’ influence on the crystal structure and properties of Kagome and zigzag magnetic interaction. The characterization aspects of the compound are based on the X-ray diffraction data and Rietveld refinement. Further characterization could help us understand the nature of quantum material and aid in the additional development of quantum theories and technology.

Thermal properties of rung-disordered two-leg quantum spin ladders: Quantum Monte Carlo study

A two-leg quenched random bond disordered antiferromagnetic spin-1/2 Heisenberg ladder system is investigated by means of stochastic series expansion quantum Monte Carlo (QMC) method. Thermal properties of the uniform and staggered susceptibilities, the structure factor, the specific heat, and the spin gap are calculated over a large number of random realizations in a wide range of disorder strength. According to our QMC simulation results, the considered system has a special temperature point at which the specific heat takes the same value regardless of the strength of the disorder. Moreover, the uniform susceptibility is shown to display the same character except for a small difference in the location of the special point. Finally, the spin gap values are found to decrease with increasing disorder parameter and the smallest gap value found in this study is well above the weak coupling limit of the clean case.