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Magnetothermal properties of the Heisenberg-Ising orthogonal-dimer chain with triangular XXZ clusters

机译：具有三角形XXZ簇的Heisenberg-Ising正交二聚体链的磁热性质

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摘要

We study a spin-1/2 model with triangular XXZ clusters on the orthogonal-dimer chain in the presence of an external magnetic field. First, we discuss the case where the triangular clusters are coupled via intermediate "classical" Ising spins. Diagonalization of the triangular XXZ clusters yields the exact ground states; finite-temperature properties are computed exacdy by an additional transfer-matrix step. A detailed analysis reveals a large variety of ground states at magnetization M equal to fractions 0,1/4, and 1/2 of the saturation magnetization M = 1. Some of these ground states break translational symmetry spontaneously and give rise to doubling of the unit cell. In a second part, we present complementary numerical data for the spin-1/2 Heisenberg model on the orthogonal-dimer chain. We analyze several examples of T = 0 magnetization curves, entropy as a function of temperature T and magnetic field, and the associated magnetic cooling rate. Comparison of the two models shows that in certain situations the simplified exactly solvable model yields a qualitatively or sometimes even quantitatively accurate description of the more challenging quantum model, including a case which may be relevant to experimental observations of an enhanced magnetocaloric effect in the two-dimensional compound SrCu_2(BO_3)_2.
机译：我们研究了在存在外部磁场的情况下，在正交二聚体链上具有三角形XXZ簇的spin / 1/2模型。首先，我们讨论三角形簇通过中间“经典”伊辛旋转耦合的情况。三角形XXZ簇的对角线化产生精确的基态。有限温度特性可以通过额外的传递矩阵步骤精确计算。详细的分析显示，磁化强度M等于饱和磁化强度M = 1的分数0、1 / 4和1/2时，存在多种基态，其中一些基态会自发地打破平移对称性，并导致倍频。晶胞。在第二部分中，我们在正交二聚体链上给出了自旋1/2 Heisenberg模型的补充数值数据。我们分析了T = 0磁化曲线，随温度T和磁场变化的熵以及相关的磁冷却速率的几个示例。两种模型的比较表明，在某些情况下，简化的可精确求解的模型对更具挑战性的量子模型产生了定性或有时甚至是定量的精确描述，包括可能与实验观察到的两种情况下磁热效应增强有关的情况。维化合物SrCu_2（BO_3）_2。

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