Spin gap in the Quasi-One-Dimensional S=1/2 Antiferromagnet: Cu2(1,4-diazacycloheptane)2Cl4
Spin gap in the Quasi-One-Dimensional S=1/2 Antiferromagnet: Cu2(1,4-diazacycloheptane)2Cl4
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准一维 S=1/2 反铁磁体中的自旋间隙：Cu2(1,4-二氮杂环庚烷)2Cl4
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发表时间：
1997
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通讯作者：
Il
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作者：
P. R. Hammar;D. Reich;C. Broholm;F. University;Baltimore.;MD National Institute of Standards;Technology;Gaithersburg;MD Ipns;Argonne National Labs;Argonne;Il
Cu_{2}（1，4-二氮杂环庚烷）_{2}Cl_{4}含有自旋为1/2的Cu^{2+}离子双链。我们报告交流磁化率，比热，和非弹性中子散射测量这种材料。的磁化率，$chi（T）$，在T = 8 K表示低维反铁磁体没有零场磁相变的四舍五入的最大值。我们比较了$chi（T）$数据与各种一维自旋哈密顿量的精确对角化结果，发现对于自旋梯，其内部能级耦合为$J_1 = 1.143（3）$ meV，两个相互阻碍的能级间相互作用为$J_2 = 0.21（3）$ meV和$J_3 = 0.09（5）$ meV。零场比热是指数激活的，激活能δ = 0.89（1）$ meV。通过粉末样品上的非弹性中子散射也发现了自旋间隙，其确定了$0.8 < hbaromega < 1.5$ meV的磁激发带。使用求和规则，我们推导出与非相互作用的传播在一个自旋梯的三重态的动态自旋相关函数的表达式。在我们的散射数据中没有观察到这种模型的van-Hove奇异性，表明Cu_{2}（1，4-二氮杂环庚烷）_{2}Cl_{4}中的磁激发更为复杂。当磁场强度高于$H_{c1} simeq 7.2$ T时，比热随温度的变化显示出反常现象，表明在T = 1 K以下的温度下，相变为有序态。
Cu_{2}(1,4-diazacycloheptane)_{2}Cl_{4} contains double chains of spin 1/2 Cu^{2+} ions. We report ac susceptibility, specific heat, and inelastic neutron scattering measurements on this material. The magnetic susceptibility, $chi(T)$, shows a rounded maximum at T = 8 K indicative of a low dimensional antiferromagnet with no zero field magnetic phase transition. We compare the $chi(T)$ data to exact diagonalization results for various one dimensional spin Hamiltonians and find excellent agreement for a spin ladder with intra-rung coupling $J_1 = 1.143(3)$ meV and two mutually frustrating inter-rung interactions: $J_2 = 0.21(3)$ meV and $J_3 = 0.09(5)$ meV. The specific heat in zero field is exponentially activated with an activation energy $Delta = 0.89(1)$ meV. A spin gap is also found through inelastic neutron scattering on powder samples which identify a band of magnetic excitations for $0.8 < hbaromega < 1.5$ meV. Using sum-rules we derive an expression for the dynamic spin correlation function associated with non-interacting propagating triplets in a spin ladder. The van-Hove singularities of such a model are not observed in our scattering data indicating that magnetic excitations in Cu_{2}(1,4-diazacycloheptane)_{2}Cl_{4} are more complicated. For magnetic fields above $H_{c1} simeq 7.2$ T specific heat data versus temperature show anomalies indicating a phase transition to an ordered state below T = 1 K.