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arXiv 0902.0676cond-mat.str-el
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阻挫易轴三角形反铁磁体2 H- AgNiO2自旋动力学的中子非弹性散射研究

Spin dynamics of frustrated easy-axis triangular antiferromagnet 2H-AgNiO2 explored by inelastic neutron scattering

E. M. Wheeler, R. Coldea, E. Wawrzynska, T. Sorgel, M. Jansen, M. M. Koza, J. Taylor, P. Adroguer, N. Shannon

摘要:

我们报告的非弹性中子散射测量的自旋动力学的层状六角磁体2 H-AgNiO 2,其中堆叠的三角形层的反铁磁耦合Ni 2+自旋(S=1)有序的共线交替条纹图案。我们观察到一个宽频带的磁激发以上的小间隙为1.8毫电子伏,并延伸到7.5毫电子伏,表明强烈的色散激发。测得的粉末平均光谱的边界的色散可以定量地解释由反铁磁最近和弱次近邻耦合,强易轴各向异性和附加的弱层间耦合的三角形层的线性自旋波色散。由此产生的色散关系具有全球性的最小值,而不是在磁布拉格波矢,但在磁相关的软点,我们把这种异常的功能之间的强竞争的易轴各向异性和受挫的反铁磁耦合。我们还通过扩展Chubukov和Jolicoeur [Phys. Rev. B v46,11137(1992)]的工作,计算了自旋波理论中1/S阶色散关系的量子修正,发现易轴各向异性的存在显著降低了各向同性模型预测的量子重整化。

英文摘要:

We report inelastic neutron scattering measurements of the spin dynamics in the layered hexagonal magnet 2H-AgNiO2 which has stacked triangular layers of antiferromagnetically-coupled Ni2+ spins (S=1) ordered in a collinear alternating stripe pattern. We observe a broad band of magnetic excitations above a small gap of 1.8 meV and extending up to 7.5 meV, indicating strongly dispersive excitations. The measured dispersions of the boundaries of the powder-averaged spectrum can be quantitatively explained by a linear spin-wave dispersion for triangular layers with antiferromagnetic nearest- and weak next-nearest neighbor couplings, a strong easy-axis anisotropy and additional weak inter-layer couplings. The resulting dispersion relation has global minima not at magnetic Bragg wavevectors but at symmetry-related soft points and we attribute this anomalous feature to the strong competition between the easy-axis anisotropy and the frustrated antiferromagnetic couplings. We have also calculated the quantum corrections to the dispersion relation to order 1/S in spin-wave theory by extending the work of Chubukov and Jolicoeur [Phys. Rev. B v46, 11137 (1992)] and find that the presence of easy-axis anisotropy significantly reduces the quantum renormalizations predicted for the isotropic model.

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