标题: 低维度磁性材料SrCo2V2O8的核磁共振研究
NMR Study of the Low-Dimensional Magnetism in SrCo2V2O8
作者: 陈韦儒
杨本立
电子物理系所
关键字: 核磁共振;准一维自旋链;NMR;Quasi-One-Dimensional Spin Chain
公开日期: 2009
摘要: 本论文主要是利用核磁共振(NMR)的技术来探讨准一维自旋链(spin-chain)材料SrCo2V2O8 中所出现的反铁磁相变。我们量测样品中V51的NMR讯号,观测其NMR频谱于不同温度及磁场下的变化。在固定磁场(B~26.8KG)下,磁场平行于晶格的c轴时,我们发现此样品在T=4K,开始从高温的顺磁态进入到低温的反铁磁态,但在T=3.85-3.9K,出现顺磁-反铁磁共存的态,然后又在T=3.3K~3.7K,出现spin-flop的相转变,最后才达到稳定的反铁磁态。从频谱的结构分析,我们认为此反铁磁态中,Co+2的磁矩排列为commensurate。另外,为了探讨样品中在磁场下所出现的metamagnetic相变,我们固定温度(T=2.5K),量测样品在不同磁场下的频谱,发现此metamagnetic相变主要是由于spin-flop transition所引起,而非单纯磁场所引发的顺磁-反铁磁相变。藉由本实验的结果并与其他类似的准一维自旋链材料做比较,将有助于更深入的瞭解自旋链材料的磁性。
The field of low-dimensional magnetism has received considerable attention in recent decades, as the theoretical modeling of interactions at low dimensions can be done easily, and novel phenomena often occur experimentally. This thesis reports a nuclear magnetic resonance (NMR) study of the quasi-one-dimensional antiferromagnetic (AFM) spin-chain system, SrCo2V2O8, including a detailed study of its magnetic phase diagram.
We measured the V51 NMR spectra at different temperatures and magnetic fields. For a fixed NMR field (~26.8kG) applied parallel to the c axis, the temperature-swept spectra show an onset of AFM transition at 4K, but there is a coexistence of paramagnetic and antiferromagnetic phases down to 3.9K. Following that is a spin-flop transition in the range of T=3.3-3.9K. The stable AFM state finally occurs below 3.3K. By analyzing the spectra, we found that the antiferromagnetic ordering of Co+2 moments is commensurate with the lattice.
We also investigated the field-induced metamagnetic transition by taking the V51 spectrum at several different fields across the phase boundary at 2.5K. We found that the metamagnetism is caused by the spin-flop transition, and not the paramagnetic-antiferromagnetic transition.
Our findings will also facilitate a better understanding of similar quasi-one-dimensional spin-chain systems such as PbCo2V2O8, as well as related theoretical studies.
URI: http://140.113.39.130/cdrfb3/record/nctu/#GT079721529
http://hdl.handle.net/11536/45015
显示于类别:Thesis


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