Study on Quantum Phase Transition of Magnetic Materials induced by Very High Field

在本研究中，我们开发了一种磁性系统，可以像通常的方法一样进行高达70 T的磁化测量，并成功地观察到极高磁场引起的各种量子现象。例如，我们成功地在BlP-TENO中观测到了整个/4平台，并将其视为S=1反铁磁自旋梯材料。由于该材料的磁性来自自由基，自旋应为1/2，但自旋之间存在较大的铁磁相互作用，使两个自旋产生自旋为1。从晶体结构分析来看，自旋1形成自旋阶梯，从低场磁场测量中发现自旋1之间的相互作用是反铁磁性的。到目前为止，高磁场测量表明，1/4平台在44 T左右开始，但该体系存在1/4平台并不明显。在我们的研究中，通过将磁化测量扩展到70 T，首次观察到1/4高原的末端，这也使我们能够看到整个高原区域，从44 T左右开始到65 T左右结束。另一个引人注目的例子是S=1。近年来，人们已经清楚地认识到，当分子被吸附到某些铜复合材料的微孔中时，其磁性以与反铁磁有序不同的方式消失。我们利用强磁场成功地观察到了非磁性态向磁性态的转变。有趣的是，虽然S=1分子在材料中形成自旋阶梯，但没有平台。

We have developed in this study the magnet system to carry out the magnetization measurement up to 70 T as a usual manner and succeeded in observing various quantum phenomena induced by very high magnetic field. For example, we have succeeded in observation of wholel/4 plateau in BlP-TENO, which has been regarded as an S=1 antiferromagnetic spin ladder material. As the magnetism of this material comes from free radical, spin should be 1/2 but there is large ferromagnetic interaction between the spins that makes two spins resulted spin 1. From a crystal structure analysis, spin 1 form a spin ladder and the interaction between spin 1 is found to be antiferromagnetic from the magnetic measurements at low field. Up to now, high field magnetization measurement has showed that 1/4 plateau begins around 44 T but it is not obvious that the 1/4 plateau exists in this system. The end of 1/4 plateau has been observed for the first time in our study by extending the magnetization measurement up to 70 T and it also allow us to see the whole plateau region, which begins around 44 T and ends around 65 T. Another striking example is a of S=1. Recently, it has become clear that magnetism of the molecule disappears in a different manner as the antiferromagnetic ordering when it is adsorbed into micro-pores of some copper complex materials. We have succeeded in observation of transition from non-magnetic state to magnetic one by applying high field. It is also interesting point that there is no plateau though the S=1 molecules form spin ladder in the materials.