Synchrotron X-ray Magnetic Scattering Studies under Strong Magnetic Fields

在这个项目中，我们的目标是用同步加速器X射线衍射技术来阐明量子磁系统在强磁场下的磁性和结构变化。(1)我们发现CuGeO_3在高场相CuGeO_3的不可公度性与临界场(〓12T)附近的温度有很大关系，而在足够高的场中，CuGeO_3的不可公度与温度无关。我们解释说，这一发现是由于抑制热涨落的强磁场稳定了无公度态。(2)在自旋1/2阶梯化合物Cu2(C_5H_&lt；12&gt；N_2)_2Cl4从自旋液体到长程有序相的临界场，人们预计会发生广义的自旋-Peierls相变，其中可能发生晶格扭曲。我们在世界最低温度0.04K和高场下对该化合物的单晶进行了X射线衍射研究。我们发现晶格常数沿a轴方向在临界场呈现不连续的变化。(3)尽管载流子浓度很小，但对致密近藤系统的典型样品CEP进行了同步加速器X射线衍射测量。在CEP中，两层类Γ_8 Ce和一层类Γ_7 Ce具有随外加磁场变化的周期。在高达14T的高场研究中，我们发现了具有8个周期和9个周期的新相。(4)我们成功地研制了用于同步辐射X射线衍射的脉冲高场。我们研制了一台无破坏产生高达35T脉冲场的分裂对磁体，并对一些化合物进行了X射线衍射测量。

In this project, we aim at clarifying the magnetic and structural changes in quantum magnetic systems under high magnetic fields using synchrotron X-ray diffraction technique. Some of the outstanding findings obtained from this project are briefly described below.(1)We have found that the incommensurability in the high field phase of a spin-Peierls compound, CuGeO_3 depends much on temperature near the critical field (〓12 T), while at high enough field it is independent of temperature. We have interpreted that this finding is due to a stabilization of the incommensurate state by a strong magnetic field which suppresses thermal fluctuations.(2)At the critical field from the spin liquid to a long-range ordered phase of a spin 1/2 ladder compound Cu_2(C_5H_<12>N_2)_2Cl_4,one expects a generalized spin-Peierls transition, in which a lattice distortion is predicted to occur. We have performed X-ray diffraction study on a single crystal of this compound at the World's lowest temperature of 0.04 K and at high fields. We have found that the lattice constant along the a-axis shows a discontinuous change at the critical field.(3)Synchrotron X-ray diffraction measurements have been performed on CeP which is a typical example of dense Kondo systems despite its small carrier concentration. In CeP two layers of Γ_8 like Ce and a layer of Γ_7 like Ce are stacked with a period which changes with an applied magnetic field. From our study performed in high fields up to 14 T we have discovered new phases with 8 and 9 periods.(4)We are successful in developing a pulsed high field for synchrotron X-ray diffraction. We have constructed a split pair magnet capable of producing pulsed field up to 35 T without destruction and measured X-ray diffraction on some compounds.