Lattice anomaly associaterd with the magnetic order in a re-entrant superconductor Ho_<1-x>Y_xNi_2B_2C

在RNi_2B_2C（R=稀土元素）中，稀土元素的超导性和磁序共存（或竞争），其中超导性、磁性和晶格动力学三者密切相关。RE =Ho时，超导转变温度（Tc=7K）接近磁转变温度（T_N=5K），超导和磁的温度-磁场相图较为复杂，包括可重入超导相和反铁相、铁相、铁相和不适应磁相。本项目的目的是通过超声测量和单轴应力下的晶格变形，通过“晶格”来阐明HoNi_2B_2C的超导性与磁性之间的相互关系。我们仔细地检查了由焙烧区红外炉制备的单晶的超导性的样品依赖性，发现即使在单晶中也存在多个超导相。超声测量结果表明，当温度从80 K降至T_N时，与[110]沿线应变相关的弹性常数C_<66>出现了较大的软化，软化幅度可达60%。我们得出了应变与c平面内Ho磁矩的铁磁波动耦合的结论。与[001]沿线应变相关的弹性常数C_<33>随温度从80 K到T_N的降低表现出类似的软化，但其变化比C_<66>小两个数量级。此外，C_<33>在2 K处表现出与亚磁跃迁相关的逐步软化。我们得出结论，沿[001]的应变与c-面之间的Ho磁矩磁相关耦合。我们推导了c-平面间交换相互作用对c-间距的依赖关系。单轴应力下的磁测量表明，沿应力方向施加应力，T_N显著增加[110]。该速率比水压下的速率大1个数量级。另一方面，在当前精度范围内，T_N不随应力沿[001]方向变化。我们没有发现在各个方向上应力对Tc有任何明显的变化。在此基础上，我们利用同步辐射在Spring-8上进行了初步的x射线磁散射实验。我们用磁布拉格散射证实了反铁磁相和铁磁相在2k时的周期性。少

In RNi_2B_2C(R=rare earth elements) the superconductivity and the magnetic order of the rare-earth elements coexist, (or compete), where the superconductivity, the magnetism, and the lattice dynamics are closely related to the others. When RE =Ho, the superconducting transition temperature (Tc=7K) is close to the magnetic transition temperature (T_N=5K), and the temperature vs magnetic-field phase diagram for the superconductivity and the magnetism is complicated involving the reentrant superconducting phase and antiferro-, ferri-, ferro-, and incommensurate magnetic phases. The purpose of the present project is to elucidate the interrelation between the superconductivity and the magnetism of HoNi_2B_2C through "lattice" by the ultrasonic measurement and by lattice deformation under uniaxial stresses.We carefully checked the sample dependence of the superconductivity of the single crystals prepared by a froating-zone infraned furnace, and found that multiple superconducting phases ofte … More n coexist even in a single crystal.The Ultrasonic measurements revealed that the elastic constant C_<66>, relevant to the strain along [110], shows a large softening up to 60% with decreasing temperature from 80 K to T_N. We conclude that the strain couples with the ferromagnetic fluctuation of Ho magnetic moments within the c-plane. The elastic constant C_<33>, relevant to the strain along [001], shows a similar softening with decreasing temperature from 80 K to T_N although its change is smaller by two orders of magnitude than C_<66>. In addition, C_<33> shows stepwise softenings associated with the meta-magnetic transitions at 2 K. We conclude that the strain along [001] couples with the magnetic correlation of Ho magnetic moments between the c-planes. We deduced the dependence on the c-spacing of the exchange interactions between the c-planes.The magnetic measurements under uniaxial stress revealed that T_N increases remarkably by applying a stress along [110]. The rate is larger by 1 order of magnitude than that in the hydro-pressure. On the other hand, T_N dose not change by the stress along [001] within the present precision. We did not find any appreciable change of Tc by the stresses in all directions.In addition to the above investigation, we performed preliminary x-ray magnetic scattering experiment using synchrotron radiation in Spring-8. We confirmed the periodicity of the antiferro- and ferri- magnetic phases at 2 K by magnetic Bragg scattering. Less