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，稀土元素的超导电性和磁有序性是共存（或竞争）的，其中超导电性、磁性和晶格动力学是密切相关的。当RE = Ho时，超导转变温度（Tc = 7K）与磁转变温度（T_N = 5K）接近，超导和磁性的温度-磁场相图复杂，包含了重入超导相和反铁磁、铁磁、亚铁磁和无公度磁相。本文用超声波测量和单轴应力作用下的晶格形变来研究HoNi_2B_2C的超导电性和磁性之间的关系。我们仔细地检验了用区熔法制备的单晶的超导电性与样品的关系，发现在超导电性的研究中，常常出现多个超导相，它们的超导性与样品的磁性质有关。在超导电性的研究中，我们发现，在超导电性的研究中，超导相的数目和超导相的数目是多个的。在超导电性的研究中，超导相的数目和超导相的数目是多个的。在超导电性的研究中，超导相的数目和超导相的数目是多个的，超导相的数目和超导相的数目是多个的，超导相的数目和超导相的数目是多个的，超导相的数目和超导相的数目是多个的，超导相的数目和超导相的数目是多个，超导相的数目和超导相的数目是多个，超导相的数目和超导相的数目是多个，超导相的数目和超导相的数目是 关于我们 超声波测量表明，与应变相关的弹性常数C_（沿着[110]）随温度从80 K降低到T_N而出现大的软化，软化程度可达60%。<66>我们的结论是应变耦合与铁磁波动的Ho磁矩内的c-平面。与应变沿着[001]相关的弹性常数C_随温度从80 K降低到T_N也表现出类似的软化，但其变化比C_小两个数量级。<33><66>此外，在2K时，C_（1-x）表现出与亚磁性转变相关的阶梯软化。<33>我们得出结论，应变沿着[001]耦合与磁相关的Ho磁矩之间的c-平面。在单轴应力下的磁性测量表明，T_N随应力沿着方向的增加而显著增加[110]。该速率比水压下的速率大1个数量级。另一方面，在本精度范围内，T_N不随[001]方向沿着的应力而变化。除了上述研究外，我们还在Spring-8进行了初步的同步辐射X射线磁散射实验。我们证实了周期性的反铁磁和铁磁相在2K的磁布拉格散射。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