Research on Development of Thermometers for Cryogenic Temperature in Magnetic fields

Zr-N溅射薄膜作为低温磁场温度计的最佳候选材料受到了广泛的关注，并通过电和声学测量对其进行了研究。本研究项目获得的结果总结如下：1。Zr-N薄膜的分类：不同溅射条件下制备的Zr-N薄膜；基材温度和氮气分压，可按电阻比分为两组。在室温和氦气温度之间。小磁阻的来源：通过对Zr-N薄膜的磁阻（MR）在高达30T的电场中的测量，研究了Zr-N薄膜的磁阻。发现Zr-N的MR由量子干涉、自旋轨道和相互作用效应的各种贡献组成。弱场中的小磁共振是由于这些贡献的偶然抵消而产生的。提出了铁磁性存在的可能性。电导率温度依赖的普遍行为：我们提出了寻找描述电导率温度依赖的普遍函数的尝试。在高温下，大部分样品的电导率为sigma=sigma_0+AAOT，在低温下为sigma=sigma_0+A(T-T_0)^<gamma>。得到了γ、A等之间的关系。新的弹性异常的发现：表面声波的速度随温度的变化表现出明显的异常。高电阻比的强局部化试样在300 K以上表现出宽的最小值，并向低温方向软化。弱局部化样品在15k时有一个宽的最小值。在二能级系统的基础上讨论了这些弹性异常及其与局部化的关系。通过一系列的研究，明确了Zr-N薄膜的物理性质。这些结果将导致在磁场低温下使用的温度计的成功开发。

Zr-N sputtered films, which have been drawn attention as the best candidate for the thermometers at cryogenic temperature with magnetic fields, have been investigated by electrical and acoustical measurements. The results obtained in this research project are summarized as below.1. Classification of Zr-N films : Zr-N films fabricated with various sputtering conditions ; substrate temperature and nitrogen partial pressure, can be classified and divided into two groups by the resistance ratio. between room and helium temperatures.2. Origin of small magnetoresistance : Magnetoresistance(MR)of Zr-N films is investigated by the measurements in the field up to 30T. It is found that MR of Zr-N consists of various contributions from quantum interference, spin-orbit and interaction effects. The small MR in weak field arises from accidental cancellation of these contributions. The possibility of occurrence of ferromagnetism was also suggested.3. Universal behavior in temperature dependence of electrical conductivity : We present attempts for finding the universal function which describes T dependence of conductivity. The conductivity sigma is described as sigma=sigma_0+AAOT for major parts of samples at high temperatures, and as sigma=sigma_0+A(T-T_0)^<gamma> at low temperatures. The relations among gamma, A, etc. are found.4. Discovery of novel elastic anomalies : The velocity of surface acoustic wave shows remarkable anomalies as a function of temperature. The strongly localized sample with high resistance ratio shows a broad minimum at above 300 K and a softening toward low temperature. The weakly localized sample shows sole a broad minimum at 15 K. These elastic anomalies and the relation to the localization are discussed based on two-level-system.From the series of investigations, the physical properties of Zr-N films has been made clear. These results would lead the successful development of then-nometers for the use at cryogenic temperature in magnetic field.