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，已被广泛关注。本文对Zr-N溅射薄膜进行了电学和声学测量。本研究取得的成果如下：1. Zr-N薄膜的分类：根据溅射条件、衬底温度和氮气分压等不同，可以将Zr-N薄膜进行分类，并根据电阻比分为两组。在室温和氦温之间。小磁电阻的起源：通过在高达30 T的磁场下的测量，研究了Zr-N薄膜的磁电阻。结果表明，Zr-N的磁电阻由量子干涉效应、自旋轨道效应和相互作用效应共同作用而成。弱场中的小磁电阻是由于这些贡献的偶然抵消而产生的。同时，也论证了铁磁性发生的可能性.电导率随温度变化的普适性：我们试图找到描述电导率随温度变化的普适函数。高温下大部分样品的电导率σ用σ = σ_0 +AAOT表示，低温下用σ = σ_0 +A（T-T_0）^<gamma>表示。找到了γ、A等之间的关系.新的弹性异常的发现：表面声波的速度显示出显着的异常作为温度的函数。具有高电阻比的强局域化样品在300 K以上显示出宽的最小值，并向低温软化。弱定域样品在15 K时只显示出一个宽的极小值.在二能级系统的基础上讨论了这些弹性反常现象及其与局域化的关系，从而对Zr-N薄膜的物理性质有了较为清晰的认识。这些结果将指导低温磁场温度计的研制。

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.