Precise Measurements of the Low-Field Hall Coefficient and Magnetoresistance in Metals

在本研究中，对超导斩波放大器进行了改进。首先，锁相放大器参考信号的外部输入通过光纤连接到操作超导斩波器的脉冲发生器。减小了感应噪声的影响，使放大器在噪声条件下能以5 <p^V>的灵敏度工作。接下来，将4（1/2）位的数字万用表替换为5（1/2）位的数字万用表，作为记录样品电流和参考电流的仪器。通过这种方式，在各种测量中可以获得5 <p^V>的全灵敏度。在4.2 K温度下，对高纯度铝单晶试样进行了低场霍尔系数和磁阻系数的精确测量。含三维金属元素的稀铝合金的多晶试样。作为溶质元素，Sc、Ti和Cu在10-1000 at。使用PPM。迄今为止，据报道，这种合金的低场霍尔系数与溶质元素的原子序数呈抛物线关系。抛物线的中心在Cr。但是，在本研究中发现，霍尔系数从Sc到Cu单调增加。此外，Al-100 at的霍尔系数和磁阻系数在低场极限处出现了异常。ppm Ti和Al-1000 at。ppm钛合金。霍尔系数比自由电子值（-3.41x <10^(-11)> <m^3> /C）更负，磁阻系数比其他合金体系大得多。需要对实验和理论进行更详细的研究。

In the present investigation, a superconducting chopper amplifier has been improved. First, the external input for the reference signal of a lock-in amplifier was connected through a photo-fibre to a pulse generator which operates the superconductiong chopper. The influence of inductive noises was reduced to the extent that the amplifier could operate with a sensitivity of 5 <p^V> under noisy conditions. Next, a digital multimeter of 4(1/2) digits was replaced by that of 5(1/2) digits as a recording instrument for a specimen current and a reference current. In this way, a full sensitivity of 5 <p^V> became available in various measurements.Precise measurements of the low-field Hall and magnetoresistance coefficients were performed at 4.2 K on a monocrystalline specimen of high-purity aluminium with quenched-in vacancies of a few at.ppm, and on polycrystalline specimens of dilute aluminium alloys with 3d metal elements. As solute elements, Sc, Ti and Cu of 10-1000 at.ppm were used. Hitherto, it has been reported that the low-field Hall coefficients of such alloys are parabolic with respect to the atomic number of solute elements. The centre of the parabola is at Cr. But, in the present investigation, it has been found that the Hall coefficients increase monotonically from Sc to Cu. Moreover, anomalies of the Hall and magnetoresistance coefficients in the low-field limit have been found in Al-100 at.ppm Ti and Al-1000 at.ppm Ti alloys. The Hall coefficient became more negative than the free-electron value of -3.41x <10^(-11)> <m^3> /C, and the magnetoresistance coefficient became much larger than that in other alloy systems. More detailed investigations will be desired both on experiments and theories.