Development of highly sensitive magnetometer

本研究的目的是研制一种磁力计，可以在2K ~ 1100K的温度范围内，在16 kOe的负、正磁场下，探测到10^<-8> emu的小磁矩。磁力计的工作原理如下：在磁体的极片上固定一对磁场梯度线圈。样品被大小不等的静磁场磁化。当梯度线圈在磁性试样上产生交变磁场时，在试样上施加的交变力与试样的磁矩和磁场梯度的大小成正比。固定在板弹簧上的试样杆，在由弹簧常数和交变磁场常数确定的机械共振频率下，产生共感振动，使振动增强。通过搜索线圈检测振动的振幅，然后将其转换为与磁矩成比例的感应电压信号。电压是用一个锁相放大器检测的。这种新型磁强计称为谐振样品磁强计（RSM）。在RSM中还安装了气流式液氦低温恒温器和带无感加热器的炉膛，获得了5K ~ 1000K的温度范围。在1998年3月的现阶段，磁力计的性能如下：灵敏度：3.5*10<@D1-7@>D1鸸鹋，温度范围：5K-1000K，磁场范围：0-(]SY.+-。() 16 kOe。目前正在对磁强计进行进一步改进，以实现10 ^<-8> emu数量级的高灵敏度。日本东映株式会社将于1999年将商用基地RSM投放市场。

The purpose of this study is to develop and to construct the magnetometer which can detect the magnetic moment so small as 10^<-8> emu over the temperature range from 2K to 1100K under magnetic fields up to 16 kOe in a negative and positive sense. The operational principle of the magnetometer is as follows ; A pair of field gradient coil is fixed on the pole piece of a magnet. A sample is magnetized by static fields variable in magnitude. When the gradient coil generates an alternating magnetic field on the magnetic specimen, an alternating force, proportional to both the magnetic moment of the sample and the strength of the magnitude of the field gradient, exerts on the sample. The sample rod fixed on a plate spring vibrates sympathetically at the mechanical resonance frequency determined by the spring constant and that of the alternating magnetic field, resulting the enhancement of the vibration. The amplitude of the vibration is detected by means of a search coil and, then, is converted to the inductive voltage signal proportional to the magnetic moment. The voltage is detected by using a lock-in amplifier. This new type magnetometer is call as Resonating Sample Magnetometer (RSM). A gas flow type cryostat of liquid He and a furnace with non-inductive heater are also installed in the RSM,and the temperature range from 5K to 1000K is obtained.At the present stage of March 1998, the performance of the magnetometer is as follows ; The sensitivity : 3.5*10<@D1-7@>D1 emu, the temperature range : 5K-1000K,and the magnetic field range : 0-(]SY.+-。[)16 kOe.The further improvement of the magnetometer is now carried out so as to realize the high sensitivity of the order of l0^<-8> emu. TOEI Co. Ltd.in Japan will put the commercial base RSM on the market in 1999.