Development of highly sensitive magnetometer

本研究的目的是研制一种在<-8>2K ~ 1100 K温度范围内，在16 kOe的负、正磁场下，能探测到10 μ emu的磁矩的磁力计。磁力仪的工作原理如下：一对磁场梯度线圈固定在磁体的极片上。样品被大小可变的静态场磁化。当梯度线圈在磁性样品上产生交变磁场时，与样品的磁矩和场梯度的大小的强度成比例的交变力施加在样品上。固定在板簧上的样品杆在由弹簧常数和交变磁场的机械共振频率确定的机械共振频率下作共振，从而导致振动的增强。振动的幅度通过探测线圈检测，然后转换成与磁矩成比例的感应电压信号。通过使用锁定放大器检测电压。这种新型的磁力仪被称为共振样品磁力仪（RSM）。在RSM中还安装了一台气流式液氦低温恒温器和一台无感加热炉，获得了5 ~ 1000 K的温度范围。1998年3月现阶段，磁强计的性能如下：灵敏度：3.5 × 10&lt;@D1-7@&gt;D1 emu，温度范围：5 K ~ 1000 K，磁场范围：0-（]SY.+-. [)16现在对磁强计进行进一步改进，以实现10 μ emu量级的高灵敏度<-8>。日本Ltd.in荣株式会社将于1999年将商用型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.