Development of highly sensitive magnetometer

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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.