AC susceptibility setup for 7K closed cycle refrigerator

Abstract

Cryocooler based ac susceptometer is designed. Ac susceptibility is measured using the mutual inductance principle. The setup made of hylum consists of primary coil, secondary coil and a sample holder. Copper wire (150micron) winding is done on the primary and the secondary coils. The secondary coil is connected in series opposition i.e. if one wound is clockwise, the other is anticlockwise. Lock-in amplifier excite the primary coil, and the signal from secondary is given to the lock-in-amplifier itself where the in-phase and out-phase components are separated. Lakeshore Temperature controller is used for the detection of cryocooler temperature and a Pt100 temperature sensor is used for the detection of sample temperature. This is because as the distance between the cryocooler and the sample is more, so cryocooler temperature sensor is not able to detect the sample temperature. The temperature controller and lock-in-amplifier is then interfaced with computer using Lab-View program. Then, LSMO sample is prepared for testing the working of set up. Sample is prepared by auto combustion sol-gel method. Pellets are made which is cut into rectangular shape and placed in the centre of one of the secondary coil. Then the ac susceptibility measurement is done by keeping the frequency constant (834 Hz) in lock-in amplifier. Data are plotted and the susceptibility plot with sample is obtained. The susceptibility plot for sample was obtained by deducting the background from the susceptibility plot with sample. The phase change in the LSMO system is studied using the Ac susceptometer.