Test and qualification of a variable temperature vibrating sample magnetometer system for the measurement of magnetization cycles up to +/-12T in the 4.2K-300K temperature range

摘要

A complete characterisation of an Oxford Instruments Vibrating Sample Magnetometer (VSM) has been made in order to check the limits and the reproducibility of the system as well as the measurement accuracy. Several measurement cycles have then been carried out to check the extent of the difference between the actual sample temperature and the sensor reading, and the weight of this difference on the magnetization data as a function of the temperature. Moreover an unexpected lowering of a reference signal has been observed at low temperatures, most probably due to shielding currents in the structure; this effect influences the sample signals, and has to be taken into account during data analysis. Being the magnetization a relative measurement, a great attention must be paid to the calibration procedure. Calibrations with 99.999% pure Nickel and Palladium, which have magnetization signals two order of magnitude apart, give comparable calibration constants. We observed that in order to have high accuracy measurements, the calibration has to be performed on samples geometrically identical to the test ones, and periodically repeated. The repeatability of the measurement has been found to be +/-1%; once corrected the image current effect, the accuracy of the measurements, at 4.2 K, is +/-3%. This value was also confirmed by the direct comparison of our results with those obtained at National Institute of Standards and Technology (NIST) on the same Nb3Sn samples. [References: 1]