Speaker
Description
Vibrating sample magnetometry (VSM) is a powerful technique for investigations of magnetic properties of matters. One important drawback of this technique is the ‘open-loop’ setup which can significantly distort the exact magnetic properties. Thus, appropriate corrections especially in the strong ferromagnet such as permanent magnets is required. In this work, we design the systematic experiments by varying the length/radii ratio between 1-5 and provide the step-by-step corrections of two commercial NdFeB powder magnets with reported energy product ((BH)max) of 6 ± 0.5 and 12.7 ± 0.5 MGOe. It is seen that the raw VSM hysteresis loops contain the paramagnetic-like slope and unsaturated curve which directly pervert their magnetic properties. These effects could be experienced from the equipment calibrations, powder samples and ‘open-loop’ setup. These hysteresis loops give the calculated (BH)max of 47.3 – 62.6% compared to their reported values with improper values of saturation magnetization (Ms), remnant magnetization (Mr) and Mr/Ms ratio. In order to correct the measured VSM hysteresis loop, firstly, the paramagnetic-like slope of 0.0500 – 0.0735 was subtracted until the flat at high fields was obtained. Secondly, the Ms ratio within ±5% was added to achieve the same Ms for all samples. Finally, the demagnetizing field correction (N) of 0.29287 – 0.43804 depending on their geometry was applied to all samples. The corrected (BH)max after all processes is around 86-95% of the reported values. Moreover, the samples with different packing densities were also examined. The results show that the loose packed sample exhibits hysteresis distortion which could be caused by an unwanted magnetostatic interaction and degree of particle rotation of the powder. This work demonstrates the importance in preparing and interpreting the VSM results and might be a facile way to get credible magnetic performance without performing magnetic alignment of such permanent magnets.
