Measurement of Resistivity of NdFeB Magnet with Four-probe Method
Roughness,thickness,area dimension,temperature,etc are relevant factors for the measurement of resistivity of NdFeB permanent magnet.The appropriate setting of the above conditions is necessary to ensure the accuracy of resistivity measurement.Without UPS power supply,the deviation between the highest and lowest value of the resistivity measurement is 5％,while the UPS power supply is added,the deviation of the resistivity measurement is 1.2％,which is significantly re-duced.When the roughness of NdFeB sample is only 0.39 µm,the measured value of resistivity is 139.84 μΩ·cm,and when the roughness is 7.79 μm,the measured value of resistivity is 147.20 μΩ·cm.As sample becomes thicker,the resis-tivity increases.When the thickness is in the range of 1 mm～5 mm,the measured resistivity rises rapidly with the increase in thickness;after the thickness exceeds 5 mm,the resistivity exhibits fluctuations in a small platform.For a probe interval of 1 mm,samples with an area of 20 mm×20 mm or more can meet the measurement requirements.It can be known from the resis-tivity experiment related to thickness and area that the larger the sample size,the better the accuracy of the measurement.As the temperature increases,the resistivity of the sample has a tendency to increase.But for M,H,SH brand samples,the re-sistivity at 200 ℃ is less than 170 ℃;for UH brand sample,the peak value of resistivity appears at 110 ℃.
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