We use a HMS 3000 Version 3.51.5 machine for Hall Effect measurement in our lab. Why does it show positive and negative Hall Coefficient randomly in different for the same sample at the same temperature? The other conditions, viz. magnetic field, electric current, measurement number are kept same all readings.
Thank you
Munira
Connections might be loose. How much is the Hall voltage & what is its noise?
If it is ~ noise, then random sign change is not ruled out.
Munira has to answer: How much is the Hall voltage & what is its noise?
Thank you, professor Alak KUMAR Majumdar. I really appreciate your suggestion. I double checked the connection and it seems everything is okay. Hall voltage was about 20 mv.
Suppose, I did hall measurement of a sample at same condition for five times, it gave me positive hall coefficient for three times and negative hall coefficient for two times. The value is in the same order, but the polarity changes randomly.
HMS 3000 uses Van der Pauw Method. I couldn’t find any information regarding noise in machine specification or data. Hence, I’m not sure about the noise. Is there any way to check the noise?
The official site of ecopia says about HMS 3000 in verbatim “Minimizing an allowable error with setting the 6 stage of current ranges to constant input current (1nA ~ 20mA) and also minimizing of electrical noise by using Van der Pauw technique method “. Corresponding link is
http://www.ecopia21.co.kr/bbs/board.php?bo_table=eng_product&wr_id=21
Some ideas:
1. Is the measured voltage an artefact? Is noise or EM interference being rectified to produce a DC artefact? Could there be a junction e.g. mal-formed ohmic contact to sample. Try screening the leads.
2. Could the voltage be some kind of thermoelectric effect? Could the leads of contacts be contaminated? 20mV seems a lot for this.
3. If you are measuring a true Hall voltage, then positive and negative voltages could be generated in same sample if this is a semiconductor and the doping is non-uniform and there are both donor and acceptor impurities. What material is your sample? Has it been doped?
4. Have you tried making the same measurement on another sample from the same batch of material? Do you get the same result.
Regards,
Jonathan
Did you take 4 sets of data for a given magnetic field?
+ B, + I + B, - I - B, + I - B, - I ???
Yes, our machine takes automatically 4 sets of data.
Thank you so much for your help. I am going to take the hall measurement again for some newly deposited samples, taking your ideas in consideration. I would probably have more questions on this issue.
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