In our Hall resistance measurement using PPMS DC resistance model with four probe method, we always encounter a problem that the resistance data randomly fluctuates, so we must remeasured a same sample many times and may have a relatively good data at some time, strongly influencing the efficiency and cost. I want to know, if this problem was a previous problem in many groups and what the reason is? The electrode? we connect the Pt wires on the film with Indium by hand pressing . if sputtering electrode metal on the film and then connecting the Pt wires would depress the problem? Thank you very much!
Good morning!
I have been a user of the PPMS for many, many years on different types of materials. I used almost all options available but mainly resistance (both DC and AC).
I would advise to first check what is the resistance of your contacts. My experience tells me that if the resistance is too high (say few kOhm), the data can fluctuate greatly. If so, I would try to make electrodes on the films, that should definitely help.
Are you sample very metallic? Keep in mind that the higher carrier concentration, the lower your signal will be, so it becomes very difficult when the samples are "too metallic". In case they are, I would advise to make as good contact as you can and use the AC option instead (good contact are required to minimise capacitive effect).
Last thing, you could take many times the same point and then make the average "manually". I did this in the past, as well as boosting the current, and it gave better measurements: you stop at the field you want to measure, and measure x times (like... 5) the resistance. Or maybe you can also increse the current?
I hope this helps!
Are the fluctuations occurring over the full temperature range of the instrument, or only at low temperatures? The indium contacts you are using may start to super conduct at about 3-4 K, which might explain the resistance fluctuations, but only near the base temperature.
Contact effects aside - as these have been discussed above. Hall effect is calculated by the difference between a number calculated with and without a magnetic field. If the two values are close together, because of low mobility for instance, you'll get a noisy reading. Using a large field permanent magnet (rather than an AC magnet) can help with this. Otherwise repeated measurements can be used to average out the noise. Eliminating electrical noise by using adequate shielding may also be important.
Thank you very much! we have confirmed the electrod is one important factor to introduce data fluctuation. we have try to change the indium electrod into siliver glue, which depresses the fluctuation much.
If you continue to have contact issues you might consider first putting down a bit of Au and then using a silver epoxy on top of that to attach the leads...
First you have to check the ground connection, the second have to make shielding and improve electrode contacts.
Hi all, I am trying to measure the Hall resistance of a ~5nm thin film using PPMS (I don't do the measurement myself) and I am a little confused about obtained results of the hall resistance vs. temperature which is negative values. Is there any explain on getting negative hall resistance values?
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