I am obtaining zinc ferrite samples by mechanical milling and then pressing the powders to apply a heat treatment. We are using 'Versalab' equipment to measure the electrical resistance by the four points method. The negative resistance was observed at 125 K.
Can you describe the 4-point geometry in more detail? And what are (i) the potential on the outer (source) leads to generate the current and (ii) the order of magnitude of the resistivity measured?
Why these questions? Well, I think you'll have to watch out for artifacts. Anything else would seemingly violate basic physical principles. And since you have reported this for manganite, too (see your post https://www.researchgate.net/post/I_got_negative_resistance_in_Magnetite_samples_can_someone_explain_the_possible_origin_of_this_behavior), stakes are high that there's some systematic issue with your set-up.
What could I suspect: you might have fairly high resistance and complex current paths in a pressed powder sample. Potentials then might effectively revert at the location(s) of your "inner" (probe) contacts.
With the manganite sample: did you see the effect of the Verwey transition (123K) in transport? (I would guess there should be some)
Some days back I have heard a talk where also apparent negative resistances occurred. It was clearly a "network effect" as I suspected above. The specimens were made up by interconnected nanowires at a surface. The behavior could be modelled through some network analysis and the apparent negative resistance understood.
Dear Prof. Fauth, I really appreciate your comments about my question. Following your comments we reviewed our measurements, and we found that the negative values were because someting wrong with the measurement array. Thanks a lot for your kindly help.
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