The Kondo Effect: Implications for Ferromagnetic Ordering and Beyond

[Dual Op Amp]

When a piece of steel goes through it's currie point, why wouldn't a current flowing through it drasticly change?

 

[Pieter Kuiper]

Do you mean the magnetic phase transition at the Curie temperature?
Why would you expect drastic changes? If you compare with the melting transition of metals, the change in resistivity is not enormous, and that is a first-order transition. At the phase transition at the Curie point is second order (the magnetization decreases contnuously to zero). Magnetoresistance and the anomalous Hall effect are affected, but the change in the ordinary resistivity is small.

 

[Dual Op Amp]

Thank you very much. I, actually, knew that. This is, simply, a post for my grandfather. He, for some reason, wondered why there is no drastic change in current flow after a piece of metal reaches it's currie point. I told him there was no reason for it to, but he insisted I post this to get a second opinion.

 

[ZapperZ]

Actually, we need to be a bit careful here. The resistivity of non-Fermi liquid material, for instance, can have a substantial effect on the ferromagnetic ordering, and thus, susceptible to the Curie temperature. This is due to what is known as the Kondo effect, where the conduction electrons have an antiferromagnetic coupling to the magnetic background. See, for example

http://www.physics.uc.edu/~jarrell/PAPERS/2CK_NFL_JPhys_CM_8_9825.pdf

An interesting feature of the Kondo effect is that the scattering strength grows as the temperature is lowered. The article mentions that

"...Kondo’s calculation actually foreshadowed the discovery of asymptotic freedom in quantum chromodynamics and has the same feature that systematic perturbation theory works well at high energy scales but fails at low energy scales."

This is another prime example of where the techniques coming out of many-body/condensed matter have wide-ranging implications in other areas of physics.

Zz.