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The traditional formalism for andreev reflection deals with what happens at normal metal, super conductor interface.http://en.wikipedia.org/wiki/Andreev_reflection (i.e when an electron from normal metal is incident on the super conductor interface, a hole is generated in the normal metal which lets the formation of a cooper pair in the SC which propagates in the appropriate direction)

How do we apply a similar formalism when an electron of say up-spin is incident from a normal metal to half-metal (magnet) ? what happens when this electron comes spin polarized at an angle to the interface ? note that unlike in superconductivity, there is a direction associated with the half metal (which is basically a magnet with an orientation)

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It seems you didn't read the wikipedia article too carefully, since there's a paper by de Jong and Beenakker in the references titled "Andreev Reflection in Ferromagnet-Superconductor Junctions". It even has a handy open-access arxiv link: arxiv.org/abs/cond-mat/9410014 –  wsc Jun 29 '11 at 5:25
    
I am looking for the FM-Normal metal junction. In any case, I will appreciate a clarification of the method they are using. –  New Horizon Jun 29 '11 at 5:29
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Oh, now I feel dumb because I didn't read your question too carefully ;) the whole phenomenon of Andreev reflection implies that one of the materials is a superconductor. –  wsc Jun 29 '11 at 5:33
    
There is no Andreev reflexion at the interface between a ferro and a normal metal. Andreev reflexion implies at least one superconductor. Or course there is nothing about your problem in a Wiki page about Andreev reflexion. Try looking for spin-torque effect instead, and tell me if you find something. Otherwise I'll give you the references. Have fun. –  FraSchelle Jun 25 '13 at 17:12
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There is no Andreev reflection in this case. You have to quantify the electron spin on the direction of the half-metal. The quantization direction is up to you, the electron does not decide.

If the electron is up, it will be transmitted with some probability depending on the precise band-structure matching. If it is down, it will be 100% reflected (assuming an ideal half-metal). If it happens to be at an angle, then you will just describe it as a quantum combination of up and down states, and you will get an angle-dependent transmission probability.

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