The electrons in the illustration are represented by small magnets as it is their magnetic qualities that give rise to giant magnetoresistance. The magnetic moment in the electrons is the result of their internal "rotation", spin, that can point upwards or downwards. Here the electric current is divided into one part that consists of spin-up electrons and one consisting of spin-down electrons. The increased resistance in the magnetic material for electrons with the "wrong" spin is represented in the illustration as a hole pointing in the wrong direction that makes it impossible for the electrons to get through. |
Magnetism and resistance at nano-level
Giant magnetoresistance arises when a non-magnetic material is sandwiched between thin layers of a magnetic metal. The effect derives from the internal "rotation" of the electron, its spin, which creates a magnetic moment. Each electron behaves like a small magnet, pointing either upwards or downwards. Giant magnetoresistance depends on the difference in electrical resistance for electrons with different spin directions in thin magnetic layers.
A sandwich of nanometre thick magnetic layers with a non-magnetic layer in the middle will allow different magnitudes of current to pass through it depending on whether the magnetization in the magnetic layers points in the same direction (the upper figure) or is opposed (the lower figure). In the first case the electrons with the "correct" spin pass straight through the sandwich and an electric current therefore flows through the structure even though electrons with the "wrong" spin are dispersed in the first layer. In the second case, where the magnetization is opposed, all the electrons are "wrong" in one of the two magnetic layers so that the total resistance is large and bars the flow of electric current. |
