A new paper appearing in Science today is reporting the properties of a molecular wire that has the capability of having a 2000% increase in its magnetoresistance, and all at room temperature!
Ironically, the new molecular wires aren't made with magnetic materials at all. Rather, their MR effect relies on the conductivity of nonmagnetic organic dye molecules called DXP, which the Italian automaker Ferrari once used to give their roadsters their trademark red color. Unlike conventional inorganic metals in which electrons zip through a crystalline lattice, in organics electrons must hop from one molecule to another, like pails of water being passed by a bucket brigade. To create a MR, material researchers need to switch off that bucket brigade in the presence of a magnetic field.Of course, we all know (don't we?) that this is the field that has been responsible for invention of computer magnetic storage disks, etc. So kids, this is another example of real-world, practical application of physics, and quantum mechanics in particular.
In organic materials researchers do this with a little help from quantum mechanics. A tenet of quantum mechanics called the Pauli Exclusion Principle states that no two fermions (particles in a family that includes electrons) can occupy the same quantum state. If two electrons with the same quantum state try to hop onto the same DXP, they can't. The bucket brigade turns off and resistance skyrockets.