Ballistic magnetoresistance

(BMR) is yet another way in which spin orientation can modify electrical resistance in a circuit. The sensitive part of the circuit might consist of sandwiches of alternating magnetic and nonmagnetic layers (giant magnetoresistance and tunnel magnetoresistance) or might have no magnetic materials at all (extraordinary magnetoresistance; see Physics Today, Physics Today 0031-9228 55 7 2002 9  https://doi.org/10.1063/1.2409334 July 2002, page 9 ). In BMR, the sensor is a quantum point contact of ferromagnetic atoms between two wires. The contact is narrower than the typical scattering path length for electrons, which therefore move ballistically in straight trajectories. Any scattering an electron suffers will be due only to magnetic effects. If the electrons in the circuit are spin polarized then they will scatter more or less (with greater or lesser resistance) at the contact, depending on the contact’s magnetization state and on the faint force exerted by any nearby tiny...