  We propose a device that can operate as a magneto-resistive switch or
oscillator. The device is based on a spin-thermo-electronic control of the
exchange coupling of two strong ferromagnets through a weakly ferromagnetic
spacer. We show that the local Joule heating due to a high concentration of
current in a magnetic point contact or a nanopillar can be used to reversibly
drive the weak ferromagnet through its Curie point and thereby
exchange-decouple the strongly ferromagnetic layers, which have an antiparallel
ground state. Such a spin-thermionic parallel-to-antiparallel switching causes
magnetoresistance oscillations where the frequency can be controlled by proper
biasing from essentially DC to GHz.
