Field-dependent thermoelectric power and thermal conductivity in multilayered and granular giant magnetoresistive systems

The giant magnetoresistance (GMR) effect in granular and multilayer thin films has been widely investigated because of possible device applications. Despite this intensive effort, the underlying mechanisms responsible for the effect have not been identified. We present measurements of the thermoelectric power (TEP) and thermal conductivity on a wide variety of granular and multilayer GMR systems. The strong magnetic field dependences of both the TEP and the thermal conductivity are found to be closely related to the magnetoresistance. The TEP measurements require that the high density of states in the ferromagnetic materials play a major role in the GMR effect. The thermal conductivity measurements indicate that the scattering mechanisms in granular samples are elastic while multilayer samples have a significant inelastic, spin-flip component.