Role of the density of states in the giant magnetoresistance of magnetic multilayers

The role of the density of states in the giant magnetoresistance (GMR) of ferromagnet 1 (FM1)/nonmagnetic (NM = Cu)/ferromagnet 1 (FM1) sandwiches has been investigated by inserting a thin layer of the second ferromagnetic material (FM2 = Co) at the FM1/Cu interfaces. As the thickness of the inserted layer increases, the GMR increases to a value seen for purely Co/Cu/Co sandwiches. By using differing FM1 materials [e.g., Py (permalloy (Ni80Fe20), Ni, Fe] we observe the exponential increase in GMR as more Co is inserted to be dependent on the FM1 material behind it. This is explained by realizing that although the GMR is dominated by the scattering caused by defects like those at the FM2 material/Cu interface, the nature of the scattering depends on the density of states of the FM1 material. This result is discussed in terms of advanced theories on the origin of the GMR in magnetic multilayers. (C) 2000 American Institute of Physics. [S0021-8979(00)58408-4].