THEORY FOR COUPLING FERROMAGNETS THROUGH PARAMAGNETIC LAYERS - DIRECT EXCHANGE COUPLING PLUS A MAGNETIC PUMP MECHANISM

We present a theory for coupling ferromagnets through paramagnetic layers. First, there is a direct ferromagnetic coupling due to the exchange molecular field carried by s-electrons of the ferromagnet into the paramagnetic layers. Second, the non-homogeneous exchange field polarizes the spin charge while pumping away the spin opposite to the field, yielding basically an antiferromagnetic coupling. By introducing a gentle undulating roughness at the interface, the calculation shows an oscillating coupling of 14 layers period. Results for Fe sandwiched with Cu, Cr and Pd are in excellent agreement with experiments and are surface structure dependent. Also the magnetoresistance is roughness dependent and does not oscillate.