the third material 20 to be between the chemical potentials in the second material 18 if the third material 20 spin component is down then the electrons will flow from the third material 20 to the second material 18 where the chemical potential of the spin down electron is lower than that in third material 20 if we switch the magnetization of the third material 20 so that the spin component in that component is now spin up electrons will flow from second to third material because the chemical potential of the spin up electrons in the second material 18 is now higher a similar argument also works if we switch the magnetization of the second material 18 while that of third ferromagnetic material 20 is fixed a detailed analysis provides the following result for the magnetization m 2 in the second ferromagnet m sub 2 current u221d b u03b3 sup gt n sub d sup gt 1 u03b3b n sub s sup gt 4r 1 n sub sa n sub ds 1 n sub da n sub ss 3 where 1 n d 1 n 1 n 1 n s 1 n 1 n xa 1 n x gt 1 n x lt 1 n x lt 1 n xs 1 n x gt 1 n x gt x d or s b b gt g lt b lt g gt g lt g gt.