Yttrium iron garnet Fe3Y5O12 (YIG) is the material of choice in spin pumping, spin Seeback and Spin Hall magnetoresistance (SHMR) measurements [1-3]. This is mainly due to two properties: a) YIG is a wide band-gap insulator, so it has no free electrons to contribute to the thermal conductivity in the Seebeck effect and b) YIG has a very small Gilbert damping (~10-4) with a narrow resonant peak. The best characteristics are obtained for films grown epitaxially on gadolinium gallium garnet (GGG) substrates.However the Gd from the GGG substrates is know to diffuse into the film. Our objective here is to determine the location of the Gd diffusion and its affects on the magnetic structure of the film. This diffusion is suspected to result in a magnetic dead layer at the bottom and/or on the top of the sample or different regions within it.