Magnetic Coupling in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><mml:msub><mml:mi mathvariant="normal">Y</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Fe</mml:mi><mml:mn>5</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>12</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:msub><mml:mi>Gd</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:msub><mml:mi>Fe</mml:mi><mml:mn>5</mml:mn></mml:msub><mml:msub><mml:mi mathvariant="normal…

Ferrimagnetic Y$_3$Fe$_5$O$_{12}$ (YIG) is the prototypical material for studying magnonic properties due to its exceptionally low damping. By substituting yttrium with other rare earth elements that have a net magnetic moment, we can introduce an additional spin degree of freedom. Here, study coupling in epitaxial Y$_3$Fe$_5$O$_{12}$/Gd$_3$Fe$_5$O$_{12}$ (YIG/GIG) heterostructures grown by pulsed laser deposition. From bulk sensitive magnetometry and surface Seebeck effect (SSE) Hall magnetoresistance (SMR) measurements, determine alignment heterostructure magnetization through temperature external field. The ferromagnetic between Fe sublattices YIG GIG dominates overall behavior heterostructures. Due dependent gadolinium compensation point total bilayer system be identified. This shifts lower temperatures increasing thickness parallel iron moments. We show control tuning individual layers, opening up large playground devices based on coupled insulators. These could potentially magnon transport analogously electron giant magnetoresistive devices.