Magnetization and antiferromagnetic coupling of the interface between a 20 nm Y3Fe5O12 film and Gd3Ga5O12 substrate

We present evidence for and characterization of a $\ensuremath{\approx}4\text{\ensuremath{-}}\mathrm{nm}$-thick ${({\mathrm{Y}}_{1\ensuremath{-}x}{\mathrm{Gd}}_x)}₃{\mathrm{Fe}}₅{\mathrm{O}}₁₂$ layer with $x\ensuremath{\ge}0.4$ formed at the interface between a gadolinium gallium garnet (GGG) substrate and a sputtered ${\mathrm{Y}}₃{\mathrm{Fe}}₅{\mathrm{O}}₁₂$ (YIG) epitaxial film with nominal thickness of 20 nm. Temperature-dependent polarized neutron reflectometry (PNR) and superconducting quantum interference device (SQUID) magnetometry show antiferromagnetic alignment of this interfacial layer with the bulk of the YIG film at low $T$ that persists to at least 3 tesla. These experiments also show that this interfacial alignment switches from antiparallel to parallel between 100 and 200 K in small applied magnetic fields. Simple modeling suggests correlation of this crossover with the ferrimagnetic compensation point of the mixed garnet that forms this interfacial layer.