Inverted hysteresis loops in ultrathin epitaxial yttrium iron garnet films

Summary form only given. Partially inverted hysteresis loops have been observed for ultrathin films of yttrium iron garnet (Y/sub 3/Fe/sub 5/O/sub 12/ or YIG). Single-crystalline YIG films were prepared on yttrium aluminum garnet (Y/sub 3/Al/sub 5/O/sub 12/ or YAG) substrates by pulsed laser deposition. The film thickness was varied from 100 /spl Aring/ to 4600 /spl Aring/. Epitaxial growth of YIG on YAG was obtained in spite of the lattice mismatch of 3%. [111] and [110] oriented substrates were used in order to study in-plane anisotropy, which is found to be only uniaxial for the films deposited on [110] oriented substrates. The magnetic hysteresis loops recorded for ultrathin YIG films are partially inverted at room temperature. This can be explained by an antiferromagnetic coupling between two different magnetic phases whose presence was detected by ferromagnetic resonance measurements. A composition study by secondary ion mass spectroscopy shows interdiffusion of Fe and Al occurs at the film/substrate. The interaction field between these two phases is determined from measurements of the minor hysteresis loops.