Strong Perpendicular Anisotropy and Anisotropic Landé Factor in Bismuth-Doped Thulium Garnet Thin Films

Abstract

With the development of spintronics, garnet films with perpendicular magnetic anisotropy (PMA) have been attracting the attention of researchers for decades. In this work, bismuth-doped thulium iron garnet (Tm2BiFe5O12, TmBiIG) films of varying thickness having strong PMA effect were fabricated on substituted Gd3Ga5O12 (sGGG) (111) substrates using the pulsed laser deposition (PLD) technique. Crystallographic characterization and magnetic properties of TmBiIG films were investigated using high-resolution scanning transmission electron microscopy, X-ray diffraction, vibrating sample magnetometry, and broadband ferromagnetic resonance (FMR). A high perpendicular anisotropic field of H⊥ = 4,445 ± 7.5 Oe in a 10-nm-thick film and H⊥ = 4,582 ± 7.7 Oe in a 30-nm-thick film at room temperature were obtained and analyzed in detail. Surprisingly, an additional spin-wave mode was observed in the in-plane FMR spectra. The discrepancy between in-plane and the out-of-plane Landé g-factors established a correlation with the PMA effect in the TmBiIG films. The Landé g-factor of the TmBiIG films is much lower than that of free electrons, indicating that the strong spin–orbit coupling is caused by Tm and Bi heavy elements. The Gilbert damping factor α changed from 0.007 to 0.012 in various thicknesses of TmBiIG films.