Comparison of the magnetic properties of bismuth substituted thulium iron garnet and yttrium iron garnet films

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronics applications. Bismuth substituted iron garnets are particularly popular among these various films because Bi3+ with a larger ion radius can adjust the lattice constant, strain state, and PMA of the films. In this paper, Tm2BiFe5O12 (TmBiIG) and Y2BiFe5O12 (YBiIG) garnet films with a series of thicknesses are prepared by radio frequency magnetron sputtering, and these films exhibit robust PMA. The microstructural properties, magnetic properties, and the anomalous Hall effect of these two kinds of films are discussed in detail. Due to their larger magnetostriction coefficient and proper tensile strain, TmBiIG films exhibit better PMA than YBiIG films, which have lower damping. As the thickness of TmBiIG and YBiIG films increases, the PMA becomes weaker, and the 40 nm YBiIG turns back to in-plane easy magnetization, but PMA is still obvious for the 64 nm TmBiIG. The ferromagnetic resonance linewidth of the 32 nm TmBiIG film is 249.08 Oe @ 13 GHz, and the damping factor is 1.49 × 10−2, which is close to that of Tm3Fe5O12. YBiIG films have better damping characteristics than TmBiIG films; however, the value is larger than that of yttrium iron garnet because of surface roughness and defects caused by larger lattice mismatch. In addition, on account of fewer defects and smaller surface roughness, the Hall voltage and Hall resistivity in TmBiIG/Pt heterostructures are larger than in YBiIG/Pt.