Magnetotaxial Perpendicular Magnetic Anisotropy and Enhanced Faraday Rotation in Ion Beam Sputtered Cerium-Substituted Yttrium Iron Garnet.

Abstract

Ferrimagnetic iron garnets are valuable for photonic and spintronic devices because of their large magnetooptical (MO) effects and tunable magnetic anisotropy and domain structures. In particular, cerium-substituted yttrium iron garnet (Ce:YIG) has an excellent MO figure of merit in the near-infrared region. However, achieving perpendicular magnetic anisotropy (PMA) in Ce:YIG films has conventionally relied on strain engineering, constraining the relationship between substrate lattice parameters and magnetic properties. We demonstrate strain-independent PMA in epitaxially grown Ce:YIG (Ce_0.9Y_2.1Fe₅O₁₂) films on two different (111)-oriented garnet substrates using ion beam sputtering. Despite opposite strain states (tensile and compressive), both films exhibit robust PMA with labyrinth-shaped magnetic domains with widths of 219 nm. Comprehensive surface and interface characterization reveals high-quality epitaxial growth with coherent film-substrate interfaces. The films demonstrated superior MO performance with a Faraday rotation of -1.05°/μm and a figure of merit of 74.7°/dB at 1064 nm wavelength. Detailed anisotropy analysis reveals that magnetotaxial (growth-induced) anisotropy of up to ∼30 kJ/m³ dominates over magnetoelastic contributions, enabling strain-independent PMA formation. Three-dimensional (3D) micromagnetic simulations confirm mixed Néel-Bloch domain wall configurations. This work demonstrates that PMA in Ce:YIG films can be achieved through magnetotaxial anisotropy independent of the substrate strain state, providing valuable insights for magnetooptical material design.