Bi-YIG ferrimagnetic insulator nanometer films with large perpendicular magnetic anisotropy and narrow ferromagnetic resonance linewidth

摘要

Ferrimagnetic insulator Bismuth-substituted YIG (Bi_1Y_2IG) thin films with thickness from 8.2 nm to 31.7 nm and roughness smaller than 0.5 nm have been grown on substituted Gd_3Ga_5O_(12) (sGGG) substrate by pulsed laser deposition (PLD). A comprehensive description of the structural characteristics and magnetic properties of Bi-YIG films were given. Thickness-dependent large perpendicular magnetic anisotropy (PMA) was induced in Bi-YIG films by tensile strain originate from lattice mismatch. MOKE and VSM results showed that the 8.2 nm and 17.8 nm film has large PMA, high squareness and small out-of-plane coercivity with a saturation magnetization of 115 emu/cm~3. However, with the increasing of film thickness, the easy axis turned from out-of-plane to in-plane. The thickness-dependent PMA indicated that the increase in PMA was caused by the interfacial strain. Furthermore, the Dzyaloshinskii-Moriya interaction (DMI), which is proportional to the strength of spin orbit coupling could also contribute to the increasing of PMA. First-principles calculations were adopted to study the elastic properties of Bi-YIG films. It showed that the Young's modulus of Bi-YIG increased to 225 GPa, which giving a larger K_u~λ than un-doped YIG films under same strain. The measured peak to peak linewidth AH of Bi-YIG film with PMA is 20 Oe for fields out-of-plane. The derived Gilbert damping constant is 7.03 × 10~(-4) indicating a low magnetic loss.