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

Abstract

Ferrimagnetic insulator Bismuth-substituted YIG (Bi1Y2IG) thin films with thickness from 8.2 nm to 31.7 nm and roughness smaller than 0.5 nm have been grown on substituted Gd3Ga5O12 (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/cm3. 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 Kuλ than un-doped YIG films under same strain. The measured peak to peak linewidth ΔH 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.