Magnetoelastic and optoelastic coupling in (111)- and (110)-oriented bismuth-iron garnet films prepared by sputter epitaxy

Abstract

High-quality iron-garnet films of composition Gd3−vBivFe5−w−x−yGdw GaxAlyO12−zArz with 1.02≤v≤1.45, 0.01≤w≤0.36, 0.22≤x≤0.24, 0.26≤y≤0.38, and 0.002≤z≤0.014 have been grown epitaxially on (111)- and (110)-oriented gallium garnet substrates with the lattice constant in the range 1.2475≤a0(nm)≤1.2553 by rf magnetron sputtering in argon plasma. For the study of the optoelastic and magnetoelastic properties of these sputter-epitaxial films the lattice mismatch Δa⊥=as−a⊥f has been varied in the range −1.7<Δa⊥(10−2 nm)<0.5 by using substrates with various lattice constants. The near-infrared optical anisotropy normal to (Δnxy) and in the plane (Δnyz) of (110)-oriented films turn out to depend linearly on Δa⊥ over this large range of lattice misfits. No growth-induced contribution has been observed. The same behavior is found for the induced uniaxial (K⊥) and in-plane (K∥) magnetic anisotropy constants at room temperature. The optoelastic coefficients P44 and ΔP, as well as the magnetostriction constants λ111 and λ100 inferred from the measured optical and magnetic anisotropies, respectively, compare well with literature values for the considered film compositions if excess gadolinum is taken as diamagnetic substitution on octahedral lattice sites. The epitaxial structure of the films has been confirmed by the narrow x-ray diffraction linewidth from x-ray double-crystal rocking curves and is supported by the extremely low waveguide losses at 1.33-μm wavelength and the low magnetic wall coercivity, i.e., α=0.15 cm−1 and 60 A m−1, respectively. The structural quality of (110)-oriented films is the same as that of (111)-oriented films.