Magnetic and structural properties of epitaxial Er-substituted yttrium iron garnet films grown by pulsed laser deposition

TL;DR

This study demonstrates the successful epitaxial growth of Er-substituted yttrium iron garnet films with preserved low magnetic damping and added optical properties, suitable for hybrid quantum magnonics and transduction applications.

Contribution

It reports the first epitaxial growth of Er:YIG films with controlled Er content, maintaining low damping and structural integrity for optomagnonic use.

Findings

Gradual decrease in saturation magnetization with Er content

Emergence of in-plane magnetic anisotropy at higher Er levels

Low Er-doped films retain near-isotropic magnetization and low damping

Abstract

Er-substituted yttrium iron garnet (Er:YIG) holds the potential of combining the low magnetic damping of YIG with the telecom-band optical transitions of $\text{Er}^{3+}$ ions, making it a suitable material for hybrid optomagnonic devices and microwave-to-optical quantum transduction. We report the epitaxial growth of $\text{Er}_{x}\text{Y}_{3-x}\text{Fe}_{5}\text{O}_{12}$ films with $x=0.008-0.20$ on (111)-oriented gadolinium gallium garnet (GGG) substrates using pulsed laser deposition. X-ray diffraction, reciprocal space mapping, and scanning transmission electron microscopy confirm single-phase, fully coherent growth with atomically sharp interfaces across the entire substitution range. Magnetometry reveals a gradual decrease in saturation magnetization with increasing Er content, consistent with antiparallel coupling between Er$^{3+}$ spins and the net Fe$^{3+}$ moments, along with the emergence of an in-plane uniaxial magnetic anisotropy. The ferromagnetic resonance broadens with Er concentration due to increased Gilbert damping and inhomogeneous linewidth broadening. Films with low Er content ($x=0.008$), most relevant for optomagnonic applications, retain nearly isotropic magnetization and exhibit a damping parameter only slightly higher than that of undoped YIG. These results identify growth and substitution conditions that preserve YIG's low-loss magnetic properties while introducing optical functionality, establishing Er:YIG as a viable platform for hybrid quantum magnonics and microwave-to-optical transduction.