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

TL;DR

This work demonstrates the epitaxial growth of Er-substituted YIG thin films on GGG by pulsed laser deposition across Er contents x=0.008–0.20. Structural characterization confirms single-crystal, fully coherent growth with sharp interfaces and lattice evolution from expansion to contraction as Er increases. Magnetic measurements show systematic decreases in saturation magnetization and the emergence of in-plane uniaxial anisotropy with Er doping, alongside a progressive increase in ferromagnetic resonance damping and linewidth broadening. For low Er content (x≈0.008), damping remains close to undoped YIG, while higher Er levels significantly broaden FMR and increase damping, highlighting a regime where optical functionality from Er3+ can be integrated with low-loss magnetization dynamics for hybrid optomagnonics and microwave-to-optical transduction.

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.

Figures (3)

• Figure 1: Structural characterization of Er:YIG films on GGG (111). (a) XRD $\theta$–$2\theta$ scans for different Er contents ($T_\mathrm{g}=750~^{\circ}\mathrm{C}$). (b) XRD $\theta$–$2\theta$ scan of the Er$_{0.20}$:YIG/GGG sample measured over a larger $2\theta$ range. (c) RSM of the (642) reflection for the Er$_{0.20}$:YIG/GGG sample. (d) STEM image of the Er$_{0.10}$:YIG/GGG interface, imaged along the $[11\bar{2}]$ zone axis. (e) RHEED patterns recorded in the PLD chamber before (top) and after (bottom) Er$_{0.10}$:YIG thin-film growth. (f) Unit cell volumes of all Er:YIG films, extracted from in-plane and out-of-plane lattice constants obtained via XRD (panel (a)) and RSM (panel (c)) measurements, plotted for varying Er contents and growth temperatures.
• Figure 2: (a) Saturation magnetization ($M_\mathrm{s}$) of the Er:YIG films as a function of Er content for samples grown at different substrate temperatures. The dashed-dotted line indicates the $M_\mathrm{s}$ of an undoped YIG reference film. (b) Longitudinal MOKE hysteresis loops recorded at $\lambda=405$ nm with the in-plane magnetic field applied along the easy axis. (c) Polar plots of the remanent magnetization, normalized to $M_\mathrm{s}$, versus the in-plane field angle $\phi$ ($\phi=0^{\circ}$ corresponds to the $[\bar{1}10]$ crystallographic direction). (d) Longitudinal MOKE hysteresis loops measured with the in-plane field applied along the hard axis. Panels (b)-(d) correspond to films grown at $T_\mathrm{g}=800~^{\circ}\mathrm{C}$. (e) Uniaxial magnetic anisotropy constant ($K_\mathrm{u}$) of the Er:YIG films, extracted from the slope of hard-axis hysteresis loops.
• Figure 3: (a) VNA-FMR spectra of Er:YIG films and an undoped YIG film measured under an in-plane magnetic field of 100 mT. (b) FMR linewidths of all Er:YIG films measured at 5 GHz. (c) Frequency dependence of the FMR linewidth for the Er$_{0.008}$:YIG film. The linear fit yields a Gilbert damping parameter $\alpha=9\times{10^{-4}}$ and an inhomogeneous linewidth broadening $\Delta{f}_0=5$ MHz. (d) Gilbert damping parameter and (e) inhomogeneous linewidth broadening as a function of Er content.