Thin Films*

One of the major challenges in the field of spin-current based electronics is the development of low-loss ferromagnetic insulators capable of generating spin currents without an accompanying charge current. Bulk phase Li_0.5Fe_2.5O₄ (LFO) is known to have the lowest Gilbert damping parameter (α ≈ 0.002) among the spinel ferrites, but the growth of LFO thin films with desirable microwave properties has remained elusive due to the volatility of lithium. In this talk, we demonstrate the realization of epitaxial LFO ultra-thin films (~3nm) on MgAl₂O₄ substrates with an ultra-low damping of α ≈ 0.0005 and an FMR linewidth of 7.5 Oe at 15GHz. These values rival those of yttrium iron garnet (YIG), the gold standard of low-loss magnetic insulators. LFO also offers distinct advantages over YIG such as smaller external field requirements and thinner interfacial layers crucial for magnetic switching. Our results place LFO as an attractive new candidate for low-loss microwave materials in the field of spintronics.