Temperature dependent resonant microwave absorption in perpendicular magnetic anisotropy epitaxial films of a spinel ferrite
2019
We report on the temperature (T), magnetic field (μ0H), and angle (Θ, Φ) dependent resonant absorption of X-band microwaves in spinel ferrite epitaxial films subjected to two distinct states of growth strain. The polar angle (Θ) dependence of the resonance field (Hres) in films with ∼0.5% ab-plane expanded unit cell establishes a distinct perpendicular magnetic anisotropy (PMA). The anisotropy field (Han┴) for Θ = 0° increases monotonically on lowering the temperature from 300 K to 90 K following the behavior of the saturation magnetization (Ms) keeping Han┴/Ms ≈ 1. The narrow resonance linewidth (μ0ΔHres┴ = 3.7 mT at 300 K) and its negligible (±0.3 mT) variation with temperature establish the magnetic softness of these PMA films. The dependence of Hres on Θ, Φ, and T in films subjected to compressive stress shows in-plane cubic anisotropy whose strength is nonmonotonic in temperature. The ∼2.0% compression of the unit cell basal plane also appears to accentuate noncollinearity of sublattice magnetization of such films as indicated by the T-dependence of ΔHres. The thicker films with PMA display spin wave resonances whose position allows determination of the spin wave stiffness constant together with independent determination of Han┴. The resonance characteristics of the PMA films qualify them as potential candidates for frequency agile microwave devices and magnonic circuit elements.We report on the temperature (T), magnetic field (μ0H), and angle (Θ, Φ) dependent resonant absorption of X-band microwaves in spinel ferrite epitaxial films subjected to two distinct states of growth strain. The polar angle (Θ) dependence of the resonance field (Hres) in films with ∼0.5% ab-plane expanded unit cell establishes a distinct perpendicular magnetic anisotropy (PMA). The anisotropy field (Han┴) for Θ = 0° increases monotonically on lowering the temperature from 300 K to 90 K following the behavior of the saturation magnetization (Ms) keeping Han┴/Ms ≈ 1. The narrow resonance linewidth (μ0ΔHres┴ = 3.7 mT at 300 K) and its negligible (±0.3 mT) variation with temperature establish the magnetic softness of these PMA films. The dependence of Hres on Θ, Φ, and T in films subjected to compressive stress shows in-plane cubic anisotropy whose strength is nonmonotonic in temperature. The ∼2.0% compression of the unit cell basal plane also appears to accentuate noncollinearity of sublattice magnetization...
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