No abstract

We explore the nonlinear mixing and amplification of magnetic polariton modes in ultrasmall waveguides. Ultrasmall waveguide geometries can produce large oscillating microwave fields—up to about 500 Oe. Using these large fields, we examine nonlinear ferromagnetic dynamics in ribbons of Permalloy and Fe. In particular if two microwave signals at different frequencies are sent into the waveguide, we can increase the transmission of one wave by adding energy to the other wave. We also demonstrate the creation of new frequencies and the development of a comb of equally spaced frequencies. These experimental results are explained with perturbation theory and micromagnetics calculations.

M-type barium hexagonal ferrite films with the crystallographic c axis out of plane were successfully deposited onto a Pt template using a metallo-organic decomposition technique. For the best film, x-ray diffraction patterns revealed strong (00l) reflections and a texture fraction of 0.953, confirming the out of plane c axis orientation. Atomic force microscopy images confirm hexagonal grains in this film with an average lateral size of ∼500 nm. Hysteresis loops revealed a high effective out of plane anisotropy field, high perpendicular remanent magnetization Mr=0.93 Ms, and out of plane coercivity of 4.5 kOe. Out of plane Ferromagnetic Resonance measurements determined the values of γ=2.79 GHz/kOe and effective anisotropy field. The full width at half maximum FMR linewidth was 338 Oe at 60 GHz. These properties are suitable for possible use in on-wafer millimeter wave devices.

We report the development of a broadband ferromagnetic resonance (FMR) system operating in the frequency range from 10 MHz to 70 GHz using a closed-cycle He refrigeration system for measurements of thin films and micron/nano structures. The system is capable of carrying out measurements in frequency and field domain. Using two coplanar waveguides, it is capable of simultaneously measuring two samples in the out of plane and in plane FMR geometries. The system operates in the temperature range of 27-350 K and is sensitive to less than one atomic monolayer of a single crystal Fe film.

We developed the thin film microwave magnetic material, M-type barium hexagonal ferrite (BaM) doped with Al, for signal processing devices operating above 40 GHz with little to no applied magnetic field. Al was chosen as the dopant material because it significantly increases the already strong anisotropy field of BaM. A series of thin film BaAlxFe12-xO19 samples, x ranging from 0 to 2 in 0.25 steps, were deposited on Pt templates using a metal-organic decomposition growth technique. The resulting films are polycrystalline and highly textured, with the hexagonal c-axis directed out of plane. These films are also self-biasing; easy axis hysteresis loops have a high squareness ratio, s, in the 0.83-0.92 range. As expected, the anisotropy field increases with x, ranging from 1.34 to 2.19 × 106 A/m (16.9-27.5 kOe) for x = 0-2, while the saturation magnetization Ms decreases with x, ranging from 0.334 to 0.175 × 106 A/m (4πMs = 4.2-2.2 kG) for x = 0-2. These values were measured at room temperature, but the temperature dependence of these quantities was also measured below room temperature, down to 30 K. The measured ferromagnetic resonance linewidths, on the order of 12-30 × 103 A/m (140–370 Oe) for compositions below x = 1, indicate device-quality films. Above a certain threshold, the linewidth increases linearly with frequency at a rate of 0.2-0.64 × 103 (A/m)/GHz (2.5-8 Oe/GHz) for x = 0–1, respectively. The behavior of the linewidth is correlated with the structural properties of the films measured using x-ray diffraction and atomic force microscopy. The results of magnetic force microscopy, Curie point measurements, spectral ellipsometry (index of refraction), and magneto-optical measurements are also included and discussed.