No abstract

A hexagonal ferrite thin film-based planar millimeter-wave phase shifter was demonstrated. The device made use of an M-type barium ferrite ͑BaM͒ thin film prepared by pulsed laser deposition and a coplanar waveguide geometry. The phase tuning relied on ferromagnetic resonance in the BaM film. The device showed a phase tuning rate of 43°/ ͑mm kOe͒ and an insertion loss of 3.1 dB/mm in the on-resonance regime. In off-resonance regimes, the device showed smaller loss and smaller tuning rates. The experimental results were confirmed by theoretical calculations.

A procedure is developed to study the evolution of high anisotropy magnetic recording media due to thermally activated grain reversal. It is assumed that the system is composed of single domain grains that evolves by passing through a sequence of relatively long-lived metastable states punctuated by abrupt reversals of individual grains. Solutions to the rate equations describing the sequence of metastable states are calculated using kinetic Monte Carlo. Transition rates are formulated from the Arrhenius-Néel expression in terms of the material parameters, temperature, and applied field. Results obtained from this method are shown to be in good agreement with those calculated from finite-temperature micromagnetics. The method is applied to study the rate dependence of finite-temperature MH loops and the thermal degradation of a recorded bit pattern in perpendicular recording media. A significant advantage of the procedure is its ability to extend simulations over time intervals many orders of magnitude greater than is feasible using standard finite-temperature micromagnetics with relatively modest computational effort.

Recently there has been interest in small, planar, high frequency (10–50 GHz) signal processing devices which are based on metallic ferromagnets. This paper, in contrast, presents theoretical results for devices utilizing a hexagonal ferrite. The notch filter results show attenuation of frequencies in the 40–60 GHz range with applied fields in the 1–5 kOe range. For geometries similar to the ultrasmall metallic devices, the transmission loss at the notch can be from 20 to 140 dB/cm depending on the thickness of the hexagonal ferrite film and the inclusion of dielectric spacers. The phase shifter results show phase shifts of up to 360°, with losses below 2 dB/cm. These results are obtained for devices using thin films around 1 μm in thickness for the hexagonal ferrite, and for reasonable linewidths below 200 Oe.

A Kinetic Monte-Carlo algorithm is applied to examine MH loops of dual-layer magnetic recording media at finite temperature and long time scales associated with typical experimental measurements. In contrast with standard micromagnetic simulations, which are limited to the ns-μs time regime, our approach allows for the direct calculation of magnetic configurations over periods from minutes to years. The model is used to fit anisotropy and coupling parameters to experimental data on exchange-coupled composite media which are shown to deviate significantly from standard micromagnetic results. Sensitivities of the loops to anisotropy, inter-layer exchange coupling, temperature, and sweep rate are examined.