Millimeter Wave Parametric Amplification with Antiferromagnetic Materials

Abstract

The use of material with natural magnetic resonances in the millimeter and submillimeter wave bands makes possible electromagnetic interaction without an extremely large applied magnetic field. Antiferromagnetic materials most suitable for microwave application Cr2O3 and MnFe2 display resonances at approximately 160 and 250 kMc. In the presence of a magnetic field applied parallel to the sublattice magnetizations, the uniform precessional mode resonates at different frequencies for oppositely directed circularly polarized excitation. A perturbation analysis has been conducted to determine the parametric response of the oppositely directed uniform precessional modes to longitudinal pumping. For materials with a sufficiently narrow linewidth, very close coupling between the uniform precessional mode on an external coaxial, stripline, or waveguide signal circuit is possible. Calculations have been conducted on the response of an antiferromagnetic medium in a silver cavity resonant to the pump frequency. The pump power absorbed by the cavity at the threshold of amplification for Cr2O3 would be 2(10)4 w. Narrower linewidth materials are needed for efficient antiferromagnetic millimeter and submillimeter amplification. A more efficient utilization of the pump power and a simplified structure for millimeter wave application results when the pump fields are supported by a dielectric rod mode resonance. If the rod is placed across the narrow dimention of rectangular waveguide, the broad metallic wall forms the conducting end plates of the H11 mode. The signal TE01 waveguide mode couples to the appropriately directed circularly polarized uniform precessional resonance of the antiferromagnetic material on the rod.