High-Power Effects in Flame-Sprayed and Hot-Pressed Nickel-Aluminum-Gallium Spinels

Abstract

Significant improvements on high-power handling capability of ferrites in the nickel-aluminum-gallium spinel system (NAGS) have been obtained by hot pressing these materials. The materials investigated were NiAlxGayFe2−(x+y)O4, where x+y was 0.975. The x/y ratio was varied from 2.24:1 to 2.95:1. Cavity measurements were made on these samples at S band to approximately 2 MW peak which is equivalent to approximately 35 rf Oe. Nonlinearity was determined by observing the decrease in the peak of susceptibility χ″ at an applied field required to maximize χ″. Results are compared to samples prepared by conventional ceramic techniques in this system and in the magnesium-manganese-iron system. Conventionally prepared and flame-sprayed materials in the nickel-aluminum-gallium spinel system showed an improvement of approximately ten times in power handling capability over a ferrite in the magnesium manganese system. Samples of nickel-aluminum-gallium spinels that were hot pressed showed a hundred times improvement in the power handling capability compared to the magnesium manganese ferrite. A description of the techniques and procedures required for flame spraying and hot pressing materials in this system is given.