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Cobalt carbide nanoparticles were processed using polyol reduction chemistry that offers high product yields in a cost effective single-step process. Particles are shown to be acicular in morphology and typically assembled as clusters with room temperature coercivities greater than 4 kOe and maximum energy products greater than 20 KJ/m 3 . Consisting of Co 3 C and Co 2 C phases, the ratio of phase volume, particle size, and particle morphology all play important roles in determining permanent magnet properties. Further, the acicular particle shape provides an enhancement to the coercivity via dipolar anisotropy energy as well as offering potential for particle alignment in nanocomposite cores. While Curie temperatures are near 510K at temperatures approaching 700 K the carbide powders experience an irreversible dissociation to metallic cobalt and carbon thus limiting operational temperatures to near room temperature.2

Hexagonal BaFe12O19 ferrite films, having thicknesses ranging from 200–500μm, were prepared by a screen printing process followed by sintering heat treatments. Structural, magnetic, and microwave measurements confirmed that the polycrystalline films were suitable for applications in self-biasing microwave devices in that they exhibited a large remanence (4πMr=3800G), high hysteresis loop squareness (Mr∕Ms=0.96) and low microwave loss. A derivative linewidth ΔH of 310 Oe was measured at 55.6 GHz. This represents the lowest ΔH measured in polycrystalline hexaferrite materials. ΔH can be further improved by reducing porosity and improving the c-axis orientation of grains in polycrystalline ferrite.

Barium hexaferrites (BaFe12O19) are especially useful for microwave/millimeter devices. Due to large ferromagnetic resonance (FMR) loss (linewidths >2kOe), traditional compacts of polycrystalline Ba ferrites indeed hinder the utilization of the materials for practical devices. The present experiment demonstrates that the quasi-single-crystal Ba ferrite disks can be fabricated by a single solid-state reaction technique without liquid phase participation, combining with a processing of alignment for the ferrite seed crystals. The ferrite bulks show a pure hexagonal Ba ferrite phase, an expected 4πMs of 4.48kG, and coercivity of 10∼20Oe along the c axis, similar to the results of a typical single crystal. The FMR measurement indicates that the sample yields an anisotropy field of 16.0kOe and a linewidth of about 300Oe at U-band frequencies. Although the linewidth is broader than ideal Ba ferrite single crystals (ΔH<100Oe), it may be possible to reduce to 100Oe by eliminating pores, cracks, local grain boundary, and nonuniformity. In terms of material preparation, we believe that it is cost effective in the production of future microwave devices.

A miniature, quasi one dimensional, magnetic field sensor based on magnetoelectric coupling is presented. The magnetoelectric sensor makes use of the d31 coupling mode between a piezoelectric lead zirconate titanate tube and FeNi magnetostrictive wire. The sensors demonstrate high sensitivity, high signal-to-noise ratio, and low noise floor at zero DC magnetic bias field and at low frequency resulting in smaller, lower power consumption, and volumetric efficiency. Experiments indicate a zero bias field sensitivity of 16.5 mV/Oe at 100 Hz stemming from a magnetoelectric coefficient of 1.65 V/cm-Oe. The results are quantitatively described by a theoretical model of laminate composites.