Circumferential and longitudinal 1GHz permeabilities in Co-rich melt-extracted amorphous wires

We have analyzed the circumferential and longitudinal permeabilities of Co-rich amorphous wires cast by melt-extraction. All samples were simultaneously driven by microwave fields and submitted to static fields, the two kinds of fields being always perpendicular in order to induce a ferromagnetic resonance. A 1 GHz relative circumferential permeability of about 25 was obtained at a static field of 320 Oe. The loss ratio (the imaginary part of the permeability to the real part) was as small as 0.2 in this case. These data characterize wires with low losses and high permeability, which are useful for microwave applications. The majority of these applications require a longitudinal drive field, which explains our interest in the longitudinal permeability. Problems arise from different demagnetizing effects in different points of the wire surface and higher static fields are required in order to evaluate this permeability. The longitudinal permeability at 850 Oe was found to be lower than the circumferential permeability at 320 Oe, whereas the loss ratio was about the same. Microwave applications such as antennas, core transformers and magneto-dielectrics can be developed using these wires.