Magnetic properties of nanometric Fe wires obtained by multiple extrusions

A method for producing arrays of nanometric wires is briefly described. The method consists of extruding a compact containing parallel iron wires spaced in a copper matrix until the wires become extremely small (10 nm at the ultimate stage). Coercive forces up to 0.04 T are found. A clear shape-induced anisotropy is observed. The decrease in H_A observed at the smallest diameters is attributed to wire distortion. The activation volume deduced from magnetic aftereffect measurements is 6×10⁴ nm³ . It is much larger than the one expected in the case of coherent rotation. Its value is rather consistent with a collective magnetization reversal process. The angular dependence of H_C approaches a 1/cos θ law. This behavior excludes coherent rotation. It is expected whenever the coercive field is much weaker than the anisotropy field in the activation volume