Geometrical Dependence of Magnetoresistivity in Bismuth Microwire Arrays

Geometrical dependence of the magnetoresistivity using polycrystalline bismuth microwire array was measured under magnetic fields of 0-2 T at temperatures of 50-300 K, and its diameter of prepared microwire arrays were 10 and 25 mum. Aspect ratio, defined by wire length divided by the diameter, was determined for the wire array since both edges of all wires were attached to Ti thin film layer in order to avoid contact resistance. The attachment of the layer makes it possible to estimate the resistivity of the wire arrays. Both resistivities of the wire arrays at 300 K were equal to approximately 1.35 muOmegam and were good agreement not only at 300 K but also in temperature region of 50-300 K in the absence of a magnetic field. Although the magnetoresistivities of both samples increased in the presence of the magnetic field, the behavior of magnetoresistivity depended on wire diameter. The magnetoresistivity of the wire array with higher aspect ratio was suppressed even if the resistivities of both samples without magnetic field are equal. The difference of magnetoresistivities was remarkable in high magnetic field and low temperature region. Therefore, the thermoelectric element with high aspect ratio such as micro- and nano-wire array leads suppression of magnetoresistivity increase more than that of bulk material