Magnetoresistance in thin wires with granular structure

We report on studies of magnetotransport properties and structure at 5-300 K temperature region in glass-coated microwires prepared from immiscible (Co10Cu90 and Co29Ni25Mn1Cu45) elements. The crystalline structure consists of nanocrystals of Co (Ni) and Cu with average grain size below 30 nm. Considerable magnetoresistance (MR) (up to about 18%) is found in Co10Cu90 microwires depending on fabrication parameters. Magnetic field dependence of MR of Co10Cu90 microwires is completely un-hysteretic showing monotonic decay with magnetic field. On the other hand, MR (up to about 4%) is also found in as-prepared and annealed Co29Ni25Mn1Cu45 microwires. Annealing of Co29Ni25Mn1Cu45 microwires (973 K) results in increasing of the coercivity (Hc) from 65 up to 750 Oe. Annealed Co29Ni25Mn1Cu45 sample exhibits considerable hysteresis on magnetic field dependence of MR. Neutron and X-ray diffraction allows to attribute changes in magnetic properties and MR after annealing of Co29Ni25Mn1Cu45 microwires to the decomposition of the metastable phase.