Magnetic and Transport Properties of M-Cu (M = Co, Fe) Microwires

We report on magnetic, transport and structural properties of Co_x-Cu_100−x (5 ≤ x ≤ 30) and Fe₃₇Cu₆₃ glass-coated microwires prepared by the Taylor-Ulitovsky method. The objective of the reported work is to develop a novel functional materials exhibiting giant magnetoresistance (GMR). For Co-Cu microwires with x = 5 we observed the resistivity minimum at 40 K associated with the Kondo-like behaviour but magnetoresistance is small. For x ≥ 10 magnetoresistance reaches 9 % at low temperatures. Temperature dependence of susceptibility shows considerable difference for x > 10 and x ≤ 10 attributed to the presence of small Co grains embedded in the Cu matrix for x ≥ 10. By X-ray diffraction we found, that the structure of Co_x-Cu_100−x microwires for x ≥ 10 is granular consisting of two phases: fcc Cu appearing in all the samples and fcc α-Co presented only in microwires with higher Co content. Structure of Fe₃₇Cu₆₃ microwires consists of Cu nanograins with average grain size of around 40 nm and α-Fe nanocrystals with average grain size ranging between 6 and 45 nm depending on samples geometry. These microwires also exhibit GMR (up to 7.5 % at 5 K).