Magnetic properties of ${\mathrm{Cu}}_{80}$${\mathrm{Co}}_{20}$ and ${\mathrm{Cu}}_{80}$${\mathrm{Co}}_{15}$${\mathrm{Fe}}_5$ melt-spun ribbons

The magnetic properties of granular, annealed, melt-spun ribbons of the "giant" magnetoresistors, ${\mathrm{Cu}}_{80}$ ${\mathrm{Co}}_{20}$ and ${\mathrm{Cu}}_{80}$ ${\mathrm{Co}}_{15}$ ${\mathrm{Fe}}_5$, have been studied by a variety of techniques. These include x-ray dfiffraction, electron microscopy, ferromagnetic resonance, SQUID magnetometry, Mössbauer-effect spectroscopy, and magnetoresistance. We utilize each of these measurements to reveal different aspects of the particle size distribution as a function of annealing temperatures. These melt-spun alloys require large magnetic fields for magnetic saturation, impairing their utility as magnetic sensors. However, the properties of melt-spun ribbons provide an understanding of why all granular magnetic materials are difficult to saturate. The magnetoresistance ratio of these alloys is maximized by a 500°C anneal with $\frac{\Delta \rho }{\rho }\cong 14\%$ at 4.2 K. The paramagnetic fraction determined by SQUID magnetometry at 4.2 K is 33% for this annealing temperature. The paramagnetic fraction determined by Mössbauer spectroscopy is 14% for samples annealed by 500°C, and vanishes when the sample is annealed at 900°C. The discrepancy between the two measurements of the paramagnetic fraction is due to the vastly different averaging times of the two techniques.