Temperature Dependence of the Magnetoresistance and Magnetism for MA Co_xCu_100-x Alloys

Abstract

Co_xCu_100-x binary alloys with Co concentrations of x = 5 - 30 were produced by mechanical alloying. We examined the magnetoresistance (MR) and magnetism in the temperature range from 5 K to 300 K for the as-milled Co_xCu_100-x alloys, and investigated the relationship between the MR and the magnetization. The MR for the as-milled samples is characterized as follows: (1) For samples with x ≤ 15, the MR ratio increases at low temperature (5.5% at 5 K), and changes in proportion to the square of the magnetization, M², (2) for a sample with x = 20, the MR ratio measured at temperatures below 120 K shows a constant value (∼3%), and is not proportional to M² in this temperature range, and (3) for samples with x ≥ 25, the MR ratio decreases with decreasing temperature, and is not proportional to M². The magnetization measured at high temperature shows superparamagnetic behavior for samples with x ≤ 20, and has a ferromagnetic component for samples with x ≥ 25.