Structural analysis and magnetic properties of solid solutions of Co–Cr system obtained by mechanical alloying

Abstract

In this paper, a systematic study on the structural and magnetic properties of Co100−xCrx alloys (0<x<100, Δx=10) obtained by mechanical alloying is presented. Co and Cr elemental powders were used as precursors, and mixed in an adequate weight ratio to obtain Co1−xCrx (0<x<100, Δx=10). Mechanical milling was carried out at room temperature in a shaker mixer mill using vials and balls of hardened steel as the milling media with a ball:powder weight ratio of 10:1. The mixtures were milled for 7h. Results shown that after 7h of milling time, solid solutions based on Co-hcp, Co-fcc and Cr-bcc structures were obtained. The saturation polarization indicated a maximum value of 1.17T (144Am2/kg) for the Co90Cr10, which decreases with the increasing of the Cr content up to x=80, as a consequence of the dilution effect of the magnetic moment which is caused by the Cr content and by the competition between ferromagnetic and antiferromagnetic exchange interactions. The coercivity increases up to 34kA/m (435Oe) for Co40Cr60. For Cr rich compositions, it is observed an important decrease reaching 21kA/m (272Oe) for Co10Cr90, it is related to the grain size and the structural change. Besides, the magnetic anisotropy constant was determined for each composition. Magnetic thermogravimetric analysis allowed to obtain Curie temperatures corresponding to the formation of hcp-Co(Cr) and fcc-Co(Cr) solid solutions.