CoPt Nanowires by Electrodeposition

CoPt nanoparticles with L1$_{0 }$structure have been studied as a promising material for high density magnetic recording due to the high anisotropy value of the L1$_{0}$ phase (K=2x10$^{7}$ ergs/cc). In this study, we prepared CoPt nanowires (up to 200nm in diameter and 100 micrometer in length) embedded in anodized alumina templates by electrodeposition. The pH values have been varied from 3 to 6 by adding diluted NaOH into the deposition bath. The wires were then annealed in a high vacuum furnace at a temperature range between 650$^{o}$C to 750\r{ }C in order to transform their structure from the disordered fcc phase to the ordered L1$_{0}$ phase. A higher pH value leads to a higher coercivity and smoother loop which can be attributed to a more uniform CoPt composition through out the wires. HRTEM data of as-made samples shows that the long wires consist of both tiny nanoparticles (1-2 nm) and elongated nanorods having a single crystal fcc structure. The microstructural data is consistent with the magnetic measurements, showing a slightly preferred orientation perpendicular to the long axis of the wires with H$_{c }$= 5 kOe and 5.5 kOe along and perpendicular to the direction of the wires, respectively.