Compaction of Co nanowire assemblies with high energy density

Abstract

Single crystalline hcp Co nanowires (NWs) with high coercivity have been synthesized through a facile thermal decomposition method. Controlling the growth parameters makes it possible to vary the mean diameter (from 20 nm to 8 nm) and the mean length (from 120 nm to 165 nm) of Co NWs. The magnetization loops of aligned Co NW assemblies present very high coercivity (HC) up to 10.4 kOe at 300 K. It should be noted that the HC value increases from 6.3 kOe to 10.4 kOe as the average diameter of Co NWs decreases from 20 nm to 10 nm. The high HC in 10 nm Co NW assemblies corresponds to a coherent magnetization reversal mode, which has been confirmed from the angular dependence coercivity measurements. The temperature dependence of HC shows an increasing trend with decreasing temperature and attains a maximum value of 20 kOe at 10 K. The compaction of the pre-aligned NWs assemblies at various pressure results in packing density in the range from 5.3 to 7.3 g/cm3 and energy product as high as 20 MGOe for the bulk samples which is in the intermediate range between Alnico and rare-earth containing magnets