Magnetization of cobalt nanodiscs

• Published in: Journal of magnetism and magnetic materials 2006-02, Vol.297 (1), p.54-59
• Main Authors: Waddell, J., Inderhees, S., Aronson, M.C., Dierker, S.B.
• Format: Article
• Language: English
• Subjects: Cobalt nanodiscs; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic anisotropy; Magnetic properties and materials; Magnetic properties of nanostructures; Magnetization reversal; Physics
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2005.02.049

We have studied the magnetization and AC susceptibility of a dilute colloidal dispersion of ε -Co nanodiscs. The temperature dependence of the magnetization implies that the nanodisc moments become largely static below a blocking temperature which exceeds room temperature. The related anisotropy energy is significantly larger than the magnetocrystalline anisotropy for bulk ε -Co, which may result either from surface modifications to the crystalline anisotropy, or perhaps from shape anisotropy. The saturation moment is found to be temperature independent, over a wide range of temperatures and also close to the blocking temperature, although the field at which saturation occurs varies considerably with temperature. A coercive field of 1700 Oe is found at low temperature, indicating that magnetization reversal involves the coordinated rotation of the moments in individual nanodiscs. Aging effects are observed in the AC susceptibility, implying that the spatial coherence of the room temperature dispersions increases over time, leading to static short-range order.