Packing fraction dependence of the coercivity and the energy product in nanowire based permanent magnets.

The maximum magnetic performance which can be expected from elongated single domain particle based permanent magnets is assessed. The results are derived using micromagnetic calculations to model the behavior of large bundles of aligned nanowires. In particular, we discuss the cases of Co and Fe nanowires and their packing fraction dependence of coercivity, which is the main limiting factor. We show that it is, in principle, feasible to achieve BHmax values close to 300 kJ/m3 in Co nanowires with a packing fraction p = 0.7 and close to 400 kJ/m3 at p = 0.85. The packing fraction limitations are essentially non-existing due to the intrinsic magnetocrystalline anisotropy of Co. On the other hand, if a low anisotropy material such as Fe could be produced in the form of fine, well crystallized wires it could yield a BHmax close to 200 kJ/m3 at an optimum p = 0.7. As the performance of iron nanowires is solely based on shape anisotropy it becomes coercivity limited above p = 0.35. [ABSTRACT FROM AUTHOR]