Magnetic hardening of Fe₃₀Co₇₀nanowires

Abstract

3d transition metal-based magnetic nanowires (NWs) are currently considered as potential candidates for alternative rare-earth-free alloys as novel permanent magnets. Here, we report on the magnetic hardening of Fe30Co70 nanowires in anodic aluminium oxide templates with diameters of 20 nm and 40 nm (length 6 μm and 7.5 μm, respectively) by means of magnetic pinning at the tips of the NWs. We observe that a 3-4 nm naturally formed ferrimagnetic FeCo oxide layer covering the tip of the FeCo NW increases the coercive field by 20%, indicating that domain wall nucleation starts at the tip of the magnetic NW. Ferromagnetic resonance (FMR) measurements were used to quantify the magnetic uniaxial anisotropy energy of the samples. Micromagnetic simulations support our experimental findings, showing that the increase of the coercive field can be achieved by controlling domain wall nucleation using magnetic materials with antiferromagnetic exchange coupling, i.e. antiferromagnets or ferrimagnets, as a capping layer at the nanowire tips.

Arrangement at the nanoscale: Effect on magnetic particle hyperthermia

“…The shape anisotropy contribution as the result of particles MNPs alignment (aggregation in a chain) can be revealed by FMR experiments as a shift of the resonance when obtained in parallel (magnetic easy axis) and perpendicular (magnetic hard axis) to the long axis of chains29. The FMR spectra for random and chain samples of 40 nm MNPs are shown in Fig.…”

Simulation of alnico coercivity

“…Interestingly, some of the above features are also encountered in fine-particle and nanowire magnetism [ 22,24,[38][39][40][41][42]. For example, fine particles also exhibit a transition from coherent rotation to curling, and wireend features affect the coercivity [24,25,43].…”

Cylindrical Magnetic Nanowires Applications

“…The large coercivity of thermally treated Cu-doped NWs is attributed to the increase in magnetocrystalline anisotropy energy as a result of bcc lattice strain and changes in the NW microstructure [115], [119]. A different approach for improving the magnetic hardness of NWs consists in exploiting the interfacial exchange between ferromagnetic-antiferromagnetic (FM-AFM) or between ferromagnetic materials with different and high magnetocrystalline anisotropy [120]. As the NWs demagnetize via nucleation from the NW ends or de-pining, any way of stalling this effectively increases the coercive field [104].…”