Due
to the issues associated with rare-earth elements, there arises
a strong need for magnets with properties between those of ferrites
and rare-earth magnets that could substitute the latter in selected
applications. Here, we produce a high remanent magnetization composite
bonded magnet by mixing FeCo nanowire powders with hexaferrite particles.
In the first step, metallic nanowires with diameters between 30 and
100 nm and length of at least 2 μm are fabricated by electrodeposition.
The oriented as-synthesized nanowires show remanence ratios above
0.76 and coercivities above 199 kA/m and resist core oxidation up
to 300 °C due to the existence of a >8 nm thin oxide passivating
shell. In the second step, a composite powder is fabricated by mixing
the nanowires with hexaferrite particles. After the optimal nanowire
diameter and composite composition are selected, a bonded magnet is
produced. The resulting magnet presents a 20% increase in remanence
and an enhancement of the energy product of 48% with respect to a
pure hexaferrite (strontium ferrite) magnet. These results put nanowire–ferrite
composites at the forefront as candidate materials for alternative
magnets for substitution of rare earths in applications that operate
with moderate magnet performance.
We have studied the precessional dynamics of Co/Cu/Py (where Py = Ni81Fe19) trilayers by time-resolved x-ray resonant magnetic scattering at the synchrotron radiation facility BESSY II. We have found that the magnetic precessional decay time of Fe magnetic moments in Py layers decreases when changing the mutual orientation of the magnetization direction of Py and Co layers from parallel to antiparallel. The observed changes of the decay time can be associated with the spin pumping induced damping effect.
Internal magnetic structure of dextran coated magnetite nanoparticles in solution using small angle neutron scattering with polarization analysis J. Appl. Phys. 109, 07B513 (2011); 10.1063/1.3540589Magnetoresistive effects in Co/Pd multilayers on self-assembled nanoparticles (invited) J. Appl. Phys. 107, 09C506 (2010); 10.1063/1.3350909Small angle x-ray and neutron scattering study of disordered and three dimensional-ordered magnetic protein arrays J. Appl. Phys. 105, 07B528 (2009); 10.1063/1.3075865Formation of magnetic nanocrystals in a glass ceramic studied by small-angle scattering Cobalt and magnetite nanoparticles were studied with small-angle x-ray and neutron scattering methods under grazing incidence for analyzing their structural and magnetic correlation on silicon substrates. The Co nanoparticles are in the ferromagnetic state while the iron oxide nanoparticles are superparamagnetic at room temperature. After spin-coating the iron oxide particles with a diameter of 20 nm and a very narrow size distribution of only 6% show very nice self-ordering on silicon substrates with nearly perfect six-fold symmetry as can be derived from scanning electron microscopy (SEM) images and from grazing incidence small angle x-ray scattering results. In contrast the dropcasted cobalt nanoparticles show a much higher roughness and less ordering. The corresponding SEM images and grazing incidence small angle neutron scattering maps with polarization of the incident beam reveal less pronounced structural and magnetic correlation.
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