1 research outputs found
Strongly Exchange Coupled Core|Shell Nanoparticles with High Magnetic Anisotropy: A Strategy toward Rare-Earth-Free Permanent Magnets
No full textAntiferromagnetic(AFM)|ferrimagnetic(FiM)
core|shell (CS) nanoparticles
(NPs) of formula Co<sub>0.3</sub>Fe<sub>0.7</sub>O|Co<sub>0.6</sub>Fe<sub>2.4</sub>O<sub>4</sub> with mean diameter from 6 to 18 nm
have been synthesized through a one-pot thermal decomposition process.
The CS structure has been generated by topotaxial oxidation of the
core region, leading to the formation of a highly monodisperse single
inverted AFM|FiM CS system with variable AFM-core diameter and constant
FiM-shell thickness (∼2 nm). The sharp interface, the high
structural matching between both phases, and the good crystallinity
of the AFM material have been structurally demonstrated and are corroborated
by the robust exchange-coupling between AFM and FiM phases, which
gives rise to one among the largest exchange bias (<i>H</i>
<sub>E</sub>) values ever reported for CS NPs (8.6 kOe) and to a
strongly enhanced coercive field (<i>H</i>
<sub>C</sub>).
In addition, the investigation of the magnetic properties as a function
of the AFM-core size (<i>d</i>
<sub>AFM</sub>), revealed
a nonmonotonous trend of both <i>H</i>
<sub>C</sub> and <i>H</i>
<sub>E</sub>, which display a maximum value for <i>d</i>
<sub>AFM</sub> = 5 nm (19.3 and 8.6 kOe, respectively).
These properties induce a huge improvement of the capability of storing
energy of the material, a result which suggests that the combination
of highly anisotropic AFM|FiM materials can be an efficient strategy
toward the realization of novel rare-earth-free permanent magnets
