Preparation And Properties Of Core-shell Magnetic Nanomaterials

As the most promising magnetic material, the two-phase nanocomposite permanentmagnet is likely to enhance the magnetic energy product significantly. In our work, wesynthesized the core-shell type Sm-Co nanoparticles by different chemical methods, such asthe polyol reduction, ultrasonic-assisted polyol reduction and hydrazine hydrate reduction.Meanwhile, the coating effects under different experimental parameters were studied andthe growth mechanism of core-shell Sm-Co nanoparticles was proposed, which provide anew idea of the core-shell type nanoparticles with excellent magnetic properties. Specificresearch progresses are as follow:(1) The poyol reductions of cobalt with different solvents (ethylene glycol,polyethylene glycol200, polyethylene glycol400and1,2propylene glycol) were discussed.It is found that the well-dispersed cobalt nanoparticles can be obtained when using ethyleneglycol as the solvent. The potential mechanism of poyol method is explained.(2) The core-shell type nanoparticles were synthesized by a simple polyol method inethylene glycol solvent. It has been found that a5nm coating, which consists of bothhexagonal close-packed (hcp) and face-centered cubic (fcc) type of cobalt, is formed on thesurface of Sm-Co based nanoparticle. Sm-Co nanoparticle with about10nm Fe3O4shell isalso detected. The coercivity and remanence ratio of Sm-Co@Co nanopariticles andSm-Co@Fe3O4are601.5Oe and1534.8Oe,0.160and0.442, respectively. Moreover, wefind that the coating effect can be impacted by the Co2+:OH-molar ratio, mechanicalstirring, and the surface treatment and properties of Sm-Co based nanoparticles.(3) The polyol method was improved by using sonication. However, the water additionduring the process brings the boiling point of the polyol system down, which results in thefailure of coating.(4) The hydrazine hydrate reduction was used to prepare core-shell type Sm-Conanoparticles. It is found that Co2+can be reduced to hcp-and fcc-type cobalt under thenormal pressure condition. However, the reaction is incomplete. The disadvantage andreaction mechanism were analyzed.