Fabrication And Characterization Of Size And Shape-Controllable Magnetic Nanoparticles

Magnetic nanoparticle is an important class of recording media with huge potential application in the biomedicine fields which has become one of the hot points for nanotechnology research. This paper reviews recent advances in FePt nanoparticles research progress and chose XRD, TEM, VSM techniques to characterize the as‐synthesized FePt/Fe3O4nanoparticles. The main contents are following:1. Using Fe(acac)₃ and H2_PtCl₆ 6H₂O as precursors, via NaBH₄ one‐step reduction combine with Vc two‐step reduction as well as polyol reduction process to synthesis FePt nanoparticles. We study the effect of surfactant on the size, morphology and magnetic properties of the as‐synthesized FePt nanoparticle.2. A method of one‐step reduction by NaBH₄ in the presence of surfactant poly(N‐vinyl‐2‐pyrrolidone) (PVP) was employed to produce monodisperse FePt nanocrystals. The results confirm that the PVP contents have an effect on the transition degree while no significant effect on the particles size. We consume the PVP most probably plays the role of the"catalyst", proper amount of PVP induces the easier transformation of the nanocrystals. The highest coercivity of 5.2 KOe was obtained with the adjusted PVP / FePt molar ratio of 7 when annealed at 500℃for 30 min.3. A convenient surfactant CTAB was chose to assist synthesis of worm‐like FePt nanoparticles. The shape and size evolution ranging from worm‐like to spherical and from 4 to 8 nm were observed, respectively. Growth of worm‐like nanoparticles was monitored by nano‐micelles formed by surfactant CTAB. Further magnetic analysis also revealed the modification of Ms arise from anisotropic shape of nanoparticles4. FePt nanoparticles with different morphologies were successfully prepared in the presence of surfactant sodium dodecyl benzene sulfonate (SDBS) with the addition of different molar ratio of surfactant SDBS to precursors FePt (SDBS/FePt) by a one‐step NaBH₄ reduction approach. And the morphologies show spherical, irregular schistose and dendritic structure when changing the molar ratio of SDBS/FePt. And the magnetic energy product show the largest at SDBS/FePt = 9:1. We deduce this is the result of differences in nanoparticle morphology.5. FePt nanoparticles with flower‐like assembly are synthesized at room temperature when chose PEG as the surfactant. The shapes are composed of fusiform and spherical with the mean sizes of 19.2 nm and 4.9 nm respectively. These fusiform"petals"and spherical"stamens"were found to assemble into flower‐like structures. We suggest the formation of flower‐like assemble of FePt nanoparticles is result from the surfactant assemblage. VSM indicates that Ms nearly eighteen‐fold increase when compared to nanoparticles synthesized under identical conditions except for using PVP as surfactant.6. The complex surfactants oleic acid and oleylamine; citric acid and polyethylene glycol ( PEG) as well as single surfactant sodium dodecyl benzene sulfonate( SDBS)were chose to stabilize the FePt nanoparticles. The characterizations indicate that the complex surfactants induced to produce anisotropic morphologies, and the complex surfactants PEG and citric acid lead to rice‐shape and rod‐shape nanostructure. VSM results show that the spherical particles have the largest Ms while the rod‐shape nanoparticles possess the smallest Ms.7. FePt nanoparticles are synthesized at room temperature by polyol 1, 2‐dodecanediol reduction in the presence of oleic acid, oleylamine and dibenzyl ether. The particles size were tuned from 2.3‐8.8nm by varying the volume ratio of oleic acid / oleylamine, the size and number of quadrilateral particles increase with the amount of oleylamine.8. Multi‐step NaBH₄ combine with ascorbic acid reduction process was chose to synthesis FePt nanoparticles. The effects of annealing temperatures on the magnetic properties of FePt have been investigated. The results confirmed that The annealing treatment caused an increase of coercivity as high as 3KOe at 600℃. However the increscent of coercivity was slight at high temperatures of 550℃which may be caused by the agglomeration of nanoparticles during the annealing treatment.9. Based on the cooperation of surfactants, metal precuesor and liquid environment, monodisperse magnetite (Fe₃O₄) nanoparticles have been prepared by 1, 2‐dodecanediol reduction of iron acetylacetonate (Fe(acac)₃) in the presence of oleic acid, oleylamine and dibenzyl ether. The effect of surfactants concentration on the particles size and morphology were examined. Compared with particles synthesized without surfactants, the use of oleic acid and oleylamine suppressed the growth of magnetite nanoparticles and gave rise to smaller particle size. In addition, suitable concentration of surfactants makes for the uniformity of particles size and shape.