Polyol Process for Fe-based Hard (FCT-FePt) and Soft (FeCo) Nanoparticles

Abstract

The synthesis of magnetic as well as non-magnetic nanoparticles is of fundamental importance for the development of novel technologies based on the properties of the particle itself or nanostructures using the same. Since most of the novel applications demands the use of either metal or alloy magnetic particles, synthesis of the same by using non-aqueous process is preferred. In this paper, we report the synthesis of Fe-based hard (fct-FePt) and soft (FeCo) magnetic materials using modified polyol process. Fe-Pt nanoparticles: Equiatomic FePt nanoparticles with the ordered L1 0 structure is attractive as high-density magnetic recording media. In our recent work, chemically synthesized fcc-FePt nanoparticles with narrow size distribution and their self-assembled array with close-packed microstructure has been achieved successfully. However, the particles coalesced during the subsequent annealing step which is necessary to obtain L1 0 FePt nanoparticles. Later, the authors successfully demonstrated the direct synthesis of L1 0 FePt nanoparticles at low temperatures of 553 K using "modified polyol method" without subsequent annealing, whose diameter is 5-10 nm and intrinsic magnetocrystalline anisotropy field (H k ) of 31 kOe[1]. Partially ordered L1 0 -FePt nanoparticles synthesized in tetraethylene glycol by using polyol process is mostly polycrystalline in nature. Thus attempts were made to prepare single crystal L1 0 -FePt nanoparticles by introducing nucleating and complex agents during the synthesis. Though the fluxuation in physical properties of L1 0 -FePt particles was minimized using hexachloroplatinate (H 2 PtCl 6 ) as the nucleating agent, particles remained polycrystalline in nature. However when carboxylic acid was used along with H 2 PtCl 6 , FePt nanoparticles with more than 50 % ordering was realized under the optimum experimental conditions of Fe:Pt initial mole ratio of 52.5:47.5, 1 at. % of Pt as H 2 PtCl 6 and carboxylic acid, five equivalent weight of Fe. The superlattice reflection lines of (001) and (110) in XRD pattern and the sextets from the Mossbauer spectroscopy at room temperature confirmed the presence of L1 0 phase as shown in Fig 1. The coercivity and anisotropy field of these particles were 5. 6 kOe and more than 40 kOe, respectively as shown in Fig.