We report here a new synthetic route to FePt nanoparticles using a stoichiometric mixture of Na2Fe(CO)4 and Pt(acac)2. The structure of FePt nanoparticles, their size, chemical composition, and magnetic property can be controlled by various synthetic parameters, such as the solvent type, nature, and molar ratio of surfactants and stabilizers, synthesis temperature, and purification process. Partially ordered fct (L10) nanoparticles with room temperature magnetic coercivity can be synthesized directly in tetracosane solution at 389 degrees C. The fcc FePt synthesized in nonadecane can be transformed into the magnetically important fct phase at 430 degrees C without significant particle sintering.

We report the synthesis of FePt magnetic nanoparticles using Na2Fe(CO)4 and Pt(acac)2 as reagents. This method allows good control over particle stoichiometry and ensures efficient mixing of Fe and Pt atoms in the alloy at the atomic scale. The use of a variety of different high boiling solvents and different surfactants allows control over particle size. Materials can be prepared in the disordered face-centered cubic (fcc) structural form and converted to the high magnetocrystalline anisotropy face centered tetragonal (fct or L10 structure) at lower temperatures than those prepared by other routes. By using solvents such as nonadecane, docosane, and tetracosane, we can prepare samples directly in the fct form. Preformed fcc particles prepared by this method can also be transformed in solution to the fct structure. Samples have been characterized by a combination of diffraction, electron microscopy, thermogravimetric, and magnetic measurements.

A simple microwave heating method has been used for the stoichiometrically controlled synthesis of FePt and FePd nanoparticles using Na 2 Fe(CO) 4 and Pt(acac) 2 /Pd(acac) 2 as the main reactants. By varying the solvents and surfactants, the microwave assisted reactions have shown a significant advantage for the rapid production of monodisperse fcc FePt nanoparticle metal alloys which can be converted to the fct phase at low temperatures (364 uC). Microwave reactions at high pressure (closed system) have led to the direct formation of a mixture of fcc and fct phase FePt nanoparticles. Room temperature structural and magnetic properties of materials have been characterized by X-ray diffraction, HRTEM and magnetic measurements. The onset of ordering has been investigated by in situ high temperature X-ray diffraction studies.

In this paper, a systematic investigation of the microstructure, high performance magnetic hardness as well as novel magnetic memory effect of the Pr(4)Fe(76)Co(10)B(6)Nb(3)Cu(1) nanocomposite magnet fabricated by conventional melt-spinning followed by annealing at temperatures ranging from 600 to 700 degrees C in Ar gas for nanocrystallization are presented and discussed. Transmission electron microscopy (TEM) observation confirms an ultrafine structure of bcc-Fe(Co) as a magnetically soft phase and Pr(2)Fe(14)B as a hard magnetic phase with a spring-exchange coupling in order to form the nanocomposite state. Electron diffraction analysis also indicates that the Co atoms together with Fe atoms form the Fe(70)Co(30) phase with a very high magnetic moment (2.5 mu(B)), leading to a high saturation magnetization of the system. High magnetic hardness is obtained in the optimally heat-treated specimen with coercivity H(c) = 3.8 kOe, remanence B(r) = 12.0 kG, M(r)/M(s) = 0.81 and maximum energy product (BH)(max) = 17.8 MG Oe, which is about a 25% improvement in comparison with recent results for similar compositions. High remanence and reduced remanence are the key factors in obtaining the high performance with low rare-earth concentration (only 4 at.%). High-resolution TEM analysis shows that there is a small amount of residual amorphous phase in the grain boundary, which plays a role of interphase to improve the exchange coupling. Otherwise, in terms of magnetic after-effect measurement, a magnetic memory effect was observed for the first time in an exchange-coupled hard magnet.

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