Formation Mechanism via a Heterocoagulation Approach of FePt Nanoparticles Using the Modified Polyol Process

Abstract

Herein, we report a new approach of an FePt nanoparticle formation mechanism studying the evolution of particle size and composition during the synthesis using the modified polyol process. One of the factors limiting their application in ultra-high-density magnetic storage media is the particle-to-particle composition, which affects the A1-to-L10 transformation as well as their magnetic properties. There are many controversies in the literature concerning the mechanism of the FePt formation, which seems to be the key to understanding the compositional chemical distribution. Our results convincingly show that, initially, Pt nuclei are formed due to reduction of Pt(acac)2 by the diol, followed by heterocoagulation of Fe cluster species formed from Fe(acac)3 thermal decomposition onto the Pt nuclei. Complete reduction of heterocoagulated iron species seems to involve a CO-spillover process, in which the Pt nuclei surface acts as a heterogeneous catalyst, leading to the improvement of the single-particle composition control and allowing a much narrower compositional distribution. Our results show significant decreases in the particle-to-particle composition range, improving the A1-to-L10 phase transformation and, consequently, the magnetic properties when compared with other reported methods.

Composition‐Mediated Order‐Disorder Transformation in FePt Nanoparticles

“…For example, for an array of NPs of average composition Fe 50 Pt 50 , σ = 1.1 at%, and with a Gaussian distribution of compositions, the number of NPs with compositions outside the pure L1 0 phase region of 42-58 at% Fe in the bulk phase diagram [ 22 ] would be ≈ 1 NP per three trillion. Current compositional standard deviations are larger than this, in the range of 2.1-23 at%, [ 28,29,[42][43][44] which means that, at best, ≈ 1 out of 7000 NPs would fall outside the pure L1 0 region. Therefore, further synthetic advances are needed, if chemically synthesized FePt NPs are to be realized for BPM.…”

“…A total of six NPs could have their phase unambiguously identifi ed, and all six NPs were found to have both L1 0 and L1 2 phases ( Figure 2 ). The average composition of the NPs containing both L1 0 FePt and L1 2 FePt 3 was Fe 38 Pt 62 ( σ at% = 3.3), while the average composition of the remaining NPs whose phase could not be unambiguously identifi ed was Fe 44 Pt 56 ( σ at% = 3.0). A t-test indicates with 99% confi dence that these subsets are statistically different, where the null hypothesis is for the composition of the L1 0 /L1 2 mixed-phase NPs to be equal to that of the NPs whose structures could not be determined.…”

Luminomagnetic Silica-Coated Heterodimers of Core/Shell FePt/Fe3O4 and CdSe Quantum Dots as Potential Biomedical Sensor

“…The first step of synthesis involves the modified polyol process to obtain spherical FePt nanoparticles. This method is widely used in the literature to synthesize nanoparticles with controlled shape, size, and chemical composition, as well as narrow size distribution, that is, monodisperse systems [37,38]. As-synthesized FePt nanoparticles presented average diameter and standard deviation ( ± SD) of 4.0 ± 0.2 nm in a monodisperse system measured by TEM analysis ( TEM ), average composition of Fe 55 Pt 45 , and face-centered cubic (fcc) crystallographic phase, as in a good agreement with the previously reported work [35].…”

Investigation of Surfactant Effect on Size Distribution of FePt-based Nanoparticles by Synchrotron SAXS and TEM

“…Furthermore, the size distributions agree with TEM images that sample B has a narrower distribution and sample A consists of two groups of nanoparticles with comparable fractions. According to the heterocoagulation model of FePt formation in the modified polyol process [17], the existence of iron oxide with Pt-rich nanoparticles leads to the large morphological and size variation.…”