Synthesis Of FePt Nanoparticles Research Articles

ChemInform Abstract: Development on Self‐Assembly Technique for Arrangement of Chemically Synthesized FePt Nanoparticles

AbstractReview: 20 refs.

Perpendicular easy axis alignment of FePt nanoparticles on a platinum-(001) buffer layer for high-density magnetic recording

The phenomenon of atomic motion between the nanoparticle and its substrate was examined in constructing perpendicularly aligned FePt nanoparticle structures. Samples of iron-rich FePt nanoparticles synthesized by vapor phase or liquid phase synthesis techniques were deposited on a platinum-(001) buffer layer and annealed in a hydrogen atmosphere. Superconductive quantum interference device and x ray diffraction measurements for the in-plane and out-of-plane direction exhibited perpendicularly oriented magnetization and an L10 ordered phase with a perpendicular easy axis orientation. The coercivity was measured as approximately 4.3 kOe. In addition, high angle annular dark field-scanning transmission electron microscopy showed FePt alloy formation normal to the sample surface. The atomic distribution data showed iron diffusion into the platinum layer. These results might open a new path toward ultrahigh density storage media from chemically synthesized FePt nanoparticles.

(Invited) Development on Self-Assembly Technique for Arrangement of Chemically Synthesized FePt Nanoparticles

This paper reviews our study of bit patterned media (BPM) using L10 (face centered tetragonal)-FePt nanoparticles. For the practical use of L10-FePt nanoparticles to BPM, some breakthroughs are required: a highly ordered two-dimensional array of nanoparticles on a substrate, a controlled orientation of the axis of easy magnetization in vertical direction on a substrate. Previously, we reported about the achievement for uniformity FePt nanoparticles by controlling chemical synthesis conditions. Moreover, we confirmed the selective chemical interaction Pt in the surface of FePt nanoparticles and SH group with (3-mercaptopropyl)tri-methoxysilane (MPTMS). This study presented a new hybrid technique combining the selective chemical bonding and a substrate with a geometrical grid in order to control the array of FePt nanoparticles with uniform direction of their magnetization. We succeed in preparing uniform array of nanoparticles on geometrical grid with size of 200 nm square prepared using ultraviolet nanoimprint lithography (UV-NIL).

Injection of synthesized FePt nanoparticles in hole-patterns for bit patterned media

FePt nanoparticles of uniform sizes, compositions, and crystal structures can be obtained by chemical synthesis. Additionally, the nanoparticles can be well dispersed by the adsorption of a surfactant on the nanoparticle surface. Previously, the immobilization of FePt nanoparticles on a thermal oxide Si substrate was carried out by chemical synthesis, utilizing the Pt–S bonding between the -SH functional group in (3-mercaptopropyl)trimethoxysilane, MPTMS and Pt in FePt nanoparticles. However, controlling FePt nanoparticle arrays by this synthesis method was very difficult. In the present study, we attempted to control the distortion of the arrangement of FePt nanoparticles using an MPTMS layer modified with a silane coupling reaction and a geometrical structure prepared by ultraviolet nanoimprint lithography (UV-NIL). In this study, the hole-patterns used for the geometrical structure on Si(1 0 0) were 200 nm wide, 40 nm deep, and had a 500 nm pitch. The 5.6 nm FePt nanoparticles were used to coat the hole-patterns by using a picoliter pipette. An XHR-SEM image clearly revealed that the FePt nanoparticles were successfully arranged as a single layer with an average pitch of 10.0 nm by Pt–S bonding in the hole-patterns on Si(1 0 0).

X-ray absorption measurements on nanoparticle systems: self-assembled arrays and dispersions

X-ray absorption spectroscopy methods are presented as a useful tool to determine local structure, composition and magnetic moments as well as to estimate the effective anisotropy of substrate supported self-assembled arrays of wet-chemically synthesized FePt nanoparticles. A compositional inhomogeneity within the nanoparticles yields reduced magnetic moments with respect to the corresponding bulk material and may also hinder the formation of the chemically ordered L10 phase in FePt nanoparticles. The latter is indicated by a reduced effective anisotropy, which is one order of magnitude smaller than expected from the known value of the corresponding bulk material.As a new approach, measurements of the x-ray absorption near-edge structure of Fe-oxide nanoparticles in dispersion are presented and ageing effects are discussed on the basis of multiplet calculations.

Chemically synthesized FePt nanoparticles with controlled particle size, shape andcomposition

Monodisperse Fe–Pt nanoparticles have been prepared by thermal decomposition of iron pentacarbonyl[Fe(CO)5] and reduction ofplatinum acetylacetonate [Pt(acac)2] with dibenzyl ether in the presence of oleic acid and oleylamine. The particle composition was adjusted by changing theFe(CO)5/Pt(acac)2 molar ratiowhile fixing the Pt(acac)2 amount. The size of FePt nanoparticles was tuned by controlling the injection temperatureof the iron precursor. The low injection temperature of precursors and the usage ofsurfactants as a reaction solvent, together with a slow heating to a low refluxingtemperature, were found to be the key parameters for the formation of cubic nanoparticles.Nanorods were formed by simply adjusting the injection time of the surfactants. Theas-made nanoparticles had a low coercivity, which was increased to 7 kOe when annealed at800 °C for 1 h.

Phase Transformation in Silica-Coated FePt Nanoparticles

Chemically synthesized FePt nanoparticles (NPs), with an average size of 5.8 nm, were coated with silica (SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) shells. The thickness of the silica shell could be controlled between 7.5-25 nm. A modified heating profile has been adopted with which silica shell cracking at high temperatures (1000degC) could be prevented. Even with prolonged heating for 24 h at 800degC, no sintering of the particles is observed. Low temperature (7 K) and room temperature magnetization scans show low coercivity values which are possibly due to a compositional distribution among the individual NPs.

The Role of Ligands in the Synthesis of FePt Nanoparticles

The monosize formation, the ability of self-assembly, and high coercivity after annealing are the properties that lead to the priority of FePt magnetic nanoparticles for the application in recording media. These nanoparticles were synthesized by the superhydride method. The effect of oleic acid and oleylamin ligands on the fabrication of nanocrystals and the stability of the FePt system has been studied. TEM, EDS, XRD, and spectrophotometer analysis show the formation of FePt nanoparticles dispersion in hexane and indicate that oleylamine increases the number of particles in the nucleation stage and decreases the size of the Pt core, whereas the oleic acid controls the shell of the particle and its growth, and, furthermore, causes the stability of the FePt colloidal systems.

Surface Modification of Chemically Synthesized FePt Nanoparticles

L10-FePt nanoparticle having high magnetic anisotropy is a promising candidate for the future ultra high magnetic recording material. We have succeeded in the fabrication of cubical FePt nanoparticles. It is necessary for high areal recording density to develop a homogeneous assembled technique of the cubical nanoparticle with its magnetic easy axis in the vertical direction on a substrate. It has been known the selective chemical reaction between metal species and functional group of organic molecules. We focused on the selective chemical reaction to control the direction of the magnetic easy axis in the cubical nanoparticle. In this study, the modification of the organic molecule with various functional groups to the surface of the cubical nanoparticle was examined. Consequently, the amino groups were replaced by thiol groups and carboxyl groups on the surface ligands of the nanoparticle were residual, and then, we confirmed bonding thiol group end to Pt atom selectively.

Tailoring nucleation and growth conditions for narrow compositional distributions in colloidal synthesized FePt nanoparticles

To eliminate compositional and size variabilities between individual binary nanoparticles, it is essential to control the mechanistic steps involved in nanoparticle synthesis. A common method for synthesizing FePt nanoparticles involves the simultaneous decomposition and reduction in iron and platinum precursors, respectively. This simultaneous nucleation and growth method yields wide composition and size distributions. This paper describes and experimentally validates a methodology needed to tighten composition and size distributions for this process. By engineering the surfactant chemistry with tertiary phosphines to tightly bind the iron atoms in the iron precursor, uniform platinum rich seeds form during the initial stages of the synthesis. A thermodynamically preferred heterogeneous nucleation of iron atoms into these uniform platinum seeds in the subsequent stages produces a final dispersion with uniform particle-to-particle compositions. The paper addresses the understanding for optimizing the nucleation and growth sequences for compositional control in FePt nanoparticles.

Compositional evolution during the synthesis of FePt nanoparticles

A series of FePt nanoparticles was synthesized by the thermal decomposition of iron pentacarbonyl and reduction in platinum acetylacetonate in phenyl ether solvent. A range of precursor molar ratios of 2, 1.5, and 1 between iron pentacarbonyl and platinum acetylacetonate was studied. After 30 min of reflux, the synthesis method produced a wide distribution in composition and size for the nanoparticles. Given 200 min of reflux, it was observed that the particle-to-particle composition and size narrowed, and the atomic ratio of Fe to Pt, for the majority of nanoparticles, approached the initial precursor molar ratios except for the molar ratio of 1. It is speculated that the compositional variability may be a result of the slow kinetics of iron pentacarbonyl’s decomposition in the reaction.

Surface Modification of Chemically Synthesized FePt nanoparticles

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Lattice expansion in nonoxidized FePt nanoparticles: X-ray absorption measurements

Wet-chemically synthesized FePt nanoparticles were structurally characterized not only in the as-prepared state but also after the removal of organic ligands and reduction in Fe oxides by a soft in situ hydrogen plasma treatment. By the analyses of the extended x-ray absorption fine structures at the Pt ${L}_{3}$ absorption edge, we found an enhanced lattice constant with respect to the bulk material for the oxide-free nanoparticles with clean surfaces. This shows that there exists a lattice expansion in FePt nanoparticles, which is an intrinsic property of the particles, and neither caused by Fe oxides at the surface nor by the organic ligands surrounding the nanoparticles in the as-prepared state. In addition, a first evidence of an inhomogeneous composition within the nanoparticles is given.

Easy control of the size and composition of FePt nanoparticles with Improved synthesis

A new synthesis of FePt nanoparticles with tunable size and composition has been developed. Unlike conventional synthesis methods with which it is difficult to simultaneously control the size and chemical composition of FePt nanoparticles, the new synthesis offers a convenient way to tune FePt nanoparticles with different sizes and compositions. The synthesis involves the simultaneous decomposition of Fe3(CO)12 and reduction of Pt(acac)2 in diethylene glycol. Fe3(CO)12 is a powder (nonvolatile) which is critical in governing the FePt particle size and composition. By varying the amount of surfactants and precursors ratio [Fe3(CO)12∕Pt(acac)2], FePt particles with tunable composition and particle size (2–8nm) can be obtained. After high temperature annealing (∼600°C), Fe50Pt50 nanoparticles are partially transformed to the L10 phase as indicated by the soft and hard components in the hysteresis loops. The coercivity ranges from a few kilo-Oersted to more than 15kOe, depending on the particle size. Dynamic coercivity measurements reveal that the large FePt particles are easier to chemically order than the small FePt particles under the same annealing condition.

Direct Synthesis of Ferromagnetic Fe-Pt Nanoparticles By Using a High-Pressure Chemical Solution Route with Microwave Irradiation

We report direct synthesis of chemically ordered FePt nanoparticles using microwave irradiation during polyol reaction at 250 {degree sign}C under high pressure without any post- synthesis treatments. An X-ray diffraction pattern of as- synthesized FePt nanoparticles shows superlattice peaks. Mössbauer analysis exhibits the FePt nanoparticles having partially ordered L10 structure, and the fraction of Fe atoms in the chemically ordered L10 structure to the total amount of Fe atoms is 57 %. Coercivity and saturation magnetization of the partially ordered FePt nanoparticles are 3.4 kOe and 49 emu/g at room temperature, respectively. An evaluation of the anisotropy-field distribution using Flanders-Shtrikman method reveals that the FePt sample includes nanoparticles with anisotropy fields much lower than the anisotropy field HkWr of 85 kOe obtained by rotational hysteresis loss measurements.

ANNEALING EFFECT ON THE INDUCED MAGNETISM OF PLATINUM IN FePt NANOPARTICLES

Effect of annealing on structural and magnetic properties of non-equatomic chemically synthesized FePt nanoparticles with an average size of 3.2 nm diameter is reported. Annealing of the particles at 700°C resulted in the increase of particles size and the enhancement of total magnetization and coercivity, the latter could be attributed to a transformation from disordered to ordered crystallographic phase. Although the system is far from optimum "equatomic" stoichiometry, coercivity field of 1.1 kOe was obtained at 10 K together with remanence ratio of 0.55. X-ray magnetic circular dichroism spectra recorded at the Pt L 2,3 edges on annealed samples revealed the enhancement of magnetic moment induced on Pt atom.

Array formation and size effects in chemically synthesized FePt nanoparticles

Monodisperse FePt nanoparticles (NP’s) have been synthesized by reduction of platinum acetylacetonate [Pt(acac)2] followed by thermal decomposition of iron pentacarbonyl [Fe(CO)5] in the presence of oleic acid (OA) and oleyl amine (OY) as surfactants at a low reaction temperature. Particle size is controlled by the injection temperature of Fe(CO)5. The effect of particle size on the blocking temperature has been investigated for nanoparticles with sizes of 3.0 and 6.0nm. The interparticle spacing is varied by changing the addition time of the OA and OY. Well-aligned mono- and multi-layered hexagonal-closed-packed (hcp) to square lattice nanostructures are formed for 5nm FePt NP’s. Surfactant layer thickness, ⟨L⟩ to metal core radius R (⟨L⟩∕R) ratios of 0.46 and 0.60 are evaluated for the monolayer of hexagonal-closed-packed and square lattice array structures, respectively. For hcp arrays bilayer and trilayer structures are also observed. Subjecting the NP’s to thermal processing at 800°C results in a transformation of the nanoparticles from the disordered fcc phase to the ordered L10 phase.

Ordering kinetics of chemically synthesized FePt nanoparticles

FePt is a very interesting magnetic material and many attempts have been made towards the lowering of its ordering temperature. Addition of Au and Ag seems to be a satisfying solution, since it can reduce the annealing temperature by 100–150 °C. In the present work, FePtAu and FePtAg nanoparticles have been synthesized via a modification of the polyol method in different compositions. The ideal percentage of the third metal was chosen in order to study its effect on the transformation to the L 1 0 phase. Some attempts have been made to study the ordering kinetics and the role of the third metal.

Synthesis and Magnetic Properties of FePt Nanoparticles with Hard Nonmagnetic Shells

Chemically synthesized FePt nanoparticles were coated with nonmagnetic SiO2 and MnO shells by sol-gel and polyol processes. TEM images show that the FePt/SiO2 nanoparticles exhibit a thick spherical shell. The size and morphology of the MnO shell can be controlled by changing the reaction temperature, the molar ratio of surfactants/Mn(acac)2, and/or the concentration of precursor. The morphology of the MnO shell can be either spherical-like or cubic-like, depending on whether the molar ratio of surfactants/Mn(acac)2 is less than or larger than 2. From XRD measurements, the spherical core/shell nanoparticles exhibit 3D random crystallographic orientation, while the cubic core/shell nanoparticles prefer (200) texture. The magnetic moment of FePt particles can be enhanced by coating with SiO2 and MnO shells. Furthermore, the agglomeration of FePt particles upon the thermal annealing can be significantly inhibited with SiO2 and MnO shells.

Effect of Sintered Grain Growth on Chemical Ordering in Binary FePt/Cu Nanoparticle Arrays

Recent studies have shown a strong correlation between grain growth and chemical ordering in chemically synthesized FePt nanoparticles. In order to study this effect, we have prepared a series of samples in which 3.5 nm FePt nanoparticles are dispersed in a matrix of Cu nanoparticles. The samples were annealed at 600 degrees C and at 800 degrees C. Grain size was determined by XRD Scherrer analysis and time-dependent remanent coercivity measurements were made to determine the intrinsic remanent coercivity, Hcr0. For samples annealed at 600 degrees C, Hcr0 increases strongly with grain size up to approximately 5 nm and increases weakly with additional grain growth. By contrast, after annealing at 800 degrees C, Hcr0 appears nearly independent of grain size. The results suggest that isolated 3.5 nm FePt nanoparticles can be weakly ordered when annealed at 600 degrees C and sintering is necessary for significant chemical ordering.