Characterization of Superparamagnetic “Core−Shell” Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic “Solid Solution” Nanoalloys

Park, Jong Il; Kim, Min; Jun, Young‐wook; Lee, Jae Sung; Lee, William R.; Cheon, Jinwoo

doi:10.1021/ja049649k

Cited by 200 publications

(130 citation statements)

References 29 publications

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“…Co@Au (core@shell) NPs exhibit a reduced magnetic anisotropy compared to monometallic Co NPs [41] . However, the magnetic properties of Co@Pt NPs are similar to those for Co NPs, with a particle size similar to the size of the Co core [42] . Fe@Au MNPs show similar magnetic moments to those of bulk iron [43] .…”

Section: Polymetallic Npsmentioning

confidence: 75%

Application of alternative energy forms in catalytic reactor engineering

Houlding

Rebrov

2012

Green Processing and Synthesis

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This review provides a general overview of recent applications of magnetic nanoparticles for controlled radiofrequency (RF) heating in catalytic synthesis, mass transfer enhancement in laminar fl ow and magnetic separation. By directly delivering RF energy to magnetic materials, issues such as long heating periods and energy losses can be minimized. The main mechanisms of RF heating are briefl y reviewed. The effect of nanoparticles size, shape and composition on the effi ciency of RF heating is discussed. RF energy has been shown to be effective in many applications, however, it is still not used in chemicals due to high equipment costs.

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Section: Polymetallic Npsmentioning

confidence: 75%

Application of alternative energy forms in catalytic reactor engineering

Houlding

Rebrov

2012

Green Processing and Synthesis

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“…The presence of the charge-transfer signatures in the Co XANES is consistent with the formation of a bimetallic alloy, as opposed to a coreϪshell structure. 31 To further probe the environment of the Pt and Co atoms in these structures, EXAFS measurements were used to determine the local bonding characteristics. This technique relies on the characteristic interference pattern between the outgoing photoelectrons from the absorbing atom and backscattered photoelectrons coming off of neighboring atoms.…”

Section: Resultsmentioning

confidence: 99%

“…6 The Co shell could then undergo postsynthetic oxidation upon exposure to air during the magnetic and spectroscopic measurements, resulting in the formation of CoO as suggested by the EXAFS data. In another bimetallic system, calculations performed for Ru 31 Pt 6 clusters adsorbed on carbon predict migration of Pt atoms to the cluster surface as a result of the stronger binding of Ru to the carbon substrate which acts as a driving force for segregation. 32 It should be noted that the predicted CoO shell is likely to be extremely thin.…”

mentioning

confidence: 99%

Probing Compositional Variation within Hybrid Nanostructures

et al. 2009

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Ќ These authors contributed equally to this work. P latinum-based bimetallic alloys are highly desirable for their potential in magnetic storage, sensing, and catalysis, 1Ϫ5 often displaying properties that are independent of their constituent materials. 6 In addition to changes in the geometric distribution of the individual atoms, the unique structure and bonding in bimetallics can also lead to alterations in the electronic structure of the material. For example, PtNi alloys show enhanced activity for oxygen reduction relative to pure Pt, 7 as do similar alloys, including Pt 3 Co.8 However, bimetallic nanomaterials are not as well-understood outside of singlecrystalline studies or theoretical modeling, and the practical application of more complex nanostructures is further complicated by factors such as varied growth conditions, the presence of surface stabilizing agents, and the increased surface-to-volume ratio of nanoscale materials. Bimetallic nanoparticles have even been shown to undergo dynamic metal segregation in response to oxidizing or reducing environments. 9As nanostructured systems increase in complexity, the potential for structural and compositional variations with respect to the individual components rises dramatically. Hybrid nanostructures, the combination of two or more nanoscale materials to form a new heterostructure, are being actively pursued for a number of applications, 10 including device integration and assembly, 11Ϫ13 chemical and biological sensing, 14,15 and photocatalysis. 16Ϫ23 In particular, the integration of a metallic component with an optically active semiconductor, directly in solution, can lead to novel materials that exhibit new functionalities that result from the coupling between the individual components. For example, photocatalytic heterostructures can promote efficient charge separation across a metalϪsemiconductor junction, followed by catalytic reaction at the surface of the metal component.The development of semiconductorϪ metal hybrid nanostructures for magnetic and catalytic applications requires a thorough understanding of the metallic structure, which is difficult to predict for a complex system where nucleation and growth proceeds on the tip of a semiconductor. In a previous communication, we reported the selective growth of Pt, PtCo, and PtNi nanoparticles on the tips of CdS rods in solution. 24 Here, we present a detailed analysis of the structural and magnetic properties of PtCoϪCdS hybrid structures in comparison to similar free-standing PtCo nanoparticles. X-ray absorption spectroscopy (XAS) is utilized as a sensitive probe for identifying subtle differences in the local structure and composition of the hybrid materials, which can be difficult to discern using traditional analytical methods such as electron microscopy and X-ray diffraction (XRD). While the electronic and atomic structures of noble metal-based bimetallic alloys and free-standing PtCo

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“…[15][16][17][18] Therefore, the nanoscaling laws of engineered magnetic nanoparticles are important not only to understand the behavior of existing materials but also to develop novel materials with superior properties. Biomedical applications of such artificially engineered magnetic nanoparticles are promising since they can be useful as next-generation probes and vectors, which can significantly advance the current clinical diagnostic and therapeutic methods.…”

Section: Figurementioning

confidence: 99%

Nanoscaling Laws of Magnetic Nanoparticles and Their Applicabilities in Biomedical Sciences

2008

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Magnetic nanoparticles, which exhibit a variety of unique magnetic phenomena that are drastically different from those of their bulk counterparts, are garnering significant interest since these properties can be advantageous for utilization in a variety of applications ranging from storage media for magnetic memory devices to probes and vectors in the biomedical sciences. In this Account, we discuss the nanoscaling laws of magnetic nanoparticles including metals, metal ferrites, and metal alloys, while focusing on their size, shape, and composition effects. Their fundamental magnetic properties such as blocking temperature (T b ), spin life time (τ), coercivity (H c ), and susceptibility ( ) are strongly influenced by the nanoscaling laws, and as a result, these scaling relationships can be leveraged to control magnetism from the ferromagnetic to the superparamagnetic regimes. At the same time, they can be used in order to tune magnetic values including H c , , and remanence (M r ). For example, life time of magnetic spin is directly related to the magnetic anisotropy energy (K u V ) and also the size and volume of nanoparticles. The blocking temperature (T b ) changes from room temperature to 10 K as the size of cobalt nanoparticles is reduced from 13 to 2 nm. Similarly, H c is highly susceptible to the anisotropy of nanoparticles, while saturation magnetization is directly related to the canting effects of the disordered surface magnetic spins and follows a linear relationship upon plotting of m s 1/3 vs r -1. Therefore, the nanoscaling laws of magnetic nanoparticles are important not only for understanding the behavior of existing materials but also for developing novel nanomaterials with superior properties.Since magnetic nanoparticles can be easily conjugated with biologically important constituents such as DNA, peptides, and antibodies, it is possible to construct versatile nano-bio hybrid particles, which simultaneously possess magnetic and biological functions for biomedical diagnostics and therapeutics. As demonstrated in this Account, nanoscaling laws for magnetic components are found to be critical to the design of optimized magnetic characteristics of hybrid nanoparticles and their enhanced applicability in the biomedical sciences including their utilizations as contrast enhancement agents for magnetic resonance imaging (MRI), ferromagnetic components for nano-bio hybrid structures, and translational vectors for magnetophoretic sensing of biological species. In particular, systematic modulation of saturation magnetization of nanoparticle probes is important to maximize MR contrast effects and magnetic separation of biological targets.

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Characterization of Superparamagnetic “Core−Shell” Nanoparticles and Monitoring Their Anisotropic Phase Transition to Ferromagnetic “Solid Solution” Nanoalloys

Cited by 200 publications

References 29 publications

Application of alternative energy forms in catalytic reactor engineering

Application of alternative energy forms in catalytic reactor engineering

Probing Compositional Variation within Hybrid Nanostructures

Nanoscaling Laws of Magnetic Nanoparticles and Their Applicabilities in Biomedical Sciences

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