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Journal Article•DOI•

Strategies to tailor the architecture of dual Ag/Fe-oxide nano-heterocrystals—interfacial and morphology effects on the magnetic behavior

Pablo Tancredi1, O. Moscoso Londoño2, P.C. Rivas Rojas1, Ulrike Wolff3, Leandro M. Socolovsky4, Marcelo Knobel2, Diego Muraca2 •
University of Buenos Aires1, State University of Campinas2, Leibniz Association3, National Technological University4
29 Jun 2018-Journal of Physics D (IOP Publishing)-Vol. 51, Iss: 29, pp 295303
TL;DR: In this article, the authors presented the synthesis protocols to obtain two sets of heterocrystals, each one with different morphology: dimer and flower-like, and investigated the magnetization behavior of these hybrid nano-heterocrystals.
Abstract: Bifunctional nanostructured architectures have shown appealing properties, since a single entity can combine the diverse properties of its individual constituents. Particularly, by growing Fe-oxide domains over Ag nanoparticles, the plasmonic and superparamagnetic properties can be combined in a single particle. Beyond the multifunctionality of this system, there are several properties that emerge from intrinsic factors, such as: interface and/or morphology. In this study, we present the synthesis protocols to obtain two sets of heterocrystals, each one with different morphology: dimer and flower-like. In addition, the magnetization behavior of these hybrid nano-heterocrystals is investigated and discussed. These nanomaterials were built by a seed assisted heterogeneous nucleation process, carried out in organic solvents of high boiling point, using the same batch of silver nanoparticles with a mean size of 6 nm as seeds, and tuning the electron-donor capacity of the reaction environment at the thermal decomposition of the iron precursor. Ag/Fe3O4 heterocrystals with dimer and flower-like morphologies were obtained. The synthesis protocols for generating these types of nanomaterials are discussed step-by-step. Structural and morphological properties were determined by transmission electron microscopy, x-ray diffraction and x-ray absorption fine structure. DC magnetization results suggest that the silver/magnetite coupling generates an increase of the blocking temperature in comparison to those obtained from pure magnetite. This behavior could be linked to a possible increase in the magnetic anisotropy produced by an additional disorder at the Ag–Fe3O4 interface. The higher interface area of the Ag/Fe3O4 heterocrystals with flower-like architecture leads to a higher blocking temperature and a stronger magnetic anisotropy. These results are supported by AC susceptibility data.

Summary (2 min read)

Jump to: [Introduction] – [Experimental Details] – [Characterization] – [Results and Discussion] and [Conclusions]

Introduction

  • In the last years, a prominent part of the research in nanochemistry has focused on the preparation of multifunctional and heterostructured nanocrystals, capable of combining two or more inorganic materials into a single system through a direct atomic bond at the interface and without the presence of a molecular bridge [1-3].
  • In these peculiar nanostructures, the optical properties of metallic nanoparticles and the magnetic properties of Feoxide counterparts can be coupled.
  • The most common process to produce heterostructured nanocrystals is the so-called seed-assisted method, where a second component is heterogeneously nucleated over previously formed nanoparticles (“seeds”) of a first component.
  • Many efforts have been dedicated to the understanding of the synthesis conditions and mechanisms that lead to these different morphologies [2, 11-13], mainly because the macroscopic properties of the system can be controlled or tuned by the interface type and the interactions between the different constituents.
  • A discussion on the structural and optical properties is also presented to reinforce the results and the conclusions.

Experimental Details

  • All chemicals were used as received without further purification.
  • Finally, the system was cooled down to room temperature and the AgNPs were precipitated by the addition of ethanol and isolated by centrifugation at 3000 RPM for 15 minutes.
  • The isolated solid was washed 3 times before redispersed in hexane.
  • AgNPs were used as fixed seeds for Fe3O4 heterogeneous nucleation, also known as Ag/Fe3O4 heteroparticles formation.

Characterization

  • Phase composition and crystallographic characterization were carried out via X-ray diffraction (XRD) on a standard Rigaku diffractometer with Cu K-α radiation.
  • These measurements were performed at the Brazilian Synchrotron Light Laboratory (CNPEM/LNLS, Campinas, Brazil).
  • Absorption spectra, carried out on colloidal samples (nanoparticles dispersed in toluene), were recorded at room temperature by means of a UV-VisNIR Shimadzu UV-1603 using quartz cuvettes with 10 mm optical path length.
  • DC magnetization and AC magnetic susceptibility measurements were recorded with a MPMS-XL7 Quantum Design SQUID magnetometer and a PPMS Quantum Design magnetometer, respectively.
  • This mixture was stirred until the toluene was evaporated.

Results and Discussion

  • The two-step procedure employed for the Ag/Fe3O4 heteroparticles synthesis can be conveniently used to study the reaction mechanism and the conditions that lead to the formation of different heterostructure morphologies.
  • Some authors also suggest that Fe3O4 growth over the Ag seed does not always occur epitaxially, leading to nearly independent surface plasmonic properties of the metallic nanoparticles [19].
  • Furthermore, by comparing the obtained results from the Ag/Fe3O4 with those one from the Fe3O4 control sample, one can affirm that the environment of Fe-atoms located in the heterostructures are disposed to form an iron oxide with a stoichiometric Fe3O4 phase.

Conclusions

  • Controlled synthesis protocols were employed to obtain magnetic-plasmonic nanoheterostructures of Ag/Fe3O4 with two distinct morphologies.
  • In the flower-like sample, the dipolar interactions between the Fe-oxide nanoparticles are stronger than in dimer-like counterpart.
  • The maximum of the zero-field-cooling curve was shifted around 90 K and 170 K for dimer and flower-like samples, respectively.
  • Brazilian Nanotechnology National Laboratory (LNNano/CNPEM) is acknowledged for the use of TEM JEOL JEM 2100 (21789) facilities.

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Journal of Physics D: Applied Physics
ACCEPTED MANUSCRIPT
Strategies to tailor the architecture of dual Ag/Fe-oxide nano-
heterocrystals - Interfacial and morphology effects on the magnetic
behavior
To cite this article before publication: Pablo Tancredi et al 2018 J. Phys. D: Appl. Phys. in press https://doi.org/10.1088/1361-6463/aaccc3
Manuscript version: Accepted Manuscript
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This content was downloaded from IP address 130.64.11.153 on 14/06/2018 at 16:18
Strategies to tailor the architecture of dual Ag/Fe-oxide nano-heterocrystals - Interfacial
and morphology effects on the magnetic behavior
P. Tancredi
1
, O. Moscoso Londoño
2,3
*, P.C. Rivas Rojas
1
, U. Wolff
4
, L. M. Socolovsky
5
, M.
Knobel
2
, and D. Muraca
2
1
Laboratorio de Sólidos Amorfos, Instituto de Tecnologías y Ciencias de la Ingeniería “Hilario
Fernández Long”, Facultad de Ingeniería, Universidad de Buenos Aires – CONICET, Buenos
Aires, Argentina
2
Laboratório de Materiais e Baixas Temperaturas, Instituto de Fïsica ‘Gleb Wataghin’,
Universidade Estadual de Campinas, Campinas, Brazil
3
Facultad de Ingeniería, Universidad Autónoma de Manizales, Antigua Estación del Ferrocarril,
Manizales, Colombia.
4
IFW Dresden, Leibniz Institute for Solid State and Materials Research, Dresden,
Helmholtzstrasse 20, 01069 Dresden, Germany
5
Facultad Regional Santa Cruz, Universidad Tecnológica Nacional - CIT Santa Cruz
(CONICET), Río Gallegos, Argentina
*Corresponding author: omoscoso@ifi.unicamp.br, oscar.moscosol@autonoma.edu.co
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Abstract
Bifunctional nanostructured architectures have shown appealing properties, since a single entity
can combine the diverse properties of its individual constituents. Particularly, by growing Fe-
oxide domains over Ag nanoparticles, the plasmonic and superparamagnetic properties can be
combined in a single particle. Beyond the multifunctionality of this system, there are several
properties that emerge from intrinsic factors, such as: interface and/or morphology. In this study,
we present the synthesis protocols to obtain two sets of heterocrystals, each one with different
morphology: dimer and flower-like. In addition, the magnetization behavior of these hybrid
nano-heterocrystals is investigated and discussed. These nanomaterials were built by a seed
assisted heterogeneous nucleation process, carried out in organic solvents of high boiling point,
using the same batch of silver nanoparticles with a mean size of 6 nm as seeds, and tuning the
electron-donor capacity of the reaction environment at the thermal decomposition of the iron
precursor. Ag/Fe
3
O
4
heterocrystals with dimer and flower-like morphologies were obtained. The
synthesis protocols for generating these types of nanomaterials are discussed step-by-step.
Structural and morphological properties were determined by transmission electron microscopy
(TEM), X-ray diffraction (XRD) and X-ray absorption fine structure (XAFS). DC magnetization
results suggest that the silver/magnetite coupling generates an increase of the blocking
temperature in comparison to those obtained from pure magnetite. This behavior could be linked
to a possible increase in the magnetic anisotropy produced by an additional disorder at the Ag-
Fe
3
O
4
interface. The higher interface area of the Ag/Fe
3
O
4
heterocrystals with flower-like
architecture leads to a higher blocking temperature and a stronger magnetic anisotropy. These
results are supported by AC susceptibility data.
Keywords: hybrid nanostructures, interface effects, magnetic-plasmonic properties,
superparamagnetism.
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Introduction
In the last years, a prominent part of the research in nanochemistry has focused on the
preparation of multifunctional and heterostructured nanocrystals, capable of combining two or
more inorganic materials into a single system through a direct atomic bond at the interface and
without the presence of a molecular bridge [1-3]. In these new heterocrystals, the properties of
the different components can be combined or can give rise to new features associated to
morphology or interface effects, factors that may partially govern the physicochemical behavior
of these new kind of systems.
Nanoparticles that combine a noble metal (Au, Ag) with ferrite type oxides (Fe
3
O
4
, CoFe
2
O
4
,
Co
3
O
4
, MnFe
2
O
4
) are among the systems that have gained major interest. In these peculiar
nanostructures, the optical properties of metallic nanoparticles and the magnetic properties of Fe-
oxide counterparts can be coupled. This dual behavior opens the door to new applications in
several fields, including catalysis [4, 5], antimicrobial agents [6, 7], magnetic and
photo/magnetic hyperthermia therapies [8, 9] and surface-enhanced Raman scattering substrates
(SERS) [10], among others.
The most common process to produce heterostructured nanocrystals is the so-called seed-assisted
method, where a second component is heterogeneously nucleated over previously formed
nanoparticles (“seeds”) of a first component. In this process, the heterogeneous nucleation of the
second material is favored over homogeneous nucleation, especially when there is some
compatibility between the cell parameters of the crystals [10]. Depending on the nucleation
events and the growth evolution, the formed heterostructures can show distinct architectures,
such as core-shell, dimer or flower-like. Many efforts have been dedicated to the understanding
of the synthesis conditions and mechanisms that lead to these different morphologies [2, 11-13],
mainly because the macroscopic properties of the system can be controlled or tuned by the
interface type and the interactions between the different constituents.
In this work, we study the synthesis and the magnetic response of two Ag/Fe
3
O
4
heterostructures
with different morphologies: dimer and flower-like type, prepared by a seed-assisted route in
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organic solvents of high boiling point. In particular, we investigate how the solvent nature,
associated to its electron-donor capacity, determines the final morphology. Correspondingly, we
performed a complete magnetic characterization by means of DC and AC magnetization
techniques to understand how the heterostructures architecture and the distribution of the Fe
3
O
4
domains define the macroscopic behavior of the samples. A discussion on the structural and
optical properties is also presented to reinforce the results and the conclusions.
Experimental Details
Materials. Silver nitrate (AgNO
3
, ≥ 99%, Sigma-Aldrich), sodium acetate (NaCH
3
COO, ≥ 99%,
Anedra), oleylamine (C
17
H
31
-CH
2
NH
2
, ≥ 99%, Sigma-Aldrich), oleic acid (C
17
H
31
-COOH, 90%,
Sigma-Aldrich), 1-octadecene (C
18
H
36
, 90%, Sigma-Aldrich), diphenyl ether ((C
6
H
5
)
2
O, 98%,
Sigma-Aldrich), iron(III) acetylacetonate (Fe(acac)
3
, 99%, Sigma-Aldrich) and 1,2-
hexadecanediol (C
16
H
34
O
2
, 90%, Sigma-Aldrich). All chemicals were used as received without
further purification.
Methods. Ag/Fe
3
O
4
nanoparticles were synthesized by a seed assisted heterogeneous nucleation
process in organic solvents of high boiling point, as described below.
Silver Seeds Nanoparticles (AgNPs) synthesis: AgNPs were prepared according to previous
reports [8, 12]. Briefly, 2 mmol silver acetate (AgCH
3
COO) were obtained by stochiometric
precipitation of AgNO
3
and NaCH
3
COO. The so-obtained white powder was dissolved in 2
mmol oleic acid, 2 mmol oleylamine and 5 mL 1-octadecene. The mixture was heated up to 175
°C under continuous stirring for 30 min to allow AgNPs formation. Finally, the system was
cooled down to room temperature and the AgNPs were precipitated by the addition of ethanol
and isolated by centrifugation at 3000 RPM for 15 minutes. The isolated solid was washed 3
times before redispersed in hexane.
Ag/Fe
3
O
4
heteroparticles formation: AgNPs were used as fixed seeds for Fe
3
O
4
heterogeneous
nucleation. 1 mmol Ag (as AgNPs), 0.3 mmol Fe(acac)
3
, 1.5 mmol 1,2-hexadecanediol, 0.75
mmol oleic acid, 1.5 mmol oleylamine and 5 mL solvent (1-octadecene, ODE or phenyl ether,
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Citations
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Journal Article•DOI•
Magnetic and magneto-optical properties of Fe3O4 nanoparticles modified with Ag

[...]

D. A. Petrov, R. D. Ivantsov, Sergey M. Zharkov1, D. A. Velikanov1, Maxim S. Molokeev1, C.-R. Lin2, C.-T. Tso2, Hua-Shu Hsu2, Yaw-Teng Tseng2, En-Szu Lin2, Irina S. Edelman •
Siberian Federal University1, National Pingtung University2
01 Jan 2020-Journal of Magnetism and Magnetic Materials
TL;DR: In this paper, the effect of Ag inclusions on magnetic properties and magnetic circular dichroism (MCD) of Fe3O4 nanoparticles (NPs) in the mixed system of Fe 3O4 and Ag NPs in dependence on the relative concentration of the components is presented.

19 citations

Journal Article•DOI•
On the synthesis of bi-magnetic manganese ferrite-based core–shell nanoparticles

[...]

Marco Sanna Angotzi1, Valentina Mameli1, Claudio Cara1, Davide Peddis2, Huolin L. Xin3, Claudio Sangregorio4, Maria Laura Mercuri1, Carla Cannas1 •
University of Cagliari1, University of Genoa2, University of California, Irvine3, University of Florence4
23 Mar 2021
TL;DR: In this article, the formation mechanism of manganese ferrite-based core-shell NHSs is investigated, and the effects of the core size (8, 10, and 11 nm), the shell nature (cobalt ferrite and spinel iron oxide) and the polarity of the solvent (toluene and octanol) on the dissolution phenomena of nanocrystal materials are also studied.
Abstract: Multifunctional nano-heterostructures (NHSs) with controlled morphology are cardinal in many applications, but the understanding of the nanoscale colloidal chemistry is yet to be fulfilled. The stability of the involved crystalline phases in different solvents at mid- and high-temperatures and reaction kinetics considerably affect the nucleation and growth of the materials and their final architecture. The formation mechanism of manganese ferrite-based core–shell NHSs is herein investigated. The effects of the core size (8, 10, and 11 nm), the shell nature (cobalt ferrite and spinel iron oxide) and the polarity of the solvent (toluene and octanol) on the dissolution phenomena of manganese ferrite are also studied. Noteworthily, the combined use of bulk (powder X-ray diffraction, 57Fe Mossbauer spectroscopy, and DC magnetometry) and nanoscale techniques (HRTEM and STEM-EDX) provides new insights into the manganese ferrite dissolution phenomena, the colloidal stability in an organic environment, and the critical size below which dissolution is complete. Moreover, the dissolved manganese and iron ions react further, leading to an inverted core–shell in the mother liquor solution, paving the way to novel synthetic pathways in nanocrystal design. The MnFe2O4@CoFe2O4 core–shell heterostructures were also employed as heat mediators, exploiting the magnetic coupling between a hard (CoFe2O4) and a soft phase (MnFe2O4).

13 citations

Journal Article•DOI•
Defect-assisted synthesis of magneto-plasmonic silver-spinel ferrite heterostructures in a flower-like architecture.

[...]

Marco Sanna Angotzi1, Valentina Mameli1, Claudio Cara1, Vincenzo Grillo, Stefano Enzo2, Anna Maria Giovanna Musinu1, Carla Cannas1 •
University of Cagliari1, University of Sassari2
12 Oct 2020-Scientific Reports
TL;DR: An oleate-based solvothermal approach to design silver-spinel ferrite flower-like NHs with magnetic and optical properties that are suitable for a wide range of applications is proposed.
Abstract: Artificial nano-heterostructures (NHs) with controlled morphology, obtained by combining two or more components in several possible architectures, make them suitable for a wide range of applications. Here, we propose an oleate-based solvothermal approach to design silver-spinel ferrite flower-like NHs. Small oleate-coated silver nanoparticles were used as seeds for the growth of magnetic spinel ferrite (cobalt ferrite and spinel iron oxide) nanodomains on their surface. With the aim of producing homogeneous flower-like heterostructures, a careful study of the effect of the concentration of precursors, the reaction temperature, the presence of water, and the chemical nature of the spinel ferrite was carried out. The magnetic and optical properties of the NHs were also investigated. A heterogeneous growth of the spinel ferrite phase on the silver nanoparticles, through a possible defect-assisted mechanism, was suggested in the light of the high concentration of stacking faults (intrinsic and twins) in the silver seeds, revealed by Rietveld refinement of powder X-ray diffraction patterns and High-Resolution electron microscopy.

8 citations

Book Chapter•DOI•
Magneto-Plasmonic Nanoparticles

[...]

César de Julián Fernández, Francesco Pineider1•
University of Pisa1
01 Jan 2021
TL;DR: Magnetoplasmonic nanoparticles encompass in a single nano-entity all the rich science and promising applications of the plasmonics and magnetic nanoworlds as discussed by the authors, and they are excellent benchmark materials to develop and investigate multiresponsive multifunctional nanosystems that now are required in an increasing number of technologies, such as biomedicine, pharmacy, catalysis, optoelectronics and data storage.
Abstract: Magnetoplasmonics nanoparticles encompass in a single nano-entity all the rich science and promising applications of the plasmonics and magnetic nanoworlds. The difficult liaison and a certain incompatibility between plasmonics and magnetic phenomena, due to the different chemical-physical origins and supporting materials, are overcome thanks to the design and synthesis of novel nanostructures. The variations of properties, interactions and synergies of both phenomena and materials demonstrate how rich and surprising the matter is at nanoscale and the promising applications. In fact, we show how not only light and magnetism can interplay but also other phenomena like forces, heat, electric field and chemical interactions, between others, can show synergism. Magnetoplasmonic systems are excellent benchmark materials to develop and investigate multi-responsive multifunctional nanosystems that now are required in an increasing number of technologies, such as biomedicine, pharmacy, catalysis, optoelectronics and data storage.

4 citations

Journal Article•DOI•
Synthetic Approaches to Colloidal Nanocrystal Heterostructures Based on Metal and Metal-Oxide Materials

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Concetta Nobile, P. Davide Cozzoli
01 May 2022-Nanomaterials
TL;DR: In this article , a critical overview of achievements made in the design and synthetic elaboration of colloidal nanocrystal heterostructures based on diverse associations of transition metals (with emphasis on plasmonic metals) and transition-metal oxides is presented.
Abstract: Composite inorganic nanoarchitectures, based on combinations of distinct materials, represent advanced solid-state constructs, where coexistence and synergistic interactions among nonhomologous optical, magnetic, chemical, and catalytic properties lay a basis for the engineering of enhanced or even unconventional functionalities. Such systems thus hold relevance for both theoretical and applied nanotechnology-based research in diverse areas, spanning optics, electronics, energy management, (photo)catalysis, biomedicine, and environmental remediation. Wet-chemical colloidal synthetic techniques have now been refined to the point of allowing the fabrication of solution free-standing and easily processable multicomponent nanocrystals with sophisticated modular heterostructure, built upon a programmed spatial distribution of the crystal phase, composition, and anchored surface moieties. Such last-generation breeds of nanocrystals are thus composed of nanoscale domains of different materials, assembled controllably into core/shell or heteromer-type configurations through bonding epitaxial heterojunctions. This review offers a critical overview of achievements made in the design and synthetic elaboration of colloidal nanocrystal heterostructures based on diverse associations of transition metals (with emphasis on plasmonic metals) and transition-metal oxides. Synthetic strategies, all leveraging on the basic seed-mediated approach, are described and discussed with reference to the most credited mechanisms underpinning regioselective heteroepitaxial deposition. The unique properties and advanced applications allowed by such brand-new nanomaterials are also mentioned.

3 citations

References
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Journal Article•DOI•
Seeded Growth Synthesis of Au–Fe3O4 Heterostructured Nanocrystals: Rational Design and Mechanistic Insights

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Elvira Fantechi1, Alejandro G. Roca1, Borja Sepúlveda1, Pau Torruella2, Sònia Estradé2, Francesca Peiró2, Emerson Coy, Stefan Jurga, Neus G. Bastús1, Josep Nogués1, Víctor F. Puntes1 •
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60 citations

Journal Article•DOI•
Magnetic, optical and relaxometric properties of organically coated gold–magnetite (Au–Fe3O4) hybrid nanoparticles for potential use in biomedical applications

[...]

E. Umut1, Francesco Pineider2, Paolo Arosio3, Claudio Sangregorio2, Maurizio Corti, F. Tabak1, Alessandro Lascialfari3, Paolo Ghigna •
Hacettepe University1, University of Florence2, University of Milan3
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TL;DR: In this article, the magnetic, optical and relaxometric properties of multifunctional Au-Fe 3 O 4 hybrid nanoparticles (HNPs) were investigated for magnetic resonance imaging (MRI) applications.

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Journal Article•DOI•
Crystal engineering and SERS properties of Ag–Fe3O4 nanohybrids: from heterodimer to core–shell nanostructures

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Jianmei Huang1, Yanhui Sun2, Shoushuang Huang1, Kang Yu1, Qing Zhao2, Feng Peng1, Hao Yu1, Hongjuan Wang1, Jian Yang3, Jian Yang1 •
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TL;DR: In this article, a family of Ag-Fe3O4 nanohybrids is synthesized via a simple one-step reaction of silver acetate and iron acetylacetonate in the presence of 1,2-dodecanediol, oleylamine and oleic acid.
Abstract: Structure tailoring of hybrid nanoparticles is highly desirable for a number of applications, due to their controllable physical properties. Here, a family of Ag–Fe3O4 nanohybrids is synthesized via a simple one-step reaction of silver acetate and iron acetylacetonate in the presence of 1,2-dodecanediol, oleylamine and oleic acid. The as-obtained Ag–Fe3O4 nanohybrid could be finely tuned from heterodimer nanoparticles to flower-like or core–shell nanoparticles, by controlling the experimental conditions. The structural differences between these nanohybrids greatly affect their optical properties. The intense surface plasmon resonance (SPR) peak allows the heterodimer nanoparticles to act as a superior surface-enhanced Raman scattering (SERS) substrate, which has been demonstrated by using 2-naphthalenethiol as a probe molecule. It is noted that the SERS signal of 2-naphthalenethiol on the heterodimer nanoparticles is much stronger than those on the core–shell nanohybrid and Ag nanoparticles alone, indicating its potential in the fields of ultrasensitive detection and biological imaging.

58 citations

Journal Article•DOI•
Compact Ag@Fe3O4 core-shell nanoparticles by means of single-step thermal decomposition reaction.

[...]

Maria Eugênia Fortes Brollo1, R. López-Ruiz1, Diego Muraca1, Santiago J. A. Figueroa, Kleber R. Pirota1, Marcelo Knobel1 •
State University of Campinas1
01 May 2015-Scientific Reports
TL;DR: A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles that indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature.
Abstract: A temperature pause introduced in a simple single-step thermal decomposition of iron, with the presence of silver seeds formed in the same reaction mixture, gives rise to novel compact heterostructures: brick-like Ag@Fe3O4 core-shell nanoparticles. This novel method is relatively easy to implement, and could contribute to overcome the challenge of obtaining a multifunctional heteroparticle in which a noble metal is surrounded by magnetite. Structural analyses of the samples show 4 nm silver nanoparticles wrapped within compact cubic external structures of Fe oxide, with curious rectangular shape. The magnetic properties indicate a near superparamagnetic like behavior with a weak hysteresis at room temperature. The value of the anisotropy involved makes these particles candidates to potential applications in nanomedicine.

56 citations

Journal Article•DOI•
Magnetic hyperthermia in brick-like Ag@Fe3O4 core–shell nanoparticles

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Maria Eugênia Fortes Brollo1, J. M. Orozco-Henao1, R. López-Ruiz1, Diego Muraca1, Carlos S. B. Dias1, Kleber R. Pirota1, Marcelo Knobel1 •
State University of Campinas1
01 Jan 2016-Journal of Magnetism and Magnetic Materials
TL;DR: In this article, specific absorption rate (SAR) measurements were carried out by using the superparamagnetic theory, in which the basic morphology, size and dispersion of sizes played key roles.

56 citations

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Frequently Asked Questions (1)
Q1. What contributions have the authors mentioned in the paper "Strategies to tailor the architecture of dual ag/fe-oxide nano- heterocrystals - interfacial and morphology effects on the magnetic behavior" ?

Particularly, by growing Feoxide domains over Ag nanoparticles, the plasmonic and superparamagnetic properties can be combined in a single particle. In this study, the authors present the synthesis protocols to obtain two sets of heterocrystals, each one with different morphology: dimer and flower-like. These nanomaterials were built by a seed assisted heterogeneous nucleation process, carried out in organic solvents of high boiling point, using the same batch of silver nanoparticles with a mean size of 6 nm as seeds, and tuning the electron-donor capacity of the reaction environment at the thermal decomposition of the iron precursor. The synthesis protocols for generating these types of nanomaterials are discussed step-by-step. DC magnetization results suggest that the silver/magnetite coupling generates an increase of the blocking temperature in comparison to those obtained from pure magnetite.