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
Accepted Manuscript is “the version of the article accepted for publication including all changes made as a result of the peer review process,
and which may also include the addition to the article by IOP Publishing of a header, an article ID, a cover sheet and/or an ‘Accepted
Manuscript’ watermark, but excluding any other editing, typesetting or other changes made by IOP Publishing and/or its licensors”
This Accepted Manuscript is © 2018 IOP Publishing Ltd.
During the embargo period (the 12 month period from the publication of the Version of Record of this article), the Accepted Manuscript is fully
protected by copyright and cannot be reused or reposted elsewhere.
As the Version of Record of this article is going to be / has been published on a subscription basis, this Accepted Manuscript is available for reuse
under a CC BY-NC-ND 3.0 licence after the 12 month embargo period.
After the embargo period, everyone is permitted to use copy and redistribute this article for non-commercial purposes only, provided that they
adhere to all the terms of the licence https://creativecommons.org/licences/by-nc-nd/3.0
Although reasonable endeavours have been taken to obtain all necessary permissions from third parties to include their copyrighted content
within this article, their full citation and copyright line may not be present in this Accepted Manuscript version. Before using any content from this
article, please refer to the Version of Record on IOPscience once published for full citation and copyright details, as permissions will likely be
required. All third party content is fully copyright protected, unless specifically stated otherwise in the figure caption in the Version of Record.
View the article online for updates and enhancements.
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
Page 1 of 26 AUTHOR SUBMITTED MANUSCRIPT - JPhysD-116701.R2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Accepted Manuscript
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.
Page 2 of 26AUTHOR SUBMITTED MANUSCRIPT - JPhysD-116701.R2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Accepted Manuscript
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
Page 3 of 26 AUTHOR SUBMITTED MANUSCRIPT - JPhysD-116701.R2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Accepted Manuscript
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,
Page 4 of 26AUTHOR SUBMITTED MANUSCRIPT - JPhysD-116701.R2
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
Accepted Manuscript