Solid State Communications 191 (2014) 14–18
Contents lists available at ScienceDirect
Solid State Communications
journal homepage: www.elsevier.com/locate/ssc
Exploring the effects of dimensionality on the magnetic properties
of intermetallic nanowires
P.F.S. Rosa a,n,1, L.A.S. de Oliveira a, C.B.R. de Jesus a, K.O. Moura a, C. Adriano a,
W. Iwamoto a,b, T.M. Garitezi a, E. Granado a,c, M.E. Saleta a,c, K.R. Pirota a, P.G. Pagliuso a
a
Instituto de Física “Gleb Wataghin”, UNICAMP, Campinas-SP 13083-859, Brazil
Instituto de Física, Universidade Federal de Uberlândia, 38400-902, Uberlândia-MG, Brazil
c
Laboratório Nacional de Luz Síncrotron, Caixa Postal 6192, CEP 13084-971, Campinas, SP, Brazil
b
art ic l e i nf o
a b s t r a c t
Article history:
Received 16 March 2014
Accepted 19 April 2014
by A.H. MacDonald
Available online 28 April 2014
Correlated electron intermetallic bulk systems exhibit exciting phenomena, such as unconventional
superconductivity, heavy fermion behavior, magnetic ordering, and quantum criticality. However,
such exciting properties in related systems with reduced dimensionality are rather unexplored and
unpredictable. In this work, we explore the routes for synthesizing nanowires of the intermetallic
antiferromagnet compound GdIn3 by an innovative method: the metallic-flux nanonucleation (MFNN).
This technique allows the simultaneous synthesis of bulk GdIn3 single crystals ðT 3D
N ¼ 45 KÞ and their
low-dimensional (LD) analogs, which nucleate with diameter d 200 nm and length l 30 μm inside
pores of an Al2O3 template. Both systems were studied by means of Energy Dispersive Spectroscopy
(EDS), magnetic susceptibility, heat capacity and electron spin resonance (ESR) measurements. Interestingly, the metallic nanowires show a drastic suppression of the antiferromagnetic ordering to
T LD
N ¼ 4 K. These observations suggest the presence of LD magnetic frustration in this compound and
possibly open a new route to explore the role of low-dimensionality in strongly correlated materials.
& 2014 Elsevier Ltd. All rights reserved.
Keywords:
A. Intermetallic compounds
B. Low dimensionality
D. RKKY interaction
1. Introduction
In general, interacting many-body systems obey the symmetry
properties of periodic lattices when the particles are confined
within a crystalline solid [1]. The microscopic description of these
systems relies on the existence of translational symmetry in three
dimensions, which allows Bloch's theorem to apply, leading to the
formation of valence/conduction bands. Furthermore, it is desirable to understand the properties of interacting condensed-matter
systems by unveiling spontaneous symmetry breaking, such as
magnetic and crystalline orderings, superfluidity and superconductivity; elementary excitations, such as quasiparticles in heavy
fermion systems; collective modes such as plasmons; and phase
transitions [2]. In all cases, the system dimensionality and the
disruption of translation symmetry, when one of the solid dimensions becomes comparable to the important length scale of the
problem, plays a fundamental and unpredictable role in determining the system ground state. Moreover, in reduced spatial
n
Corresponding author. Tel.: þ 55 65 35215501.
E-mail addresses: ferrari@ifi.unicamp.br, pfsrosa@uci.edu (P.F.S. Rosa).
1
Present address: University of California at Irvine. Tel.: þ 1 949 9240443.
http://dx.doi.org/10.1016/j.ssc.2014.04.013
0038-1098/& 2014 Elsevier Ltd. All rights reserved.
dimensions, many-body correlation effects due to the Coulomb
interaction between electrons tend to become more relevant.
In particular, the series Rm M n In3m þ 2n (R¼ rare-earth, M¼ Co,
Rh, Ir; n¼0, 1; m¼ 1, 2) of intermetallic compounds would be
a fantastic system to study in low dimensions since they have
several remarkable physical properties such as complex magnetic
ordering, Ruderman–Kittel–Kasuya–Yoshida (RKKY) magnetic interaction, crystalline electrical field (CEF), Fermi surface (FS) effects
and, for R¼ Ce, non-Fermi-liquid behavior, quantum criticality (QC)
and the interplay between antiferromagnetism and unconventional
superconductivity (USC) [3–5]. This variety of interesting physical
properties in structurally related series represents a great opportunity to explore systematically the role of the each interaction in
determining the system properties, specially in favoring USC in
many Ce-based members of these series. As the properties of the
heavy-fermion superconductors in their family are presumably
magnetically mediated, the study of non-Kondo isostructural
Rm M n In3m þ 2n (R¼ Nd, Gd, Tb) magnetic materials has been used
to elucidate the role of the RKKY interactions and CEF effects in the
evolution of the magnetic properties [6–10].
The cubic intermetallic compound GdIn3 [11] is a promising
candidate to start a new route to study LD systems since it allows
one to individually investigate the dimensionality effects on the
P.F.S. Rosa et al. / Solid State Communications 191 (2014) 14–18
RKKY magnetic interaction, i.e. the intersite exchange interaction
mediated by the conduction electrons (ce). In fact, it has been
already shown by resonant X-ray magnetic diffraction that the
GdIn3 antiferromagnetic (AFM) ordering temperature (TN) has a
dependence with the X-ray penetration depth, displaying a larger
TN in the surface as compared to the bulk [12]. By making use of
macroscopic measurements, such as magnetic susceptibility and
heat capacity, one can study the evolution of the bulk AFM order
at T 3D
N ¼ 45 K with the dimensionality. Additionally, electron spin
resonance (ESR) is a highly sensitive microscopic technique that
has been used to investigate spin fluctuations and magnetic interactions in such compounds. In particular, CEF effect is a higher
order effect in the Gd3 þ S-state (S ¼7/2, L ¼0) ground state. As
such, Gd ions are excellent ESR probes to study magnetic properties which purely reflect the details of RKKY magnetic interaction
and FS effects in intermetallic magnetic materials. Thus, ESR
experiments can reveal details about the microscopic interaction
Jfs between the 4f electrons and the ce.
However, the growth of intermetallic nanowires containing a
rare-earth element has been challenging [13–18]. In the present
work we have successfully synthesized Gd-In nanowires close to
1:3 ratio by an innovative method called metallic-flux nanonucleation (MFNN). Our results show a drastic suppression of the
antiferromagnetic transition from the bulk ðT 3D
N ¼ 45 KÞ to the
15
nanowire system ðT LD
N ¼ 3:8 KÞ which we speculated to be due to
a change in the magnetic RKKY exchange interaction. These
observations indicate the presence of magnetic frustration driven
by low-dimensionality in this compound and may open a new
field for the research of the role of low-dimensionality in strongly
correlated materials.
2. Experiment
Intermetallic nanowires with 1Gd:3In stoichiometry were successfully grown by the metallic flux nanonucleation (MFNM)
method. This innovative method is based on the conventional
flux-growth technique [19] performed in a nanometric template
that mediates the preferential nucleation of the single crystals
in the desired geometry [20]. Particularly, in this work we have
used Al2O3 membranes fabricated via hard anodization process,
described in detail in Ref. [21]. The difference between MFNN
method and the classical flux-growth technique is the presence of
this anodized Al2O3 membrane fixed in the base of an alumina
crucible enclosing the involved metals. The metals were weighted
in the ratio 1 Gd to 10 In. The crucible containing the elements and
the membrane was covered with quartz wool and sealed inside
an evacuated quartz tube. The tube was placed in a furnace and
Fig. 1. (Color online) Scanning electron microscope (FE-SEM) image and Energy Dispersive X-Ray Spectroscopy (EDS) mapping of GdIn3 nanowires. (a) FE-SEM image of
GdIn3 nanowires grown by the innovative MFNN method, (b) SEM image of a GdIn3 nanowire, and EDS composition mapping for (c) Gd Lα and (d) In Lα.
16
P.F.S. Rosa et al. / Solid State Communications 191 (2014) 14–18
heated up to 1100 1C with a rate of 50 1C/h. After 8 h at 1100 1C, the
batch was subjected to a slow cooling rate of 2 1C/h down to
650 1C. The excess In flux was then spun in a centrifuge and the
membrane with the GdIn3 nanowires was mechanically removed
from the crucible. This method yields a simultaneous synthesis of
bulk single crystals and nanowires extracted from flux growth.
Therefore, any intermetallic compound that can be prepared by
flux-growth method, in principle, could also be synthesized in
nanowire form by the MFNN method.
Bulk and nanowire of the Gd3 þ systems were analyzed at a
commercial FEI Inspect F-50 Field Emission Scanning Electron
Microscope (FE-SEM) and submitted to elemental analysis using a
commercial Energy Dispersive X-Ray Spectroscopy (EDS) microprobe. Specific heat data were taken in a commercial Quantum
Design PPMS-14T small-mass calorimeter and the magnetization
data were collected using a superconducting quantum interference
device (SQUID) magnetometer MPMS-7T from Quantum Design.
X-Band (ν ¼9.5 GHz) ESR measurements were performed in a
commercial Bruker spectrometer with a continuous He gas-flow
cryostat. Experiments of high intensity X-ray diffraction were also
performed on the membrane containing the Gd-In nanowires. The
data were collected at XDS beamline (LNLS - Campinas-SP, Brazil)
at 20 keV. Unfortunately these data are dominated by the presence
of the diffraction pattern of the Al2O3 and turned out to be
inconclusive regarding the presence of GdIn3 crystalline pattern.
Therefore, further structural characterization becomes crucial to
confirm the crystallinity of the obtained nanowires. Challenging
experiments of electron diffraction on individual nanowires will
help us to clarify this issue.
3. Results and discussion
Fig. 1a displays the high resolution scanning electron microscope (FE-SEM) image, which evidence the growth of nanowires
with diameter of 200 nm and length of 30 μm. Panel (1b)
shows a magnified view of a nanowire and panels (1c) and (1d)
show its composition given by Energy Dispersive X-ray Spectrometry (EDS) mapping. It is clear that both Gd and In are present
and the EDS spectra gives roughly the same proportionality
between Gd and In in both bulk and nanowire systems.
Now we turn our attention to the role of dimensionality on
the physical properties of both GdIn3 systems. Fig. 2a shows the
magnetic susceptibility as a function of temperature, χ(T), for
H ¼1 kOe. We observe a drastic suppression of the antiferromagnetic ordering temperature from T bulk
¼ 45 K (inset red arrow)
N
to T nano
¼
3:8
K
(inset
black
arrow).
For
both
bulk and LD systems,
N
χ(T) for T 4 T N can be fitted to a Curie–Weiss law plus a
T-independent Pauli term, χ(T)¼ χ0 þ C/ðT θCW Þ (solid lines).
Table 1 displays the fitted parameters. The effective moment (peff)
for the Gd3 þ ions, extracted from the Curie–Weiss constant (C),
is in agreement with the theoretical value ptheory
¼ 7:94 μB , as
eff
expected. Furthermore, jθCW j 4 T N for both systems, indicating the
existence of magnetic frustration as previously reported [22–24].
Interestingly, the ratio θCW =T N is larger for the LD system,
suggesting that the frustration is stronger in the nanowire than
in the bulk system. However, the main effect revealed by our data
is the huge suppression of θCW by a factor of 8 in the nanowire
system in comparison with the bulk system. In a molecular field
approximation, this result strongly indicates that the effective
exchange interaction between the Gd3 þ moments is dramatically
reduced in the Gd-In nanowires.
The AFM transition can also be clearly observed in the specific
heat data, shown in Fig. 2b. The sharp peaks in C/T corresponding
to the onset of the AFM order can be seen at 45 K for the bulk
compound and at 3.8 K for the nanowire compound, in very good
Fig. 2. (Color online) Physical properties of GdIn3 bulk and nanowire systems.
(a) Temperature dependence of the magnetic susceptibility taken with applied
field H¼ 1 kOe and (b) specific heat divided by temperature as a function of
temperature.
Table 1
Fitted parameters for both bulk and nanowire GdIn3 systems of a Curie–Weiss law
plus a T-independent Pauli term, χ(T) ¼χ0 þ C/ðT θCW Þ.
GdIn3
θCW ðKÞ
χ0 (emu/mol.Oe)
peff ðμB Þ
θCW =T N
Bulk
Nanowire
91
12
3 10 3
1 10 3
7.9
7.2
2.0
3.2
agreement with the maximum in the magnetic susceptibility
derivative (see Fig. 2a). The estimated magnetic entropy recovered
at TN roughly reaches the value of R.ln(8) expected for the whole
Gd3 þ S¼ 7/2 (not shown). However, the data at high temperatures
should be taken with care. Ongoing studies in the non-magnetic
compound LaIn3 will shed light on the phononic contribution in
this system.
In order to microscopically probe the magnetic system, we now
turn our attention to the electron spin resonance (ESR) data in
which a single Gd3 þ ESR resonance emerges for both systems.
Fig. 3 shows the X-Band ðν 9:5 GHzÞ ESR lines at T ¼300 K. For
the bulk system, ESR lines are isotropic and have an asymmetric
Dysonian character, characteristic of samples in which the skin
depth (δ ¼2 μm at room-T) is smaller than the sample dimension
[26]. At room temperature we found a Gd3 þ ESR linewidth ΔH ¼
1:3ð1Þ kG and a g-value g¼1.9(1). On the other hand, the nanowire
system clearly displays a symmetric (Lorentzian) character, consistent with the fact that in this case the sample size ð 200 nmÞ is
P.F.S. Rosa et al. / Solid State Communications 191 (2014) 14–18
Fig. 3. (Color online) Electron spin resonance (ESR) lineshapes for both bulk and
nanowire systems. X-Band (ν ¼ 9.5 GHz) ESR lines at T ¼ 300 K for both bulk and
nanowire systems.
Fig. 4. (Color online) Electron spin resonance (ESR) fitted parameters as a function
of temperature. Temperature dependence of the ESR linewidth ΔH for both bulk
and nanowire systems. The error bars are estimated as 10% of the linewidth. The
inset displays the g-value and the ESR intensity as a function of temperature for the
LD system.
much smaller than the skin depth. In addition, the ESR linewidth is
slightly larger for the nanowire compound, ΔH ¼ 2:2ð2Þ kG. We
speculate that the presence of higher level of strain in the
nanowires may generate an inhomogeous contribution to the
ESR linewidth [27,28].
From the fits of the ESR lineshapes using the appropriate
admixture of absorption and dispersion (solid lines in Fig. 3), we
obtained the temperature dependences of both ΔH and g-value,
shown in Fig. 4. In the bulk system, we observe an isotropic linear
(Korringa-like, [29]) increase of the ΔH with increasing temperature for T≳T N . From linear fits to ΔHðTÞ we extracted the Korringa
rate b ¼ dðΔHÞ=dT ¼ 3:0ð5Þ Oe/K. On the other hand, there is no
Korringa behavior in the nanowire system.
At temperatures T≳T 3D
N , the nanowire ΔH is strongly broadened due to the development of reminiscent short range AFM
correlations. Consistently, the g-factor starts to decrease (i.e., the
resonance field increases) indicating an AFM internal field (see
inset of Fig. 4.). We note that these correlations define how the
distribution of local fields decrease as the long range ordered state
starts to develop. They are responsible for the subtle linewidth
decrease below 50 K. However, long range AFM order cannot be
fully established, presumably due to the above-mentioned
17
magnetic frustration. Interestingly, ferromagnetic fluctuations
start to emerge below 50 K inducing a g-factor increase (smaller
resonance field) due to a ferromagnetic (FM) local field contribution. Such positive g-shift may be associated with ferromagnetic
(FM) stripes present in the magnetic structure of GdIn3. The AFM
spin structure in the bulk system has a propagation vector
Q¼ (1/2, 1/2, 0), corresponding to a parallel spin propagation along
the c direction and antiparallel propagation along a and b [12]. We
speculate that this FM stripe-like magnetic interaction may be
enhanced in nanowires and, thus, it contributes to the suppression
of the 3D effective magnetic exchange interactions responsible for
long range AFM ordering. This FM interaction may also generate
short-range FM-like interactions in the paramagnetic state that, in
turn, can be responsible for dipolar–dipolar interactions between
nanowires. An inhomogeneous distribution of dipolar interactions
between the nanowires may also explain the broader Gd3 þ ESR
linewidth in the LD system. Finally, the inset of Fig. 4 displays the
T-dependence of both Gd3 þ ESR g-value (left) and ESR intensity
(right). The latter scales with the Curie law for T 4 50 K, indicating
that the same local moments which contribute to the magnetic
susceptibility are contributing to the ESR resonance. The g-factor
shows a constant value at high temperatures g 1:9ð1Þ, as in
the bulk.
Therefore, the drastic suppression of the RKKY-mediated antiferromagnetic order suggests that the exchange interaction JfsS.s
between the localized Gd3 þ 4f electron spin (S) and the free ce
spins (s) (and/or the density of states at the Fermi level of the host
metal) does not remain the same. This also implies that there is
a characteristic length-scale larger than the nanowire diameter
ð 200 nmÞ. In fact, resonant X-ray diffraction on GdRhIn5 much
below TN [8] indicates long-range order with correlation length
above 500 nm. Interestingly, the AFM order is fully suppressed
in CeIn3 thin films [25].
Moreover, the ESR data agree with this suppression of Jfs. It is
essential to notice that the Korringa rate b ¼ ðPk=g μB ÞJ 2fs η2 ðEF Þ and
also the characteristic temperature for the RKKY interaction,
T RKKY p J 2fs NðEF Þ2 have the same dependence on product of the
exchange interaction, Jfs, and the density of states at the Fermi
level, NðEF Þ. Therefore, the suppression of the antiferromagnetic
order temperature should be reflected also in a further suppression of the Korringa rate. In fact, it is evident from Fig. 4 that the
Korringa mechanism is indeed suppressed in the nanowire compound. This result is in agreement with the Korringa rate suppression in rare-earth doped metallic nanoparticles [30]. In these
cases, the spin–spin interactions dominate (the linewidth is now
due to the spin–spin relaxation time, T2) and broadens the line as
the temperature is decreased. However, a systematic study of a
series of GdIn3 nanowires with distinct diameters will be valuable
to confirm such results. We are currently employing our MFNN
method to grow nanowires with much smaller diameters.
4. Conclusions
In summary, we employed an innovative growth method to
synthesize 1Gd:3In nanowires. We observe macro and microscopically a drastic suppression of the antiferromagnetic transition
LD
from the bulk ðT 3D
N ¼ 45 KÞ to the nanowire system ðT N ¼ 3:8 KÞ
which may be associated to a change in the magnetic RKKY
exchange interaction. These observations suggest a possible lowdimensional magnetic frustration in this compound and possibly
open a new field for the research of the role of low-dimensionality
in strongly correlated materials. In fact, ongoing studies will help
us confirm our claim in other members of the R In3 (R ¼ Ce, Nd)
family. For instance, in the CeIn3 member, TN was suppressed from
10 K in the bulk system to 3 K in the nanowires. In the case
18
P.F.S. Rosa et al. / Solid State Communications 191 (2014) 14–18
of NdIn3, no AFM transition was observed down to 2 K for the
nanowires while TN is 6 K in the bulk system. However, the
macroscopic interpretation of the AFM suppression in these
members must take into account the evolution of the crystal field
and Kondo effects as a function of dimensionality. This will require
a more complete and detailed analysis of the data and will be the
scope of a separate report.
[8]
[9]
[10]
[11]
[12]
[13]
[14]
Acknowledgments
This work was supported by FAPESP (in particular grants No
2006/60440-0, 2009/09247-3, 2010/11949-3, 2010/09545-1, 2011/
12292-0, 2011/01564-0, 2011/23650-5, 2012/04870-7, 2013/17427-7),
CNPq, FINEP-Brazil. The authors would like to acknowledge the
Brazilian Nanotechnology National Laboratory (LNNano – Project
Inspect-14958) for providing the equipment and technical support
for the experiments involving scanning electron microscopy.
[15]
[16]
[17]
[18]
[19]
[20]
[21]
[22]
[23]
[24]
References
[1] N.W. Ashcroft, N.D. Mermin, Solid State Physics, Saunders College, Philadelphia,
PA, 1976.
[2] F.A.L. Fetter, J.D. Walecka, Quantum Theory of Many- Particle Systems, Dover
Publications, Inc., Mineola, New York, 2003.
[3] F. Steglich, et al., Phys. Rev. Lett. 43 (1979) 1892;
C. Petrovic, et al., J. Phys.: Condens. Matter 13 (2001) L337;
M. Rotter, M. Tegel, D. Johrendt, Phys. Rev. Lett. 101 (2008) 107006;
Y. Kamihara, et al., J. Am. Chem. Soc. 130 (11) (2008).
[4] K. Andres, J.E. Graebner, H.R. Ott, Phys. Rev. Lett. 35 (1975) 1779–1782.
[5] J. Custers, et al., Nature 424 (2003) 524–527.
[6] P.G. Pagliuso, et al., J. Appl. Phys. 99 (2006) 08P703.
[7] E. Granado, et al., Phys. Rev. B 69 (2004) 144411.
[25]
[26]
[27]
[28]
[29]
[30]
E. Granado, et al., Phys. Rev. B 74 (2006) 214428.
R. Lora-Serrano, et al., Phys. Rev. B 74 (2006) 214404.
J.G.S. Duque, et al., J. Appl. Phys. 103 (2008) 07B733.
Ya.M. Kalychak, J. Alloys Compd. 291 (1999) 80.
A. Malachias, E. Granado, R. Lora-Serrano, P.G. Pagliuso, C.A. Pérez, Phys. Rev. B
77 (2008) 094425.
J. Nogami, B.Z. Liu, M.V. Katkov, N.O. Birge, C. Ohbuchi, Phys. Rev. B 63 (2001)
233305;
Y. Chen, D.A.A. Ohlberg, R.S. Williams, J. Appl. Phys. 91 (2002) 3213.
R. Mishra, Electrodeposition of Rare Earth-transition Metal Alloy Thin Films
and Nanostructures, Department of Chemical Engineering. Louisiana State
University, USA. May, 2007.
X. Wang, J. Zhuang, Q. Peng, Y. Li, Nature 437 (2005) 121–124.
Y. Mao, F. Zhang, S.S. Wong, Adv. Mater. 18 (July 14) (2006) 1895–1899.
H. Zhang, Q. Zhang, J. Tang, L. Qin, J. Am. Chem. Soc. 127 (2005) 8002–8003.
H. Mai, et al., J. Am. Chem. Soc. 128 (19) (2006) 6426–6436.
Z. Fisk, J.P. Remeika, Growth of single crystals from molten metal fluxes,
vol. 12. Elsevier Science Publishers, chapter 81 edition, 1989.
H. Masuda, K. Fukuda, Science 268 (1995) 1466–1468.
W. Lee, R. Ji, U. Gosele, K. Nielsch, Nat. Mater. 5 (2006) 741–747.
H. Nakamura, K. Ito, H. Wada, M. Shiga, Physica B 186 (1993) 633–635.
P.G. Pagliuso, J.D. Thompson, M.F. Hundley, J.L. Sarrao, Z. Fisk, Phys. Rev. B 63
(2001) 054426.
K. Gofryk, D. Kaczorowski, K.T. Plackowski, A. Leihe-Jasper, Yu. Grin, Magnetic
and transport properties of rare-earth based Heusler phases RE PdX and REPd2 X
(X¼ Sb, Bi), in: Proceedings of 2nd European Conference on Thermoelectrics of
European Thermoelectric Society, Poland, Kraków, September 15–17, 2004.
H. Shishido, et al., Science 327 (5968) (2010) 980–983.
F.J. Dyson, Phys. Rev. 98 (1955) 349.
H.S. Shin, J. Yu, J.Y. Song, H.M. Park, Appl. Phys. Lett. 94 (2009) 011906.
Future multiple bands ESR experiments will be performed to confirm this
speculation.
The Korringa parameter b represents the thermal broadening rate of the ESR
line which is proportional to the relaxation rate (1/T1, where T1 is the spinlattice relaxation time) of the Gd3 þ resonating spins via ce electrons and
ultimately to the lattice. See Korringa, J. Physica 16, 601 (1950) and references
therein.
J.M. Vargas, et al., J. Nanosci. Nanotechnol. 11 (3) (2011) 2126–2131.