Post on 22-Apr-2023
RESEARCH PAPER
Magnetic configurations of Ni–Cu alloy nanowires obtainedby the template method
Elena Matei • Ionut Enculescu •
Maria Eugenia Toimil-Molares • Aurel Leca •
Corneliu Ghica • Victor Kuncser
Received: 25 February 2013 / Accepted: 12 July 2013
� Springer Science+Business Media Dordrecht 2013
Abstract High aspect ratio nanowires of Ni–Cu
alloys have been synthesized by potentiostatic elec-
trochemical deposition in etched ion-track mem-
branes. The nickel-to-copper ratio in the nanowires
was controlled via the deposition potential and elec-
trochemical bath composition. We present a detailed
study of nanowire properties including morphology,
composition, and magnetic behavior. We report the
magnetic configurations measured as function of the
nanowire composition and discuss domain formation,
anisotropy aspects, and local easy axis distributions.
Keywords Ni–Cu magnetic nanowires �Flower-like spin structure � Switching field �Magnetic structure
Introduction
Nanowires with controlled dimension and composition
constitute unique model systems to investigate the
magnetic properties of one-dimensional systems.
Among the various methods available to synthesize
magnetic nanowires, (e.g., lithographic techniques,
chemical reduction, and hydrothermal method) the
template approach is frequently employed, and allows a
simultaneous and precise control on both morphology
and composition. With this method, the pores of a
certain template are filled with the material of interest.
Usually, anodic porous alumina (Sugawara et al. 1998),
molecular sieves (Ozin 1992), or ion-track membranes
(Martin 1994; Fert and Piraux 1999; Yi and Schwarz-
acher 1999; Toimil Molares et al. 2001; Ohgai et al.
2003; Matei et al. 2010) are used as templates. In
particular, the electrochemical deposition in etched ion-
track membranes provides an excellent and independent
control on nanowire dimensions (length and diameter)
and wire density. Arrays of magnetic nanowires of
materials, such as Co, Ni, and Fe have been synthesized,
mostly by electrochemical deposition, as well as more
complex multilayered nanowires exhibiting giant mag-
netoresistance effect in a current perpendicular to plane
geometry (Gravier et al. 2002; Enculescu et al. 2007).
In the present paper, we report on the synthesis of
Ni–Cu alloy nanowires and their magnetic character-
ization. The influence of the material composition on
their magnetic behavior has been investigated and is
explained in detail.
E. Matei � I. Enculescu (&) � A. Leca �C. Ghica � V. Kuncser (&)
National Institute of Materials Physics, Magurele, P.O.
Box MG 7, 77125 Bucharest, Romania
e-mail: encu@infim.ro
V. Kuncser
e-mail: kuncser@infim.ro
M. E. Toimil-Molares
Gesellschaft fuer Schwerionenforschung, Planckstrasse 1,
64291 Darmstadt, Germany
123
J Nanopart Res (2013) 15:1863
DOI 10.1007/s11051-013-1863-3
Experimental
Polycarbonate foils were irradiated with highly ener-
getic (*2 GeV) heavy ions applying a fluence of
109 ions/cm2. The tracks created by the ions in the
polymer were selectively etched to 70 nm diameter
pores, in an aqueous 5 M NaOH solution with
10 vol% methanol at 50 �C.
On one side of the template we sputtered a 50 nm
thick gold film and electrochemically reinforced it
with a 10 lm thick copper layer. This conductive layer
acts as a working electrode. The electrolyte was a
modified Watts bath containing NiSO4 (225 g/l),
NiCl2 (30 g/l), CuSO4 (2 g/l), H3BO3 (32.5 g/l), and
polyvinylpyrrolidone (PVP) (5 g/l). The copper con-
centration in the bath was *100 times lower than
nickel’s (very unbalanced concentrations), due to the
fact that it deposits at less electronegative potentials.
Polyvinylpyrrolidone improves pore wetting. The
electrodeposition was performed at 50 �C in a three-
electrode configuration and was controlled by a
PARSTAT 2276 potentiostat. A saturated calomel
electrode (SCE) and a 1 cm2 platinum plate were
employed as reference and auxiliary electrodes,
respectively.
Morphology, composition, and structural aspects
were analyzed by scanning electron microscopy
(SEM), energy dispersive X-ray spectroscopy (EDX),
and X-ray diffractometry (XRD) with Cu Ka radiation,
after dissolving the templates. On the same nanowires,
transmission electron microscopy (TEM) investiga-
tions have been performed using a JEM ARM 200F
electron microscope operated at 200 kV. The micro-
scope, provided with a Quantum SE Gatan image filter,
has been used for elemental mapping by energy-
filtered transmission electron microscopy (EFTEM).
Magnetic measurements have been performed by
SQUID magnetometry (MPMS XL from Quantum
Design) under the high-sensitivity reciprocal space
option, with nanowires grown in the template. The
magnetic field was applied both perpendicular and
parallel to the wires onto 0.08 cm2 rectangular sample
pieces.
Results and discussions
Figure 1a displays the electrochemical polarization
curves measured at a scan rate of 5 mV/s. At voltages
less negative than -750 mV, the current is relatively
low and corresponds to copper deposition. At more
electronegative potentials, the current steadily
increases and both nickel and copper are reduced.
Two peaks were observed during the first sweep,
attributed to catalytic effect of the substrate.
The chronoamperometric curves for a set of
samples electrodeposited at different overvoltages
are plotted in Fig. 1b. All curves display three
characteristic regions: (i) polarization, (ii) steady
current during deposition inside the pores, and (iii)
current increase when the pores are completely filled
and caps grow on membrane’s top surface (Kronmul-
ler et al. 1988). By integrating the current in region (ii),
we determined the charge employed during the
nanowire growth for all overvoltages. We obtain
similar values (\10 % differences), indicating that
almost equal amounts of mass were deposited, as
expected since templates of identical characteristics
were employed.
The composition of the nanowires was investigated
by EDX. Nanowires consisting of alloys with the
following average formula correspond to the analyzed
samples: Ni0.2Cu0.8 (S1 deposited at -800 mV),
Ni0.54Cu0.46 (S2 deposited at -900 mV), Ni0.75Cu0.25
(S3 deposited at -1,000 mV), and Ni0.92Cu0.08 (S4
deposited at -1,050 mV). These results demonstrate
that the nickel-to-copper ratio increases as the over-
potential becomes more electronegative (Fig. 1c).
Figure 1d shows a SEM image of Ni–Cu nanowires
dissolved from the template, displaying cylindrical
shape along their entire length and smooth walls. The
wire diameter is approximately 80 nm and the length,
corresponding to the membranes thickness, 30 lm.
Figure 1e presents the XRD patterns evidencing just a
Ni-like face-centered cubic (fcc) structure textured
along the [111] direction, for samples S2–S4 and two
fcc phases due to distinct Ni and Cu precipitates in
sample S1.
The low-magnification TEM image in Fig. 2a
reveals general morphological aspects concerning
the sample S1. The corresponding nanowires are
polycrystalline while the inserted selected area elec-
tron diffraction (SAED) pattern corresponding to the
TEM image does not indicate a preferential growth
along any well-defined crystallographic direction. We
have used EFTEM imaging in order to map out the
spatial distribution of the two elements in the sample
(Cu and Ni), and thus to reveal any possible phase
Page 2 of 9 J Nanopart Res (2013) 15:1863
123
segregation. The 3-windows method has been
employed to obtain the filtered images using the Ni
L3,2 and Cu L3,2 edges at 855 and 931 eV, respec-
tively. The specimen relative thickness, t/k, varies
between 0.9 and 1.1 for single nanowires (not shown
here), where t stands for specimen thickness and k for
the electron mean free path. The Ni L3,2 and Cu L3,2
maps (Fig. 2b and c, respectively) are rather comple-
mentary, clearly showing that most of the nanowires
contain single element domains, where either Cu or Ni
is present. The Ni or Cu complementary areas are
better illustrated in false colors by the composite
image in Fig. 2d where green and red areas correspond
to Ni and Cu domains, respectively. The same EFTEM
acquisition parameters (exposure time, pixel binning,
filter slit position and width) have been used for
mapping Cu and Ni in the case of sample S3 (Fig. 3).
One can notice the much weaker Cu signal compared
to sample S1. Areas showing a somewhat higher
copper content are most likely an artifact, as they
actually correspond to overlapping nanowires (relative
thickness t/k[ 2.4), modifying therefore the signal-
to-background ratio for the Ni and Cu edges. In our
opinion, the EFTEM data from Fig. 3 confirm that the
as-grown nanowires in sample S3 contain Ni and Cu
homogeneously distributed (no chemical segregation),
with a rather low Cu content, in agreement with SEM–
EDX and XRD results.
Figure 4 displays the magnetic hysteresis loops
measured at two different temperatures (10 and
300 K), in fields up to 10 kOe. The magnetic field
was applied parallel (filled symbols) and perpendic-
ular (empty symbols) to the wires, respectively. The
raw data of the first quadrant are plotted in the insets.
One can observe an enhanced diamagnetic contribu-
tion in case of measurements performed with the field
applied perpendicular to the foil, as compared to the
case of the field applied along the foil.
To analyze the wires’ ferromagnetic behavior, the
diamagnetic contribution of the template has to be
subtracted. The question is of either considering a
Fig. 1 a Electrochemical polarization curves for NiCu alloy
deposition. The sweep rate is for all curves 5 mV/s. b Chrono-
amperometric curves recorded during potentiostatic deposition
of NiCu nanowires at different potentials. c Copper and nickel
content versus deposition potential. d Representative SEM
image of 70 nm diameter Ni–Cu nanowires, dissolved from the
template. e XRD diffraction patterns (k = 0.154 nm) of the Ni–
Cu samples
c
J Nanopart Res (2013) 15:1863 Page 3 of 9
123
same diamagnetic contribution in both geometries
(estimated from the negative slope observed at higher
fields applied perpendicular to the foil plane) or a
geometry dependent contribution. An extrinsic reason
for such anisotropy was mentioned as the filling factor
used in the fitting routine of the SQUID magnetometer
by Ney in 2011 (the correction factor counting the
deviation from the point-dipole approximation is
different in the two geometries). An additional mea-
surement performed on a polycarbonate foil evidenced
a diamagnetic constant of about -2 9 10-8 emu/Oe,
for the field perpendicular to the foil and a diamagnetic
constant one order of magnitude lower, for the field
applied along the foil. Therefore, the diamagnetic
contribution of the template has been subtracted
differently in the two geometries, under the assump-
tion of neglecting relative contribution in case of field
perpendicular to the wires (parallel to the foil). The
loops (Fig. 4), plotted from -3,000 to 3,000 Oe, show
strong dependence on the measurement geometry. For
all samples excepting the one with the lowest Ni
content (S1), a clear saturation, approaching almost
the same value in both the measurement geometries,
can be observed. As expected, the saturation values
increase with Ni content. Taking into account the
geometry of the samples (e.g., membrane sur-
face = 0.08 cm2, pore diameter = 80 nm, pore
length = 30 mm, and pore density = 109 cm-2), we
estimated the volume of magnetic alloy at
115 9 10-6 cm3 on each cm2 area. Since Ni and Cu
present similar densities (about 8.9 g/cm3), the same
value can be considered for the alloy density,
independently on the content. Hence, the average
magnetic moment per formula unit can be evaluated. It
is plotted in Fig. 5a, together with a typical depen-
dence versus Ni content (dashed line), as experimen-
tally, empirically, and theoretically reported for
Ni–Cu alloys (as for example, by Richter and Eschrig
1988). The measured values deviate from the expected
dependence more consistent than relative errors of
\10 %, due to the experimental uncertainties. Accord-
ingly, for high Ni content alloy, i.e., high overvoltage
Fig. 2 a TEM image of the CuNi nanowires in sample S1 and
corresponding SAED pattern inserted; b EFTEM image
showing the Ni L3,2 elemental map; c EFTEM image showing
the Cu L3,2 elemental map; d composite image in false colors
showing the Cu and Ni distribution in the nanowires (red copper,
green nickel). (Color figure online)
Page 4 of 9 J Nanopart Res (2013) 15:1863
123
deposition, one can assume a lower density of filled
pores probably due to hydrogen bubbles evolution at
electrode, leading regularly to lower average magnetic
moments (nanometer sized pores might be assumed
while the TEM image clearly proves unbroken wires).
For the lowest Ni content, no magnetic moment should
be measured, contrary to our result for sample S1
which present a small but finite magnetic moment.
Nevertheless, this peculiar magnetic behavior of
sample S1 is a consequence of nanowire inhomoge-
neity in agreement with the precipitation of distinct Ni
and Cu phases, as evidenced by XRD and EFTEM.
A loop of rectangular shape would be expected in
the frame of the Stoner–Wohlfarth model, when the
magnetic field is parallel to the wires and a quasilinear
shape of negligible coercive field in the case of
perpendicular field orientation. This theory assumes
coherent rotation of the spins with respect to a uniaxial
direction of anisotropy (Kuncser et al. 2010). Our
experiments reveal intermediate situations depending
on the Cu content, which can be attributed to various
reasons, as also mentioned by Sellmeyer et al. (2001)
and Ross et al. (2002). The rounded loops, for
magnetic fields applied along the wires, involving
different coercive and saturation fields for a same
system, could be due to: (i) domain formation in the
wire, (ii) distributed switching fields related to either
distributed dipolar interactions or distributed anisot-
ropy constants, or (iii) angular distributed easy axis. In
case of nanowires, the shape anisotropy, Ks (propor-
tional to Ms2) plays an important role, being compa-
rable or higher than the crystalline anisotropy Ku. The
Fig. 3 a Low-magnification TEM image of the CuNi nano-
wires in sample S3; b EFTEM image showing the Ni elemental
map; c EFTEM image showing the Cu elemental map;
d composite image in false colors showing the Cu and Ni
distribution in the nanowires (red copper, green nickel). (Color
figure online)
J Nanopart Res (2013) 15:1863 Page 5 of 9
123
domain structure in such a cylinder depends on both
the ratio Q = Ku/Ks as well as the ratio between its
diameter and the wall thickness (Sellmeyer et al. 2001;
Ross et al. 2002) defined via the exchange length
parameter kex ¼ pffiffiffiffiffiffiffiffiffi
A=Kp
, with A the exchange stiff-
ness coefficient and K the anisotropy constant. Satu-
ration magnetization values decreasing with Cu
content x, from about 300 emu/cm3 (for x = 0.08) to
45 emu/cm3 (for x = 0.8) have been estimated for the
involved systems (the values at RT are not signifi-
cantly different from the ones at 10 K). Correspond-
ingly, the evaluated shape anisotropy constants
decrease from about 30 9 104 erg/cm3 (for x =
0.08) to 2 9 104 erg/cm3 (for x = 0.46) and 0.6 9
104 erg/cm3 (for x = 0.8). Sample S1 (with x = 0.8),
where the presence of magnetic order can be explained
by an inhomogeneous distribution of magnetic atoms
(e.g., Ni clustering) will be out of further estimations.
Ku has been roughly evaluated for samples with
x \ 0.6, by correcting the Ni value (about
-5 9 104 erg/cm3, according to Mansuripur 1995)
via a factor (1 - x/0.61), similar as for the average
magnetic moment of the CuxNi1-x alloy (Ku = 0 was
assumed at x = 0.61, where the alloy loses its
magnetic moment). Just sub-unitary Q factors
Fig. 4 Magnetic hysteresis loops at 10 and 300 K, measured
with magnetic field applied parallel (filled symbols) and
perpendicular (empty symbols) to the wires, for S1 (a), S2 (b),
S3 (c), and S4 (d) samples. Inset raw data from first quadrant
Fig. 5 The average magnetic moment (a) and apertures of the
angular distribution of easy axis (b) versus the Cu content. Inset
values of the orientation ratios
Page 6 of 9 J Nanopart Res (2013) 15:1863
123
increasing with the Cu content from 0.15 (for
x = 0.08) to 0.5 (from x = 0.46) have to be men-
tioned. Thus, the shape anisotropy plays the dominant
role in the switching process for all the examined
samples with x \ 0.6, in spite of the fact that at higher
Cu content, the crystalline anisotropy becomes more
competitive. The stiffness constant A is given by A ¼ðJzS2Þ=ð12dÞ (Mansuripur 1995), with J the exchange
integral, z, the number of magnetic neighbors, S the
spin of the magnetic atom, and d the average distance
between the magnetic atoms. While these parame-
ters are dependent on the composition of the Ni–Cu
alloys, an alternative expression provided by typical
connection between the exchange integral and the
Curie temperature, TC, is preferred: A ¼ ð3kBTCSÞ=ð12dðSþ 1ÞÞ. Within the assumptions that the average
spin values of the alloys are much lower than 1 (e.g.,
even for Ni the spin value is about 0.3) and the average
spin and Curie temperature can be expressed as values
for Ni multiplied by the correction factor of (1 - x/
0.61), it results: A ¼ ANið1� x=0:61Þ2. Values of
about 8 9 10-7 erg/cm have been reported for the
stiffness constant of Ni (Michels et al. 2000). Hence,
values of about 50 nm have been estimated for the
exchange length parameter kex, a ratio D/kex of about
1.2 (slightly decreasing with x) being obtained for the
80 nm diameter wires. According to micromagnetic
simulations (Ross et al. 2002), a flower-like spin
structure (lack of magnetic domains, but surface spins
slightly misaligned) corresponds to wires with D/
kex \ 4, high aspect ratio and low Q. It is worth
mentioning that an average structural coherence
length of about 350 nm was estimated from the line-
width of XRD patterns of the single phase S2–S4
samples, which can be interpreted as the length of the
crystallites, L0, along the cylinder axis. Hence, the
analyzed wires can be also seen as a chain of
crystallites, each one of high aspect ratio. According
to Sellmeyer et al. (2001), for kex/L0 \ 1 and D/kex
close to 1, a non-cooperative and one-dimensional
magnetic regime might be considered for each wire.
Thus, in a decreasing magnetic field applied along the
cylinder axis, after reaching the saturation, the mag-
netization is independently reversed in each crystallite
with a switching field which might be approached via
the phenomenological expression for coercivity,
Hc = aH0 ? bMs (Kronmuller et al. 1988), with H0
the Stoner–Wohlfarth switching field (2Ku/Ms), a
depending on the orientation of grain texture versus
the applied field and b equating in absolute value the
demagnetizing factor (0.5 and 2p can be roughly
considered for a and b in the present case). Accord-
ingly, for crystallites of low Q values (Q � 1), the
magnetocrystalline anisotropy term becomes negligi-
ble and the switching field have to be related just to the
shape anisotropy (Hsw = 2pMs). In spite of the non-
cooperative magnetic regime, the switching field in
such crystallites of high aspect ratio and low Q values
is almost the same, and during the magnetization
reversal (after the saturation), each wire can be
considered as a magnetic monodomain switching its
magnetization at a given field. Certainly, such a field
cannot be related to switching against dipolar interac-
tions. A general expression for the magnetostatic
energy of two entities with arbitrary shapes was given
by Beleggia et al. (2004). A simplified expression for
the interaction energy of cylindrical magnetic entities
with high aspect ratio and the geometrical parameter
q ¼ D=R (R = the average distance between the
entities, about 330 nm in the present case) lower than
0.25 (as is the case) is Eint ¼ ðUiUj=RÞ (Beleggia et al.
2004), with Ui ¼ aipMiD2=4 (ai ¼ �1 and Mi the
magnetization of entity i). An average switching field,
Hsw, was estimated, values lower than 1 Oe being
obtained and proving that the dipolar interaction is
negligible. Contrary, switching fields of hundreds Oe
are required for exceeding the shape anisotropy energy
(using the same procedure and the above mentioned
shape anisotropy constants). While the observed
coercive fields for applied fields parallel to the wires
are of the same order (about 160(20) Oe at RT and
400(20) Oe at 10 K), for all samples, the involved
switching fields have to be related mainly to the shape
anisotropy energy. A distribution of such switching
fields could have two origins: (i) a distribution of
anisotropy energies or (ii) an angular distribution of
the anisotropy axes. In the first case, the coercive field,
seen as an average switching field, should depend
significantly on the alloy composition, while
HswðxÞ / MSðxÞ. The magnetization at saturation
decreases from about 300 emu/cm3 in sample with
x = 0.08–80 emu/cm3 in sample with x = 0.46,
whereas the coercive field varies by \12 % at RT
and 5 % at 10 K, excluding origin (i) as a main
contribution. Hence, the specific geometry-dependent
hysteresis loops seem to be explained via an easy axis
J Nanopart Res (2013) 15:1863 Page 7 of 9
123
distribution (EAD), involving angular distributed
anisotropy axes (Kuncser et al. 2003). The angular
dispersion of the nanowires inside the polymer is
physically better than few degrees (it is worth noticing
that contrary to structural and morphologic measure-
ments, the magnetic measurements were performed
with the nanowires fixed in the polymer template; and
due to the prevalence of the shape anisotropy, the
magnetization should align along the nanowire length,
respecting therefore the very narrow angular distribution
of the ion-tracks). Thus, the observed angular distribu-
tion of the spin directions may be related to a flower-like
spin structure, depending on composition. The param-
eters of the angular distribution can be estimated by
using the orientation ratio, OR, defined as the ratio
between the remanent magnetization in parallel and
perpendicular geometry, respectively, (Kuncser et al.
2003). In the simplest case of an uniform angular spin
distribution (Kuncser and Keune 2011; the probability
distribution is a finite constant for spin orientations up to
an angular deviation a0 and zero outside this angular
interval), it can be proven that a0 = 2arctg(OR). The
obtained a0 values are shown in Fig. 5b, whereas the
starting experimental values of OR are shown in the
inset. It can be observed that except the sample with the
highest Cu content (x = 0.8), the apertures are between
10� and 25� (just the static regime at the lowest
temperature is considered) and increase with the Cu
content. That is not surprisingly, given the increase of
the Q factor with the Cu content, leading therefore to a
challenging contribution of the magnetocrystalline
energy. The sample of highest Cu content presents an
angular aperture of about 90�, standing for a randomly
distributed spin orientation, typical to disordered ferro-
magnets. However, its magnetism cannot be discussed
according to the above considerations due to the peculiar
heterogeneous phase structure.
Conclusions
Nanowires of Ni–Cu alloys of narrow size distribution
and high aspect ratio (80 nm diameter and 30 lm
length) were grown by electrodeposition in etched
ion-track membranes. The alloy composition was
varied from 8 to 80 % of Cu, by the deposition
potential. The compositional dependent magnetic
configuration was analyzed starting from the geom-
etry-dependent magnetization reversal and suitable
estimations with respect to the average magnetic
moment, anisotropy constants and energies, exchange
length parameters, interactions between nanowires,
switching fields, and angular apertures of EADs. The
estimated average magnetic moment of the alloys
does not follow the typical linear decrease versus the
Cu content, due to lower average densities of the wires
(gas evolution at higher deposition potential) and the
heterogeneous composition (at the highest Cu con-
tent). Estimations of reference material parameters
give support for nanowires consisting of a chain of
polycrystals of high aspect ratio and non-cooperative
magnetic response. Due to the predominance of the
shape anisotropy over the magnetocrystalline anisot-
ropy in any crystallite, the magnetic reversal in each
wire takes place at an almost unique switching field,
similar as for a magnetic monodomain wire. A flower-
like spin structures and the presence of an EAD which
depends on the alloy content were observed. The
angular aperture of the distribution increases at higher
Cu content, due to a more competitive contribution of
the magnetocrystalline anisotropy.
Acknowledgments The financial support through the
exploratory research project PCE IDEI 75/2011 is highly
acknowledged.
References
Beleggia M, Tandon S, Zhu Y, De Graef M (2004) On the
magnetostatic interactions between nanoparticles of arbi-
trary shape. J Magn Magn Mater 278:270–284
Enculescu I, Toimil-Molares ME, Zet C (2007) Current per-
pendicular to plane single-nanowire GMR sensor. Appl
Phys A 86:43–47
Fert A, Piraux L (1999) Magnetic nanowires. J Magn Magn
Mater 200:338–358
Gravier L, Wegrowe J-E, Wade T et al (2002) Thermopower and
GMR of a single Co–Cu multilayer nanowire. IEEE Trans
Magn 38:2700–2702
Kronmuller H, Durst KD, Sagawa M (1988) Analysis of the
magnetic hardening mechanism in RE-FeB permanent
magnets. J Magn Magn Mater 74:291–302
Kuncser V, Keune W (2011) Step-shape angular spin distribu-
tion in layered systems by 57Fe Mossbauer spectroscopy: a
general treatment. J Magn Magn Mater 323:2196–2201
Kuncser V, Keune W, Vopsaroiu M et al (2003) Easy axis dis-
tribution in modern nanoparticle storage media: a new
methodological approach. J Optoelectron Adv Mat
5:217–226
Kuncser V, Schinteie G, Palade P et al (2010) Magnetic prop-
erties of Fe–Co layers and Fe–Mn/Fe–Co bilayers obtained
by thermo-ionic vacuum arc. J Alloys Compd 499:23–29
Page 8 of 9 J Nanopart Res (2013) 15:1863
123
Mansuripur M (1995) The physical principles of magneto-
optical recording. Cambridge University Press, Cambridge
Martin CR (1994) Nanomaterials—a membrane-based synthetic
approach. Science 266:1961–1966
Matei E, Ion L, Antohe S, Neumann R, Enculescu I (2010)
Multisegment CdTe nanowire homojunction photodiode.
Nanotechnology 21:105202
Michels A, Weissmuller J, Widenmann A, Barker JG (2000)
Exchange-stiffness constant in cold-worked and nano-
crystalline Ni measured by elastic small-angle neutron
scattering. J Appl Phys 87:5953–5955
Ney A (2011) Magnetic properties of semiconductors and sub-
strates beyond diamagnetism studied by superconducting
quantum interference device magnetometry. Semicond Sci
Technol 26:064010
Ohgai T, Gravier L, Hoffer X et al (2003) Template synthesis
and magnetoresistance property of Ni and Co single
nanowires electrodeposited into nanopores with a wide
range of aspect ratios. J Phys D 36:3109–3114
Ozin GA (1992) Nanochemistry: synthesis in diminishing
dimensions. Adv Mat 4:612–649
Richter A, Eschrig H (1988) LCAO-CPA for disordered ferro-
magnetic 3d transition metal alloys. Magnetic moment
formation in NiCu and FeCo. Phys Scr 37:948–951
Ross CA, Hwang M, Shima M et al (2002) Micromagnetic
behavior of electrodeposited cylinder arrays. Phys Rev B
65:144417
Sellmeyer DJ, Zheng M, Skomski R (2001) Magnetism of Fe,
Co and Ni nanowires in self-assembled arrays. J Phys
Condens Matter 13:R433–R460
Sugawara A, Streblechenko D, McCartney M, Scheinfein MR
(1998) Magnetic coupling in self-organized narrow-spaced
Fe nanowire arrays. IEEE Trans Magn 34:1081–1083
Toimil Molares ME, Buschmann V, Dobrev D, Neumann R,
Scholz R, Schuchert IU, Vetter J (2001) Single-crystalline
copper nanowires produced by electrochemical deposition
in polymeric ion track membranes. Adv Mat 13:62–65
Yi G, Schwarzacher W (1999) Single crystal superconductor
nanowires by electrodeposition. Appl Phys Lett 74:
1746–1748
J Nanopart Res (2013) 15:1863 Page 9 of 9
123