We have investigated the structural and magnetic properties of Co1-xVx nanoparticles (NPs) with composition x = 0.25 (stoichiometric) and 0.29 (under-stoichiometric) prepared by the cluster-beam deposition (CBD) technique. Our data shows that the as-made Co1-xVx NPs are a mixture of the high-temperature phase (HTP) and the low-temperature phase (LTP) of Co3V and the particles are superparamagnetic at room temperature (RT) with blocking temperatures (TB) of 90 and 137 K for x = 0.25 and 0.29, respectively. This behavior contrasts with the bulk which are paramagnetic down to 4.2 K. When the Co75V25 NPs are annealed at 573 K, they undergo a phase separation into a mixture of phases and become ferromagnetic at room temperature with Curie temperature (Tc) of 515 K

Abel, F. M.

Balamurugan, B.

Hadjipanayis, G. C.

Ruzybayev, I.

Sellmyer, D. J.

Skomski, R.

Tosun, Onur

English

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Faculty Publications, Department of Physics 
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2019 
Structural and magnetic properties of Co-V nanoparticles 
Onur Tosun 
I. Ruzybayev 
F. M. Abel 
B. Balamurugan 
R. Skomski 
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Authors 
Onur Tosun, I. Ruzybayev, F. M. Abel, B. Balamurugan, R. Skomski, D. J. Sellmyer, and G. C. Hadjipanayis 
AIP Advances 9, 125144 (2019); https://doi.org/10.1063/1.5130456 9, 125144
© 2019 Author(s).
Structural and magnetic properties of Co-V
nanoparticles
Cite as: AIP Advances 9, 125144 (2019); https://doi.org/10.1063/1.5130456
Submitted: 03 October 2019 . Accepted: 12 November 2019 . Published Online: 27 December 2019
O. Tosun , I. Ruzybayev, F. M. Abel , B. Balamurugan, R. Skomski, D. J. Sellmyer, and G. C.
Hadjipanayis
COLLECTIONS
Paper published as part of the special topic on 64th Annual Conference on Magnetism and Magnetic Materials
Note: This paper was presented at the 64th Annual Conference on Magnetism and Magnetic Materials.
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AIP Advances ARTICLE scitation.org/journal/adv
Structural and magnetic properties
of Co-V nanoparticles
Cite as: AIP Advances 9, 125144 (2019); doi: 10.1063/1.5130456
Presented: 8 November 2019 • Submitted: 3 October 2019 •
Accepted: 12 November 2019 • Published Online: 27 December 2019
O. Tosun,1,a) I. Ruzybayev,1,2 F. M. Abel,1 B. Balamurugan,3,4 R. Skomski,3,4 D. J. Sellmyer,3,4
and G. C. Hadjipanayis1
AFFILIATIONS
1Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19711, USA
2Kinsley School of Engineering, York College of Pennsylvania, York, Pennsylvania 17403, USA
3Department of Physics and Astronomy, University of Nebraska, Lincoln, Nebraska 68588, USA
4Nebraska Center for Materials and Nanoscience, University of Nebraska, Lincoln, Nebraska 68588, USA
Note: This paper was presented at the 64th Annual Conference on Magnetism and Magnetic Materials.
a)Corresponding author: Onur Tosun onurt@udel.edu
ABSTRACT
We have investigated the structural and magnetic properties of Co1-xVx nanoparticles (NPs) with composition x = 0.25 (stoichiometric) and
0.29 (under-stoichiometric) prepared by the cluster-beam deposition (CBD) technique. Our data shows that the as-made Co1-xVx NPs are
a mixture of the high-temperature phase (HTP) and the low-temperature phase (LTP) of Co3V and the particles are superparamagnetic at
room temperature (RT) with blocking temperatures (TB) of 90 and 137 K for x = 0.25 and 0.29, respectively. This behavior contrasts with the
bulk which are paramagnetic down to 4.2 K. When the Co75V25 NPs are annealed at 573 K, they undergo a phase separation into a mixture of
phases and become ferromagnetic at room temperature with Curie temperature (Tc) of 515 K.
© 2019 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license
(http://creativecommons.org/licenses/by/4.0/). https://doi.org/10.1063/1.5130456., s
INTRODUCTION
Bulk intermetallic compounds have attracted much attention
in many different materials because of their interesting physical
properties and technological applications.1–4 Nanoparticles (NPs)
of intermetallic compounds have shown interesting physical prop-
erties due to both size and surface effects. There are numer-
ous reports where the magnetic properties of NPs are superior
when compared to those corresponding of bulk alloys. For exam-
ple, Co2Si nanoclusters have been reported to have moment-
enhancement as compared to the bulk alloy.5 Also, Tosun et al.6
reported that nanoclusters of Co2Ge are ferromagnetic at room
temperature with Curie temperature (Tc) of 815 K in con-
trast to that of bulk which is ferromagnetic only at cryogenic
temperatures.7
The stoichiometric intermetallic Co3V compound exists in
two structures, an ordered hexagonal (Al3Pu-type) low-temperature
phase (LTP) and a cubic L12 (Cu3Au)-type high-temperature phase
(HTP). Both the LTP and HTP in bulk alloys are reported to be
paramagnetic down to 4.2 K.8,9 The same authors reported weak
ferromagnetism near 4.2 K in Co-V alloys at stoichiometric and
under-stoichiometric the LTP, possibly due to disordering when
Co atoms occupy V lattice sites. The alloys at the Co-rich side
of the LTP, however, were reported to have very large magnetic
moments (larger than the Co magnetic moment of 1.72 μB) which
may be attributed to the polarization of neighboring Co atoms by
the excess magnetic Co atoms on the V lattice sites.8 The polariza-
tion was explained to occur because “Co atoms with eight or less
Co nearest neighbors are non-magnetic as well as the V atoms, in
contrast to the magnetic Co atoms with nine or more Co nearest
neighbors.”8
Because of the interesting magnetic properties of bulk Co-V
alloys, we decided to fabricate NPs Co1-xVx NPs with x = 0.25 and
0.29 and investigate the effects of particle size and disorder on their
structural and magnetic properties. To the best of our knowledge,
there is no such study on Co1-xVx NPs.
AIP Advances 9, 125144 (2019); doi: 10.1063/1.5130456 9, 125144-1
© Author(s) 2019
AIP Advances ARTICLE scitation.org/journal/adv
FIG. 1. (a) X-ray diffraction (XRD) data of
the bulk and ribbon Co3V samples with
the reference high-temperature phase
(HTP) and low-temperature phase (LTP)
lines, (b) Hysteresis loops of the bulk and
ribbon samples at 300 K.
EXPERIMENTAL METHOD
The cluster-beam deposition (CBD) technique, which was
described elsewhere,10 was used to synthesize Co1-xVx NPs. The
NPs were prepared with 1.4 Torr Ar pressure and 70 W sputter-
ing DC power from a solid sputtering target with 75 at. % Co
and 25 at. % V. They were deposited on Si wafers and C-coated
Cu grids for magnetic, structural and microstructural analyses. For
comparison purposes, melt-spun ribbons were made at a wheel
speed of 45 m/s. The crystal structure analysis was carried out with
a Rigaku X-ray diffraction (XRD) diffractometer using Cu Kα radi-
ation with a wavelength of 1.540 Å. The microstructure and elec-
tron diffraction were made with a JEOL 3010 transmission electron
microscope (TEM) operating at 300 kV. The volumes fraction of
the nanoparticulate films were obtained with a JEOL 6330F scan-
ning electron microscope (SEM) and the compositional analyses
FIG. 2. (a) XRD pattern of the nanopar-
ticles (NPs) with the reference HTP
and LTP Co3V lines, (b) Transmission
electron microscope (TEM) micrograph
showing NPs with an average size of
6.8 nm with the inset showing the
size distribution, (c) High-resolution TEM
(HRTEM) (d) Selected area diffraction
(SAD) images of the NPs.
AIP Advances 9, 125144 (2019); doi: 10.1063/1.5130456 9, 125144-2
© Author(s) 2019
AIP Advances ARTICLE scitation.org/journal/adv
were done with energy dispersive X-ray spectroscopy (EDS). Mag-
netic measurements were made with a Quantum Design Versa Lab
vibrating sample magnetometer (VSM).
RESULTS AND DISCUSSION
As-cast bulk and melt-spun ribbons of Co3V were found to
have the cubic HTP structure.8,9 When both the bulk and ribbon
samples were annealed, they were found to exhibit the ordered
hexagonal LTP.8,9 Fig. 1a shows the XRD data of the as-made and
annealed samples as well as the reference LTP and HTP XRD pat-
terns.8,11 The lattice parameter of the as-made bulk is a = 3.564 Å
and for the annealed a = 5.020 Å, c = 12.260 Å. As-made ribbons
have a = 3.562 Å and the annealed a = 5.032 Å, c = 12.300 Å. These
values are close to the values reported by Y. Aoki et al.8,11
The as-made and annealed ribbons exhibit some weak ferro-
magnetism at room temperature (Fig. 1b) which may be due to
introduction of disorder in the ribbons during melt-spinning unlike
both the HTP and LTP of bulk alloys Co1-xVx with 0.241 ≤ x ≤ 0.301
which are paramagnetic above 4.2 K as reported by Y. Aoki et al.8,9
The as-made NPs of Co1-xVx with x = 0.25 and 0.29 were found
to have an average size of 6.8 nm and 6.3 nm, respectively. In this
article, the structural analyses of the as-made Co1-xVx NPs with
x = 0.25 (Co3V) are only presented. According to our Rietveld refine-
ment analysis, the as-made NPs have 85 vol. % of the HTP and
15 vol. % of the LTP (Fig. 2a). The lattice constant of the HTP was
determined to be a = 3.545 Å which is slightly smaller than that of
bulk. Figure 2 shows the XRD, TEM, HRTEM, and SAD data for the
as-made NPs. Both the XRD and TEM results suggest that the as-
made NPs are a mixture of small and disordered/partially ordered
particles. Fig. 2c shows a HRTEM image of the as-made NPs with a
d-spacing value of 2.06 Å which could be fitted to the (111) reflection
of the HTP and (202) of the LTP.
Thermomagnetic data (Fig. 3a) show that the Co1-xVx NPs
with x = 0.25 and 0.29 are superparamagnetic at RT with blocking
temperatures (TB) value of 137 K (Fig. 3a) and 90 K (not shown
here), respectively. Saturation magnetization (Ms) values of the NPs
with x = 0.25 (Fig. 3b) and 0.29 at 300 and 50 K are found to
be (119 emu/cm3, 140 emu/cm3) and (83 emu/cm3, 95 emu/cm3),
respectively. The Ms values at both temperatures increase with Co
concentration as shown in (Fig. 3c). The effective anisotropy con-
stant values (K) of the NPs at 50 K have been determined by fitting
the magnetization data to the law-of-approach to saturation12,13 and
they have been determined to be 1.8 and 0.4 Merg/cm3 for x = 0.25
and 0.29, respectively. The coercivity (Hc) values which are 0.21 and
0.16 kOe for x = 0.25 and 0.29, respectively (inset of Fig. 3b) and
they follow the increasing trend of K. Possible surface effects and the
existence of the LTP in the as-made NPs may be the reason of the
anisotropy.
The high temperature thermomagnetic measurements (Fig. 3d)
show that the magnetization of the as-made NPs increases at 360 K.
When the temperature is increased to 573 K and the sample is cooled
to RT, the sample is now ferromagnetic. The as-made samples were
FIG. 3. (a) Zero-field-cooled (ZFC)-Field-
cooled (FC) magnetization curves at
0.5 kOe Oe for x = 0.25, (b) Hys-
teresis loops at 300 and 50 K for
x = 0.25, (c) Saturation magnetization
(Ms) at 300 and 50 K versus at. % of
Co, (d) High temperature thermomag-
netic M(T) curves at 2 kOe for x = 0.25.
AIP Advances 9, 125144 (2019); doi: 10.1063/1.5130456 9, 125144-3
© Author(s) 2019
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FIG. 4. Structural properties of the
annealed Co3V NPs: (a) XRD pattern
of the NPs with the reference LTP
Co3V, hexagonal Co-V14 and cubic V-
rich Co solid solution15 lines, (b) TEM,
(c) HRTEM 2.04 Å which could be fitted
to the (002) reflection of the hexagonal
Co, (d) SAD images of the NPs.
then annealed at 573 K in order to investigate whether the increase
in the magnetization could be due to structural and/or magnetic
transformations in the as-made NPs. After annealing, the average
size of the NPs increased to 20 nm (inset of Fig. 4b) and the NPs
became more crystalline which is clearly observed in the XRD, TEM,
HRTEM, and SAD data shown in Figure 4.
Our XRD (Fig. 4a) suggest that the annealed NPs may be a mix-
ture of the LTP Co3V, hexagonal Co, and cubic V. The presence of
a new phase is not excluded because the peak at 62.6○ with a rela-
tively high intensity-as compared to the reference patterns-has not
yet been clearly identified. All the XRD peaks are shifted to higher
angles. A possible explanation for this is the precipitation of cubic
FIG. 5. Magnetic properties of the
annealed Co3V NPs: (a) High tempera-
ture thermomagnetic curves at 2 kOe, (b)
Hysteresis loops at 300 and 50 K.
AIP Advances 9, 125144 (2019); doi: 10.1063/1.5130456 9, 125144-4
© Author(s) 2019
AIP Advances ARTICLE scitation.org/journal/adv
V nanoclusters during the phase separation. This makes some of the
nanoclusters to be Co-rich which then may be regarded as the hexag-
onal Co. Such a phase separation in Co3V alloys was reported by
Ustinovshikov.16 Since the atomic radius of Co is smaller than that
of V, the XRD peaks of both V-rich Co and the Co-rich LTP Co3V
clusters also shift to higher angles due to the phase separation.
The annealed NPs are ferromagnetic at room temperature with
a TC = 515 K (Fig. 5a). The inset of Fig. 5a shows the method of
determination of the TC: finding the intersect of the linear part of
the M2 versus T data with the temperature axis. Their Ms values at
300 and 50 K are increased from (119 emu/cm3, 140 emu/cm3) to
(526 emu/cm3, 603 emu/cm3) as shown in Fig. 5b. Their Hc values
at 50 K are increased from 215 Oe to 500 Oe which can also be seen
in the inset of Fig. 5b. The increase in the Hc values may indicate
that the annealed NPs have predominantly the LTP or Co-rich LTP.
Their effective anisotropy values, K, at 50 K follow Hc trend and the
values are increased from 1.8 Merg/cm3 to 4.5 Merg/cm3.
CONCLUSIONS
In conclusion, nanoparticles of Co1-xVx with x = 0.25 and 0.29
have been synthesized using the gas-aggregation cluster-beam depo-
sition method and their structural and magnetic properties were
investigated. The as-made nanoparticles for x = 0.25 and 0.29 were
found to be a mixture of the HTP and LTP and are thermally blocked
at 50 K unlike the bulk which are paramagnetic down to 4.2 K. It was
observed that when nanoparticles are annealed at 573 K, they are a
mixture of the LTP Co3V, hexagonal Co, and cubic V-rich Co. The
annealed nanoparticles are ferromagnetic at room temperature with
Curie temperature of 515 K. The enhanced properties of the as-made
nanoparticles may be attributed to polarization of Co atoms due to
magnetic excess Co atoms on the V lattice sites which could occur
due to the structure not being completely ordered. This indicates
that the Co atoms with increased number of Co nearest neighbor
leads to an increase in the Co-Co exchange interaction.
ACKNOWLEDGMENTS
This research is supported by Department of Energy (DOE)
with grant number DE-FG02-04ER46152 and DE-FG02-90ER45413.
The authors also thank Alexander Gabay for making the ribbons and
for his useful suggestions.
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Structural and magnetic properties of Co-V
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Structural and magnetic properties of Co-V nanoparticles

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