This study compares the structural and magnetic properties of bulk and nano-sized Fe2CoAl samples. X-ray diffraction showed both samples had a disordered cubic structure, with the nano-sized sample having a smaller lattice parameter and broader peaks due to a smaller grain size of 13nm. Magnetization measurements found the nano-sized sample had a 10% higher saturation magnetization and 34 times higher coercivity than the bulk sample. Additionally, the Curie temperature of the nano-sized sample was over 8000C compared to 7370C for the bulk. Mössbauer spectroscopy showed the local environments of iron atoms were similar between samples, despite increased disorder in the nano-sized sample. Overall, high-energy ball mill

1. Comparative study of the structural and magnetic properties of bulk and
nano-sized Fe2CoAl
Vishal Jain, Jagdish Nehra, V. D. Sudheesh, N. Lakshmi, and K. Venugopalan
Citation: AIP Conf. Proc. 1536, 935 (2013); doi: 10.1063/1.4810537
View online: http://dx.doi.org/10.1063/1.4810537
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2. Comparative study of the structural and magnetic
properties of bulk and nano-sized Fe2CoAl
Vishal Jain, Jagdish Nehra, Sudheesh V.D., N. Lakshmi and K. Venugopalan
Department of Physics, Mohanlal Sukhadia University, Udaipur, Rajasthan, 313001, India
email:- vjain045@gmail.com
Abstract. The structural and magnetic properties of as-melted and high energy ball milled sample have been studied by
X-ray diffraction, 57
Fe Mössbauer spectroscopy and DC magnetization. The observed properties are compared to that of
the bulk sample. The magnetic hyperfine fields are related to structural disorder. There is a very good enhancement of
bulk magnetic properties in the nano-sized samples, the most notable one being a dramatic increase in saturation
magnetization and Curie temperature of the sample and are explained in terms of structural disordering and size effect.
Keywords: Heusler alloy, High energy ball milling, Magnetism
PACS: 81.07.Bc, 75.50.Bb
INTRODUCTION
Soft magnetic materials with high saturation
magnetization and high Curie temperature are required
in electronics as well as for recording technologies [1].
It is also one of the key requirements in many high
frequency applications, such as the planar inductors
and transformers used in integrated circuits. The
Slater–Pauling curve indicates that the addition of
cobalt increases the magnetization of iron.
High-density recording media now has a
requirement of ultra fine particles with stable magnetic
properties. In this study, structural and magnetic
properties of 13nm sized sample of Fe2CoAl
synthesized by high energy ball milling and that of the
bulk are compared.
EXPERIMENTAL
Fe2CoAl alloy was prepared by argon arc melting
using pure constituent metals in stoichiometric
proportions. The melting process was repeated to get
higher homogeneity. The as melted sample was milled
for 2 hours in a SPEX 8000M mixer/mill using
tungsten carbide vials and balls with a ball to powder
ratio of 20:1. Structural characterization has been done
by using X-ray powder diffraction (XRD) and
transmission electron microscopy (TEM).
Magnetization measurements were determined using a
Lakeshore 7304 model vibrating-sample
magnetometer (VSM). Room temperature Mössbauer
spectra were recorded using a 25mCi Co-57(Rh)
source. The calibration was done using Fe foil.
RESULTS AND DISCUSSION
FIGURE 1. X-ray diffraction pattern of the samples.
Figure.1 X-ray diffractogram of both samples show
formation of disordered, single phased, A2 type
structure (F m-3 m). No other phases were found from
the X-ray diffraction pattern. Fe2CoAl alloy having an
inverse type Heusler structure have also been reported
[2] and so only B2 ordering is obtainable at best.
Lattice parameter (a0) of as-melted sample (5.732Å) is
slightly smaller than reported value Fe2CoAl due to
atomic disordering between X, Y and Z. Inset of figure
VKRZV LQFUHDVH LQ ș YDOXH DIWHU KRXU PLOOLQJ
implying decrease in lattice parameter. The peaks
broaden after 2 hour high energy ball milling due to
decrease in grain size to 13nm as confirmed from
TEM micrographs.
Proceeding of International Conference on Recent Trends in Applied Physics and Material Science
AIP Conf. Proc. 1536, 935-936 (2013); doi: 10.1063/1.4810537
© 2013 AIP Publishing LLC 978-0-7354-1160-9/$30.00
935
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3. FIGURE 2. Room Temperature magnetization curves.
The value of coercivity and saturation
magnetization for as melt sample is 2Oe (Hc

4. ȝB
(Ms) per formula unit (f.u) and milled sample 68Oe
(Hc

5. ȝB (Ms) per f.u. There is an increase in
saturation magnetization of 10% in milled sample with
respect to the as-melted sample. This is due to better
ferromagnetic exchange interactions on reduction in
particle size and also anti-site disorder induced by ball
milling. The as-melted sample is magnetically
extremely soft with HC 2Oe at room temperature and
there is not much change with temperature. The value
of squarness for milled sample is enhanced.
On milling, the coercivity increases by about 34
times. This is because with the increase in milling time
and decrease in size due to milling, internal micro
strain, impurities, pores and defects also increase [3].
These defects and the surface spins act as pinning
centers which makes spin/domain wall rotations
difficult leading to an increase in HC with decrease in
size. On milling, the increase in the disordering has
also lead to the large increase in the Curie temperature,
TC of the system. The TC of the as melted sample is
7370
C while it is more than 8000
C for the milled
sample.
FIGURE 3. High temperature magnetization curves.
Three distinct sextets and a singlet are present in
the room temperature Mössbauer spectra of the as-
melted and milled samples (Figure 4). There is no
change in the hyperfine field values of individual
components and only marginal changes in the
percentage area contributions. This shows that
although the samples are disordered, on milling, no
new phase is developed and the environment to the
57
Fe atom in both samples are more or less the same.
Some preferential orientation of spins observed due to
strain as is generally observed in systems in which
micron sized flakes are created on ball milling.
FIGURE 4. Room temperature Mössbauer spectra.
In conclusion, enhancement in the important
magnetic parameters like saturation magnetization,
Curie temperature and coercivity are observed after
high energy ball milling of Fe2CoAl. Although
disordered, both samples are magnetically very soft
high saturation and high Curie temperature thus
demonstrating the synthesis of a Heusler-like, albeit
disordered, alloy which is nano sized and yet not only
retains but also improves the magnetic properties of its
bulk counterpart.
ACKNOWLEDGMENTS
The work has been supported by UGC DSA and
DST-FIST schemes of the Department of Physics, M L
Sukhadia University, Udaipur. Vishal Jain gratefully
acknowledges support from UGC DAE CSR research
project.
REFERENCES
1. D. Zhou, M. Zhou, M. Zhu, X. Yang and Ming Yue, J.
Appl. Phys. 111, 07A319-3 (2012)
2. M. Gillessen and R. Dronskowski, J. Comput. Chem. 31,
612-9 (2010).
3. R. Koohkana, S. Sharafia, H. Shokrollahib, K.
Janghorban, J. Magn. Magn. Mater. 320, 1089-1094
(2008)
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