Magnetic Properties of Flower-like FeCo binary alloy
Prakash Karipoth, and R. Justin Joseyphus
Department of Physics, National Institute of Technology, Tiruchirappalli 620 015, India
Corresponding author’s e-mail: rjustinj@nitt.edu, Tel.: +91 431 2503614; Fax: +91 431 2500133.
Abstract
FeCo alloy particles with varying composition have
been synthesized by a unique simple one-pot one-step
polyol process. The morphology of the particles are found
to be flower-like with sizes varying according to the
composition of the alloy. The magnetic, structural, and
thermal properties have been studied in detail.
Keywords: FeCo, Polyol process, shape
thermomagnetic analysis, Curie temperature.
anisotropy,
Introduction
FeCo binary alloys are remarkable for their
highest saturation magnetization of 240 emu/g (bulk).
The synthesis of composition controlled FeCo through
chemical methods is a challenge due to the highly
oxidizing nature of Fe.
Polyol process is a versatile and cost
effective method for the controlled synthesis of metals
and alloys in which the polyol itself acts as the solvent
and oxidation preventing agent [1]. The morophology of
FeCo is found to be either spherical or cubic so far [2].
Here, we present the oxide-free synthesis of flower-like
FeCo alloy particles through a unique and simple onepot one-step polyol process. The compositional and
morphological dependent structural, thermal and
magnetic properties are explored in detail.
The TEM-EDS analysis shows that the final
alloy composition is in close agreement with the
targeted composition. In contrast to the general cubic or
spherical shapes, flower-like particles are observed,
with the number of petals increasing with the cobalt
content. Fig.1. shows the FeCo particles examined using
(a) SEM and (b) TEM. The origin of flower-like shape
is suggested to be an outcome of the competing
tendency of Fe and Co atoms during growth to attain
cubic and spherical shape respectively.
The thermally induced structural transitions
and the Curie temperatures of the FeCo alloys are
determined by TMA. The bcc-fcc phase transitions and
the Curie transitions have been analyzed in comparison
with the FeCo binary alloy phase diagram and earlier
reported bulk literature values.
The magnetic properties suggest higher
coercivity compared to the bulk value due to the shape
anisotropy arising out of the flower shaped morphology.
Higher saturation magnetization values also underline
the formation of oxide free FeCo alloy particles. The
present studies indicate the potential of polyol process
in the synthesis of shape controlled Fe based alloys with
better magnetic properties.
Experimental details
The synthesis of FeCo has been carried out at
elevated temperatures around 180 oC with ethylene
glycol as solvent and Fe(II) chloride tetrahydrate, and
cobalt acetate tetrahydrate as precursors [3]. The
reaction rate is accelerated by the presence of NaOH.
The samples are characterized using X-ray diffraction
(XRD), thermomagnetic measurements (TMA),
transmission electron microscopy (TEM) and magnetic
hysteresis measurements.
Results and discussions
The XRD analysis for the as-prepared FeCo
showed a disordered bcc structure with a composition
dependent peak shift with respect to pure Fe. With
increasing Co in Fe, the lattice parameter systematically
reduces from 2.859 Å for Fe67Co33 to 2.844 Å for
Fe34Co64 which is in accordance with the bulk literature
value. No oxide or other impurity phases are observed
in the XRD profile.
Fig.1. (a) SEM micrograph of spherical shaped FeCo (b)
TEM micrograph of flower shaped FeCo.
References
[1] R. J. Joseyphus et al, J. Solid State Chem. 180,
(2007) 3008.
[2] D. Kodama et al, Adv. Mater. 18, (2006) 3154.
[3] K. Prakash et al, J. Colloid Interface Sci. 404,
(2013) 49.