Magnetic and dielectric study of α-Fe1.6Ga0.4O3
Abdul Gaffar Lone*, R. N. Bhowmik
Department of Physics, Pondicherry University, R. V. Nagar, Kalapet, Pondicherry-605014, India
*
Corresponding author’s e-mail: agl221986@gmail.com, Tel.: +91-8015398640
Abstract
α-Fe1.6Ga0.4O3 with grain size  45 nm has been prepared. The
sample showed ferromagnetic properties and magnetic
moment has been enhanced by non-magnetic Ga doping in αFe2O3. Dielectric measurement exhibited a signature of metalsemiconductor/insulator transition near to Morin transition,
which is related to spins flipping process in rhombohedral
lattice structure.
Keywords: Ga doped hematite, Ferromagnetism,
semiconductor, metal-insulator transition.
increases from the value 72 at 243K to 255 at 263 K and 1166
at 303 K. This is attributed to hopping mechanism of charge
carriers [6]. The temperature dependence of relaxation time
(τ(T)), which obtained from the impedance analysis at
different measurement temperatures. The τ(T) plot (Fig. 1(c)),
following Arrhenius law, indicated semiconductor to metallic
transition at  380 K and metal to semiconductor/ insulator
transition  300 K. The activation energy was found  0.64 eV
and 0.17 eV for high and low temperature regimes,
respectively. These transitions in dielectric relaxation are also
revealed in the temperature dependence of conductivity plot.
Introduction
Sample preparation
Stoichiometric weight ratio of α-Fe2O3 and β-Ga2O3
were mechanically alloyed up to 25 hrs in air using FRITISCH
(Pulverisette 6, Germany) planetary mono miller. The alloyed
powder was pressed into pallets, which were annealed at 800
oC for 2 hrs. under high vacuum condition.
Results and discussion
X-ray diffraction pattern and profile fitting in Fig.
1(a) are consistent to single phased α-Fe2O3 (rhombohedral)
structure. The lattice constants of α-Fe1.6Ga0.4O3 were found to
be a = 5.0383 Å and c =13.754 Å. Fig. 1(b) shows magnetic
hysteresis loop at room temperature. The hysteresis loop is not
saturated even at 16 kOe magnetic field. We noted increase of
magnetization in α-Fe1.6Ga0.4O3 in comparison to α-Fe2O3.
The coercivity decreased in Ga doped sample (~1615 Oe for
α-Fe2O3 and ~1020 Oe for α-Fe1.6Ga0.4O3). The smaller
coercivity and higher magnetization could be useful in various
spintronics applications of metal doped hematite material. The
signature of TM in Ga doped hematite is noted at 270 K [5].
We measured dielectric properties of the sample in
the frequency range 1-106 Hz and temperature range 123–563
K. The temperature dependence of dielectric constant (ε′)
showed an abrupt increase above TM. For example, ε′ at 1Hz
(a)
experiment
profile fit
expt.- fit
Bragg position
Intensity (arb. units)
20
0.6
30
40
50
2 (Degrees)
60
70
80
(c)
(b)
0.01
0.4
Eg=0.17 eV
0.2
1E-4
0.0
(s)
M (emu/g)
There is a great deal of interest in iron oxides, mostly in nanosized particles, for both fundamental study and technological
applications. Hematite (α-Fe2O3) is the most stable polymorph
of iron oxide (Fe2O3). The crystal structure of α-Fe2O3
(hematite) is corundum type, where Fe3+ions occupy twothirds of the available octahedral sites and the adjacent planes
of Fe3+ ions are separated by layers of oxygen (O2-) ions. The
two magnetic sub-lattices (planes) are oriented along the
rhombohedral [111] axis and antiparallel to each other. αFe2O3 is an antiferromagnet with Neel temperature (TN)  960
K. Below TN, a weak ferromagnetism is observed due to spin
canting with respect to rhombohedral planes and becomes
typical antiferromagnet due to out of plane spin ordering
below Morin transition (TM)  263 -270 K [1]. The magnetic
and electrical properties of hematite are influenced by particle
size, and metal doping [2, 3]. There is a possibility of low drift
mobility of charge carriers between TM and TN, which are
affected by magnetic spin ordering [4]. In this work, we report
the properties of α-Fe1.6Ga0.4O3 (Ga doped α-Fe2O3).
-0.2
1E-6
-0.4
metallic
semiconductor
Eg = 0.64 eV
-0.6
-15 -10
-5
0
5
H (KOe)
10
15
1E-8
1.5 2.0 2.5 3.0 3.5 4.0 4.5

( )
Fig. 1 XRD pattern and profile fit (a), ferromagnetic loop (b),
and temperature dependence of relaxation time (c).
Conclusions
The non-magnetic Ga doping in hematite (α-Fe2O3) structure
has shown enhancement of soft ferromagnetism. The hopping
mechanism of electrical charge carriers seems to be affected
by the magnetic spin ordering above and below of the Morin
transition temperature  270 K. The system is an nonconventional magnetic semiconductor, whose properties can
be tuned by varying Ga content in hematite structure.
Acknowledgment
The authors thank CIF, Pondicherry University for providing
magnetic and dielectric measurements facilities. The authors
also acknowledge the research grants from DST (NO. SR/S2/
CMP-0025/2011) and CSIR (No. 03(1222)/12/ EMR_II),
Govt. of India.
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