Magnetic properties of Fe2O3 -TeO2 - Bi2O3 glasses
P. Sandhya Rani and R.Singh*
School of Physics, University of Hyderabad, Central University P.O., Hyderabad 500046, India
*corresponding author email : rsinghsp@gmail.com, Tel.: +9140 2313 4321; Fax: +9140 23010227
Abstract
The glasses of composition 20Fe2O3 - (80-x)TeO2-xBi2O3
(x= 0-20mol %) were prepared by melt quenching method.
Electron spin resonance (ESR) and magnetization
measurements indicate the existence of short range
antiferromagnetic (AFM) interactions between Fe ions
which increases with increase in Bi2O3 content in these
glasses.
Keywords: Oxide glasses, Electron Spin Resonance ,
magnetic interactions, susceptibility.
Introduction
The study of the magnetic properties of oxide glasses
with transition metal (TM) ions gives useful information
on the valence states and magnetic interactions between
TM ions in a vitreous matrix, as well as on the
distribution mode of magnetic ions in the glass network.
Electron spin resonance (ESR) spectra show distinct
resonance lines for the paramagnetic ions involved in
structural units of well-defined symmetry and those
connected in clusters [1].
Experimental
The glasses of composition 20Fe2O3 - (80-x)TeO2xBi2O3 (x = 0, 5, 10, 15, 20 mol %) were synthesized by
melt quenching method. Amorphous nature of the ascast samples was confirmed from XRD studies. The
ESR spectra of the samples were recorded on Joel XBand ESR spectrometer. The magnetization (M)
measurements were done using model 7400 Lake Shore
Cryotronics Magnetometer.
Fig.1.ESR spectra for the glass samples at room
temperature (293K).
fig.2. Two straight lines fit as per Curie-Weiss law with
change of slope at ~ 200K are obtained. The Curie
temperature (θc) is negative for both the linear fit
regions. The lower value of θc are obtained for Bi2O3
doped glasses in 80 < T < 200 temperature range. The
data indicates that magnetic interactions between the
iron ions in the present glasses are predominantly antiferromagnetic. The interaction increases with the
addition of Bi2O3 in the glass matrix. However, as the
temperature decreases below 200 K the interaction
weakens in the Bi2O3 doped glasses.
Results and discussion
Fig 1 shows ESR spectra of the present glass
system at room temperature. All the compositions show
broad resonance centered at g ~ 2.0 with resonance line
width ΔHpp = 325 ± 25 mT. The intensity J (≈ I∆HPP2)
of ESR signal decrease with increase in Bi2O3 content.
With the addition of Bi2O3, the Fe3+ ions convert into
Fe2+ ions leading to increased antiferromagnetic
interaction and decrease in J value. In these glasses the
isolated Fe ions are not detected. All Fe ions are
coupled antiferromagnetically in the form of clusters
(dimers or triads). The addition of Bi2O3 does not
change the cluster formation and create isolated Fe ions.
The M and susceptibility (χ) decrease with increase in
Bi2O3 content The inverse of susceptibility (-1)
versus T plots for various glass samples are shown in
Fig.2. H/M vs. T plots for the glass samples.
References
[1] P. Sandhya Rani and R. Singh, Electron spin
resonance and magnetization studies of ZnO-TeO2Fe2O3 glasses, J. Phys. Chem. Solids, 74 (2013) 338343.