J Supercond Nov Magn
DOI 10.1007/s10948-016-3761-2
ORIGINAL PAPER
EPR Studies for GdBa
2
Cu
3
O
7-δ
Added with Nanosized
Ferrite ZnFe
2
O
4
Before and After Irradiation
by 3 MeV H
+
Ions
S. Isber
1
· H. Basma
2
· S. Noureldeen
3
· M. ME. Barakat
4
· M. Roumie
5
· R. Awad
2
Received: 17 May 2016 / Accepted: 22 August 2016
© Springer Science+Business Media New York 2016
Abstract (ZnFe
2
O
4
)
x
GdBa
2
Cu
3
O
7-δ
superconducting sam-
ples, 0 ≤ x ≤ 0.40 wt%, were synthesized using a con-
ventional solid-state reaction technique. The prepared
samples were investigated using electron paramagnetic
resonance (EPR) measurements. EPR measurements were
carried out, at different temperatures 100 K ≤ T ≤ 300
K, for the prepared samples before and after irradiation by
3 MeV protons. An isotropic symmetric EPR line with g
factor ≈2 is detected for the samples before irradiation,
corresponding to Gd
3+
ions. A single strong and broad
isotropic EPR line is observed for all samples after irra-
diation with g ≈2.65. The broadness is attributed to the
superposition of signals resulting from the clustering of
Gd
3+
ions and the dipole interaction between these ions.
The number of spins (N) participating in EPR resonance
showed a decrease with increasing temperature, while the
activation energy (E
a
) experienced an increase with x up to
0.06 wt% followed by a further decrease.
H. Basma
hadibassma@gmail.com
1
Department of Physics, American University of Beirut,
PO Box 11-0236, Beirut, Lebanon
2
Physics Department, Faculty of Science, Beirut Arab
University (BAU), Beirut, Lebanon
3
Physics Department, Faculty of Science, Lebanese University,
Beirut, Lebanon
4
Physics Department, Faculty of Science, Alexandria
University, Alexandria, Egypt
5
Accelerator Laboratory, Lebanese Atomic Energy
Commission, Beirut, Lebanon
Keywords GdBa
2
Cu
3
O
7-δ
· Nanoferrite ZnFe
2
O
4
·
Electron paramagnetic resonance · Number of spins
1 Introduction
The electron paramagnetic resonance (EPR) investigation
of high-temperature superconductors (HTSCs) serves as a
powerful tool to examine the magnetic origin and magnetic
parameters of HTSCs. Few EPR studies had been per-
formed for GdBa
2
Cu
3
O
7-δ
(Gd-123) unlike Y-123 which
was extensively researched. Alekseevskii et al. [1, 2] and
Garifullin [3] conducted EPR studies for GdBa
2
Cu
3
0
7-δ
with δ = 0.15 and 0.5. A single-line spectrum of Gd
3+
ions
was observed for all samples. EPR measurements showed a
metallic character for samples with δ = 0.5, while resistiv-
ity measurements showed a semiconducting behavior. This
led to a conclusion that the samples are heterogeneous con-
sisting of metallic and dielectric phases. The line shape of
the Gd
3+
EPR signal shows a noticeable deviation from a
Lorentzian shape. It was observed that the EPR signal con-
sists of two signals with nearly equal g values (g ∼ 1.99) but
with two different linewidths. For the first line, the linewidth
linearly depends on the temperature. For the second one,
the linewidth does not depend on the temperature and is
equal to 1000 Oe. These signals are determined by metallic
and dielectric components, respectively. Single crystals of
Gd-123 were investigated by EPR measurements before and
after grinding at different temperature ranges (4–300 K) by
Bejjit and Haddad [4]. The results showed that the grinding
of the single crystal eliminated the skin effect and changed
the EPR line from asymmetrical to symmetrical. EPR mea-
surements were carried out for GdBa
2
(Cu
1-x
M
x
)
3
O
7-δ
(M = Fe, Co, Ni, and Zn) samples [5]. The linewidth of
Fe- and Co-substituted samples increased remarkably with