STRUCTURAL AND MAGNETIZATION STUDY OF THE COMPOUND PrBaCuO

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STRUCTURAL AND MAGNETIZATION STUDY OF THE COMPOUND
PrBa
2
Cu
3
O
7
-
δ


R. BENREDOUANE
1
, A. HARAT
1
, S. BELKAHLA
1
, M. GUERIOUNE
1







1
Laboratoire d’Etude des Etat Condensés, Université Badji Mokhtar, Annaba, Algérie

e
-
mail

:
rabab212002@yahoo.fr




Abstract

-

The compound PrBa
2
Cu
3
O
7
-
δ
(Pr123) present a lot of anomalous in structural and magnetic
properties, though it is isostructural to R123 superconducting compounds but it exhibits a semiconductor
behaviour.

This work
, we report the elaboration procedure of this compound by solid state reaction method and we present
their structural and magnetic properties


Keywords
-

superconduvtivity, Pr123, magnetization, magnetic susceptibility.


I
-

INTRODUCTION


Superconductivity
with Tc above 90 K was observed for almost orthorhombic RBa
2
Cu
3
O
7

(R123, R = Y and rare earth element). The anomalous member is the compound PrBa
2
Cu
3
O
7
-
δ

(Pr123) that does not exhibit superconductivity and shows semiconductivity behaviour down
to very low temperature, with very large electrical resistivity (10
7

Ω.cm)[1]. Furthermore, Pr
+3

moments order antiferromagnetically with high T
N

(Pr) ranging fro
m 9 K to 20 K depending
on oxygen content, which is much higher than T
N
(R) of the other magnetic rare earth
compounds with a maximum of 2,2 K for the superconducting compound Gd123.

Several mechanisms have been proposed to explain the dramatic suppression
of
superconductivity in Pr123, the most one being hole localization (trapping) which have been
proposed on the base of strong hybridisation between Pr
4f

orbitals and O
2p
π

ones in the CuO
2

bilayer, this hybridisation may be responsible of the relatively high ordering temperature of
the Pr moments in Pr123.

Recently, inhomogeneous superconductivity was reported by several groups [2
-
4] in this
system where the c
-
axis lattice

parameter is considerably longer than the one usually observed
in Pr123. Arguments for the appearance of superconductivity pointed in the direction that the
substitution of Ba for Pr and the elongation of the Pr
-
O atomic distance.

So, it seems that Pr123

is very sensitive to synthesis conditions. The aim of this paper is the
study of the magnetic properties in relation with the structural properties of powder sample
elaborated by solid
-
state reaction method under well
-
controlled conditions.


II
-

EXPERIMEN
TAL PROCEDURE


PrBa
2
Cu
3
O
7
-
δ

samples were prepared by the conventional method of solid
-
state reaction,
starting from commercial powders of Pr
6
O
11
, BaCO
3
, and CuO. The no reacted sample was
calcined at 800°C for 8h. The reacted sample was than powdered in ag
ate mortar with the
pestle and heated in air at 920°C for 24 h. This process was repeated twice, and then the
sample was cooled slowly to 500°C, kept at this temperature for 10h and then cooled to room
temperature. In order to compare with structural prope
rties of the homologous compound, we
have also elaborated an Y123 sample following the same procedure.

0
20
40
60
80
100
0
20
40
60
80


-1
linear fit


1/

(mol/emu)
T(K)

Figure 3
\

Inverse
magnetic susceptibility


X
-
ray diffraction data was collected in the interval [20°
-
60°]. Susceptibility and
magnetization measurements were made in the temperature range of 4
-
30
0K in applied d.c
field of 0,2 T.


III
-

RESULTS AND DISCUSSION


The XRD pattern (Fig1), show that the sample has the tetragonal phase with space
groupe P4/mmm. The XRD pattern (Fig 1), shows that the sample has the tetragonal single
phase Pr123 with space
group P4/mmm. The lattice parameters are :

a= 3,910 Å and c= 11,638 Å which are in good agreement with the results of Uma et al [5].
The oxygen content was estimated using results of the variation of the lattice parameters
versus oxygen content and estima
ted to be O
6,15
. Some traces of secondary phase Pr
2
CuO
4

were found.




















Magnetic susceptibility

is shown on figure 2.


(T)


increases continuously on cooling
whereas Pr
3+

antiferromagnetic ordering temperature
T
N

appears only as a small
kink, and is
rather dete
r
mined from the deriv
a
tive d

(T)/dT (see the insert). For our underdoped sample
we find T
N

= 14.5 K.















0
50
100
150
200
250
300
0.00
0.04
0.08
0.12
0.16
0.20
H = 0.2 T



(emu / mol)
T (K)
0
10
20
30
40
50
60
70
80
T (K)
d

/dT
T
N
= 14.5 K




Figure 2
\

Magnetic susceptibility and it’s
摥物癡瑩癥


20
25
30
35
40
45
50
55
60
*
Pr
2
CuO
4
*
212
213
115
203
104
005
112
200
114
113
101
110
100


Intensity
(a.u)
2

(°)

c楧u牥‱
y

塒䐠灡瑴e牮r⁴桥⁐爱㈳


Below T
N

the susceptibility continue to decrease. Although the sample is oxygen deficient,
it’s T
N

is much higher th
an the other tetragonal Pr123 reported by several groups such as in
Guillaume et al [6]. Indeed, for underdoped Pr123, T
N

ranges between

9.5 K and 11 K. However, the value of T
N

for orthorhombic samples (oxygenated ones) is
between 15 K and 20 K [1, 6].
We want to point out that our Y123 sample elaborated under
the same conditions has the orthorhombic structure and then is oxygen reach.

On figure 3
,
the inverse of susceptibility is plotted
as a function of temperature

versus and one
can see that f
or T > T
N
,

(T)
is well fitted by Curie
-
Weiss law :




=

o

+ C/(T
-

p
)


where
χ
0

is the temperature
-
independent term and C is the Curie constant,

p

is the
paramagnetic temperature.From our fit we found that
χ
0
= 11.10
-
4

emu/mole,
C
=1,43
emu.K/mole and

p

=
-
8,79
K, these results are in good agreement with the ones find by Uma
et al in underdoped single crystal [7].

In order to see oxygen influence on T
N

, we have oxynated our sample by heating to 500 C°
and cooling slowly to room temperature under flowing oxygen o
ver several hours.
Surprisingly, susceptibility measurements do not show a change of T
N

which stills at 14.5 K;
however we have noted a lowering of susceptibility.

We have also measured the isothermal magnetization of the sample at different temperatures
b
elow 15K.


















The obtained results are shown in fig 4. At all temperatures the M(H) dependencies are nearly
linear and the magnetic anisotropy is more pronounced at lower temperatures, we can also
note that M never reaches saturation, even fo
r high fields.


IV
-

CONCLUSION


In conclusion, we can say that magnetic properties are very correlated to
crystallographic ones. For the Pr
3+

antiferromagnetic ordering temperature of our underdoped
sample, we find that it is comparable to oxygenated samp
les. Moreover it has not changed
when we oxygenate the sample, opening a question about oxygenation. Further, knowing that
T
N

is sensitive to Pr/Ba substitution [8], which seems to occur systematically in this
0
2
4
6
8
10
-1
0
1
2
3
4
5
6
7
8
4.5 K
7.5 K
6 K
3 K
10 K
1.6 K
15 K


M
(uem/mol)
H
(T)

Figure 4
\

Isothermal magnetization as a
function of magnetic field

compound, we have also to check for this subst
itution by SEM measurements. This may give
some explanation for T
N

value.

However the Curie
-
Weiss constant and the paramagnetic Curie temperature are in good
agreement with the result of underdoped systems. Other measurements have to be completed
to clarif
y this point.



V
-

REFERENCES


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