J Low Temp Phys (2012) 166:218–230
DOI 10.1007/s10909-011-0413-6
New Magnetic Phase Transitions in the Tetragonal
Compounds PrBa
2
Cu
3
O
6+x
at Low Temperature
Walid Younsi · Mahieddine Lahoubi ·
Mohamed-Larbi Soltani
Received: 23 October 2010 / Accepted: 4 October 2011 / Published online: 9 November 2011
© Springer Science+Business Media, LLC 2011
Abstract The anomalous magnetic properties of Pr ions in the PrBa
2
Cu
3
O
6+x
sys-
tem are investigated at low temperature. Measurements of the specific heat C
P
(T ) and
the magnetic susceptibility χ(T) are performed on ceramic samples in the tetragonal
structure with x = 0.44 and x = 0. Two new magnetic transitions are observed below
the Néel temperature of the Pr antiferromagnetic ordering T
Pr
N
∼ 9–10 K. The first one
is observed at the low-critical temperature T
cr
∼ 4–5 K and the second one is observed
at T
Pr–Cu
2
∼ 6–7 K, respectively. Assuming that C
P
(T ) can be used to represent the
Pr contribution to the specific heat C
P
(T ), the data are well fitted for T<T
cr
by us-
ing the development of C
P
(T )/T = A(T
2
)
−3/2
+ γ + M(T
2
)
1
+ m(T
2
)
2
. The
values of the electronic coefficient γ are found much lower than all previous results
obtained in compounds of the orthorhombic structure, and this is, in good agreement
with the insulating character of our non-superconducting samples. The high values
obtained for the coefficient M, permits us to confirm the existence of strong Pr–Pr ex-
change interactions. Some non-linear effects attributed to the values of the coefficient
m are revealed and discussed in terms of the previous Pr–Cu coupling with a spin
reorientation phase transition of both spin sublattices around T
Pr–Cu
2
. The appearance
of a weak ferromagnetic tendency in the magnetic susceptibility analysis below T
cr
,
could be associated with the reordering of the Pr subsystem.
Keywords Cuprates · Antiferromagnetics · Specific heat · Magnetic susceptibility ·
Magnetic phase transitions · Spin reorientation
W. Younsi · M. Lahoubi ( ) · M.-L. Soltani
Department of Physics, Faculty of Sciences, Badji Mokhtar-Annaba University, PO Box 12, 23000
Annaba, Algeria
e-mail: mlahoubi@hotmail.fr
W. Younsi
e-mail: walidyounsi@yahoo.fr
M.-L. Soltani
e-mail: ml_soltani@yahoo.com