Magnetic Field-Induced Phase Transition and Weak Ferromagnetism in Nonsuperconducting Optimally Doped PrBCO Cuprate

In this letter, we report anomalous magnetic properties in high dc magnetic fields
H
up to 11 and 16 T from 1.35 up to 20 K on PrBa
₂
Cu
₃
O
_6.95
(PrBCO
_6.95
) cuprate ceramic. Significant magnetic-field effects are revealed in the derivative of the magnetization
M
(
T
) versus
T
using two sets of values of
H
selected in the range of 2.5–9.5 T. Anomalies are observed at the low-critical point
T
_cr
= 4–5 K, in the region of the spin reorientation phase transition temperature
T
₂
= 10.5 K, and around the Néel temperature of the antiferromagnetic ordering of the Pr
³⁺
sublattice
T
_N
= 14 K. Using Arrott plot analysis, we identified weak field-induced phase transitions at two critical fields,
H
_cr1
(
T
) ∼ 3.3 T and
H
_cr2
(
T
) ∼ 7.5 T, whose associated transition lines exhibit an almost temperature-independent behavior in the range 1.35 K-
T
₂
, and seem to vanish in the vicinity of
T
_N
. When
T
decreases from 20 K, an increase occurs in the derivative of the magnetization
M
(
H
) versus
H
for 0.5 T <
H
< 1 T, as well as in the differential susceptibility
χ
_d
(
T
) versus
T
where a shape change occurs when crossing
T
_cr
. The spontaneous magnetization
M
_S
(
T
), which was deduced by extrapolation to zero-field from the field-linear regime up to 2 T, shows an inverse variation with
T
and a shape change when crossing
T
_N
and
T
₂
. These features, which are taken as evidence for an additional weak ferromagnetic-like component that survives above
T
_N
, result from the significant role of the Pr-Cu(2) magnetic coupling.