Effects of the Cu Doping on Critical Behavior of ${\rm La}_{0.7}{\rm Ca}_{0.3}{\rm MnO}_{3}$

We have studied the influence of the Cu-doping on the critical properties of a polycrystalline sample of La
_0.7
Ca
_0.3
Mn
_0.95
Cu
_0.05
O
₃
prepared by solid-state reaction. Analyses of static magnetization data in the vicinity of the ferromagnetic-paramagnetic phase transition based on the modified Arrott plot reveal critical parameters of T
_C
≈ 197.3 K, β = 0.49 ± 0.03 and γ = 1.04 ± 0.04. These parameters are in good agreement with a magnetic equation of state M(H, ε) = ε
^β
f±(H/ε
^β+γ
), where ε = (T - T
_C
)/T
_C
(the reduced temperature), f
₊
for T >; T
_C
and f_ for T <; T
_C
. Comparing with theoretical models, the critical exponents in our case are close to those expected for the mean-field theory. This reflects that the Cu doping leads to the second-order phase transition in La
_0.7
Ca
_0.3
Mn
_0.95
Cu
_0.05
O
₃
while the parent compound of La
_0.7
Ca
_0.3
MnO exhibits the first-order phase transition. Such the phenomenon is assigned to changes in structural parameters, Mn
³⁺
/Mn
⁴⁺
ratio, and magnetic interaction mechanisms caused by Cu dopants.