Magnetocaloric Effect and Critical Behavior in a Disordered Ferromagnet La0.7Sr0.3Mn0.9Ti0.1O3

The critical phenomena around the Curie temperature (T
_C
) of a polycrystalline La
_0.7
Sr
_0.3
Mn
_0.9
Ti
_0.1
O
₃
were studied based on magnetic field and temperature dependence of magnetization. Using the modified Arrott plot method, we determined the critical parameters T
_C
≈234 K, β = 0.372 ± 0.012, γ = 1.171 ± 0.112, and δ = 4.15 ± 0.01. With these critical values, the M(H) data of the sample fall onto two universal branches of the scaling function M(H, ε) = |ε|
^β
f
_±
(H/|ε|
^β+γ
), where ε = (T - T
_C
)/T
_C
, and f
₊
for T > T
_C
and f
_-
for T <; T
_C
. This pointed to the existence of a short-range ferromagnetic (FM) order in La
_0.7
Sr
_0.3
Mn
_0.9
Ti
_0.1
O
₃
, which is attributed to FM clusters persisting in a wide temperature range, even above T
_C
. Electron-spin-resonance spectra affirmed the presence of the FM clusters at temperatures as high as T = T
_min
(≈1.3 T
_C
), above which the sample is completely paramagnetic. Based on the M(H) data, we also calculated the magnetic-entropy change (ΔS
_m
), which reached a maximum (|ΔS
_max
| ≈ 4.3 J/kg · K) around the T
_C
, corresponding to the relative cooling power of ~200 J/kg for a field change ΔH = 50 kOe. A linear relationship |ΔS
_max
(H)| ∝ H
ⁿ
is achieved with a local exponent n = 0.59 determined from n = 1+ (β - 1)/(β + γ), indicative of a short-range FM system.