Critical Behavior and Magnetocaloric Effect of Pr1-xSrxCoO3

The modified Arrott plot method was used to analyze magnetic-field dependences of magnetization, M(H), for two polycrystalline samples Pr
_1-x
Sr
_x
CoO
₃
with x = 0.4 and 0.5. The analyses determined the values of critical parameters T
_C
≈ 204 K, β = 0.654 ± 0.016, y = 1.11 ± 0.009, and δ = 2.70 ± 0.009 for x = 0.4, and T
_C
≈ 218 K, β = 0.495 ± 0.004, y = 0.991 ± 0.003, and δ = 2.86 ± 0.009 for x = 0.5. With these critical values, the M(H) data around the T
_C
of the samples fall into two universal branches of a scaling function M(H, ε) = |ε|
^β
f
_±
(H/|ε|
^β+y
), where ε = (T-T
_C
)/T
_C
, and f
₊
for T > T
_C
and f_ for T <; T
_C
. Here, the T
_C
increase with the increasing Sr content is ascribed to an increase of ferromagnetic (FM) double-exchange interaction pairs of Co
³⁺
-Co
⁴⁺
, and to the β change from 0.654 (for x = 0.4) to 0.495 (for x = 0.5). This corresponds to the change in FM interactions from short-range to nearly long-range FM orders. Based on the M(H) data, we also determined the magnetic-entropy change, which reaches a maximum value (|ΔS
_max
|) around the T
_C
; |ΔS
_max
| ≈ 1.9 and 2.2 J/kg · K for x = 0.4 and 0.5, respectively, for a magnetic field change ΔH = 50 kOe. The relative cooling power thus increases from 52 J/kg (for x = 0.4) to 84 J/kg (for x = 0.5). In particular, field dependences of the magnetic-entropy change (ΔS
_m
) obey a power function |ΔS
_m
(H)| ∝ H
ⁿ
, where the magnetic-ordering parameter (n) slightly decreases from 0.75 for x = 0.4 to 0.70 for x = 0.5.