Effect of lanthanum-deficiency on structural, magnetic and magnetocaloric properties of $${\text{L}}{{\text{a}}_{0.5}}{\text{S}}{{\text{r}}_{0.5}}{\text{Co}}{{\text{O}}_3}$$

Lanthanum-deficient mixed-valence cobaltite of nominal formula \({\text{La}}_{{0.5 - x}} \Box_{x} {\text{Sr}}_{{0.5}} {\text{CoO}}_{3};(0 \le x \le 0.2)\) has been investigated for its structural, magnetic, and magnetocaloric properties. Our samples were synthesized using the sol–gel method. X-ray diffraction analysis showed that all samples crystallized in the rhombohedral symmetry with \(R\bar {3}c\) space group. Magnetization measurements versus temperature under different magnetic fields indicate that the samples undergo a paramagnetic to ferromagnetic phase transition. The Curie temperature seems to decrease with increasing lanthanum vacancy, but is still higher than that of the stoichiometric compound. Under a magnetic field of 5 T, the magnetic entropy change maximum \(\left| {\Delta S_{M}^{{{max} }}} \right|\) reaches a value of 1.63 J kg−1 K−1 for x = 0.2, which corresponds to a value of 139 J kg−1 for the relative cooling power. Furthermore, the magnetic entropy change sensitivity to the magnetic field was checked using the local exponent \(n\left( {T,{\text{ }}{\mu_0}H} \right).\)