Electronic Structure and Magnetocaloric Effect of Sr-Doped SmCoO3 Perovskites

We present a study on the magnetic and magnetocaloric characters of Sm1-xSrxCoO3 (x=0.4-0.6) synthesized by solid-state reactions. Recorded M(T) data at H=100 Oe show an increase of the Curie temperature (T-C) from 143 K for x=0.4 to 153 K for x=0.5, but a higher x value (x = 0.6) reduces T-C to similar to 92 K. A singularity region sandwiched between the Griffiths and pure paramagnetic phases has been observed in x=0.4, but it becomes invisible at x=0.5 and 0.6. These properties are assigned to a competition between ferromagnetic and anti-ferromagnetic interactions induced by Co3+ and Co4+ ions. The Co3+/Co4+ mixed valence has been confirmed upon the analysis of Co K-edge x-ray absorption spectra. Using Maxwell's relations and M(H) data, we have calculated the absolute magnetic entropy change (vertical bar Delta S-m vertical bar). Around T-C, the maximum magnetic entropy changes (vertical bar Delta S-max vertical bar) of x=0.4, 0.5 and 0.6 are about 1.19, 1.22 and 0.81 J/kg K for H =50 kOe, respectively. The values of the relative cooling power are in the range of 58 - 93 J/kg. Our analyses also indicate all vertical bar Delta S-m (T, H)vertical bar data obeying the universal master curve as constructing the vertical bar Delta S-m vertical bar/vertical bar Delta S-max vertical bar vs. theta plots, where theta is defined as the reduced temperature. When considering exponential parameters N(T, H) and n associated with vertical bar Delta S-m(T, H)vertical bar and vertical bar Delta S-max(H)vertical bar, respectively, we have found their values are different from the mean-field theory value n = 2/3. These results prove the Sm1-xSrxCoO3 samples have the second-order nature and short-range magnetic order.