Coexistence of short- and long-range ferromagnetic order in La0.7Sr0.3Mn1-xCoxO3 compounds

Polycrystalline La0.7Sr0.3Mn1-xCoxO3 (x = 0.0-1.0) samples were synthesized by solid-state reaction. Structural and magnetization studies reveal the replacement of Co for Mn in La0.7Sr0.3Mn1-xCoxO3, and the decrease of the Curie temperature (T-C) from 360K (for x = 0) to 224K (for x = 1). Positive slopes observed in the H/M versus M-2 curves prove all the samples undergo a second-order magnetic phase transition. By analysis of the M(H) data at temperatures around T-C using the Kouvel-Fisher method, we obtained the values of critical parameters (T-C, beta, gamma, and delta). The results suggest an existence of short-range FM order in the sample x = 0 with beta = 0.377. Meanwhile, for the case of Co-doped samples, their beta values in the range of 0.403-0.457 indicate a coexistence of short and long-range FM order. This means that Co-doping favors establishing FM long-range order in La0.7Sr0.3Mn1-xCoxO3. From M(H) data, we have also determined the magnetic entropy change (Delta S-m) for the samples. We have found that the Delta S-m(T) curves for different applied fields are collapsed onto a universal curve by normalizing the Delta S-m(T) curves to their respective maximum value Delta S-max (i.e., Delta S-m(T)/Delta S-max) and rescaling the temperature axis above and below T-C with theta = (T - T-C)/=(T-r - T-C), where T-r is the reference temperature. (C) 2015 AIP Publishing LLC.