Potassium doping induced changes of magnetic and magnetocaloric properties of La0.78Cd0.22−xKxMnO3 (x = 0.00, 0.10, 0.15 and 0.20) manganites

In this paper, we have studied the effect of K substitution on the structural, magnetic and magnetocaloric (MCE) properties of the perovskite manganites La0.78Cd0.22−xKxMnO3 (x = 0.00, 0.10, 0.15 and 0.20) which were prepared by standard solid-state reaction method. The phase purity of prepared samples were verified by analyzing the X-ray diffraction patterns and shows that all compositions crystallize in the rhombohedral structure with the R3‾c space group. The zero field cooled (ZFC) and field cooled (FC) magnetization measurements reveal that all the samples undergo a paramagnetic-ferromagnetic (PM-FM) phase transition and the transition temperature is found to increase from 202 K for x = 0.00 to 326 K for x = 0.20. Magnetic entropy change (ΔSM) was also studied which reaches a maximum values of 3.6, 4.86, 5.66 and 5.98 J/kgK at 5 T for x = 0.00, 0.10, 0.15 and 0.20 composition, respectively. However, the relative cooling power (RCP) decreases with increasing K content from 274 (x = 0.00) to 216 (x = 0.20) J/kg for 5 T due to the decrease of full width at half maximum of ΔSM curves with increasing K dopant. All the studied samples exhibit a second-order magnetic phase transition at TC. The field dependence of the magnetic entropy change curves show a power law dependence, ΔSMmax∞Hn, around the TC. The obtained n values are 0.89, 0.82, 0.86 and 0.75 for x = 0.00, 0.10, 0.15 and 0.20 respectively, confirms not only the invalidity of the mean field model. Thus, the calculated 'n' values corroborate the absence of long range magnetic order and suggest the existence of magnetic inhomogeneities in all the samples reported here.