Microstructure, magnetocaloric effect and near tricritical mean-field critical behavior of La0.67Ca0.33-xKxMnO3 porous nanospheres prepared by solvothermal method

In this study, La0.67Ca0.33-xKxMnO3 porous nanospheres with K+ replacing Ca2+ were prepared by the solvothermal method. The microstructures, surface valence, magnetic properties, magnetocaloric effect and critical parameters of magnetic phase transition were investigated. The structural characterization showed that the grain size of La0.67Ca0.33-xKxMnO3 exhibited an increasing and then decreasing trend with the increase of K+ doping. The magnetic testing of La0.67Ca0.33-xKxMnO3 revealed that K+ doping increased the phase transition temperature of the system and modified the magnetic interactions before and after the phase transition temperature. As a result, the critical behavior of the magnetic phase transition was affected with K+ doping. When x = 0.05 and 0.1, the critical behavior of samples exhibited similarities to the tricritical mean-field model. Furthermore, K+ doping enhanced the magnetic refrigeration ability of the system, with the maximum magnetic entropy reaching 5.99 J/kg K for K-0.05. [Display omitted] •La0.67Ca0.33-xKxMnO3 porous nanospheres were prepared by doping K+ in solvothermal process.•The critical behavior of La0.67Ca0.33-xKxMnO3 was close to the tricritical mean-field when x = 0.05 and 0.1.•The critical parameters were calculated using multiple criticality models and two fitting methods of MAP and KF.•The |-ΔSMmax| of La0.67Ca0.33-xKxMnO3 porous nanospheres were enhanced by adjusting the doping amount of K+.