Modification of the order of the magnetic phase transition in cobaltites without changing their crystal space group

Abstract

It has been found that GdBa1-xSrxCo2O6-δ can exhibit consecutive magnetic transitions: antiferromagnetic-ferromagnetic (AFM-FM) transition followed by ferromagnetic-paramagnetic transition (FM-PM), which give rise to a coexistence of inverse and conventional magnetocaloric effect (MCE), respectively. In the pristine compound (x = 0), its AFM-FM transition is shown to belong to a first-order phase transition and the FM-PM to a second-order type. Despite it is widely known that the properties of cobaltites are highly influenced by their oxygen content and type of doping carriers, in this work, further evaluation using magnetocaloric analysis (universal curve method and a quantitative criterion using magnetic field dependence of the magnetic entropy change) reveals that the first-order AFM-FM phase transition converts into a second-order character with just Sr doping of x = 0.1 (despite of having the same space group at room temperature and type of dopant carrier as x = 0), severely affecting its thermomagnetic properties. Moreover, the peaks of these two MCE span over a temperature range that is larger than those reported for cobaltite-type materials, making it closer to room temperature applications.