Improving the crystallinity and magnetocaloric effect of the perovskite La0.65Sr0.35MnO3 using microwave irradiation

Abstract

The use of microwave (MW) irradiation to assist the modified peroxide sol–gel synthesis of La_1−xSr_xMnO₃ was shown to 1) improve crystallinity and 2) enhance the magnetic susceptibility and magnetocaloric effect (MCE) of samples compared to those synthesised using the conventional method. The improvement in crystallinity of the samples synthesised using MW irradiation was evident in the structural characterisation conducted using SEM and XRD. Magnetic heating experiments on La_1−xSr_xMnO₃ (x = 0.25, 0.35 and 0.4) showed that for the MW-assisted method, the most suitable material for magnetic fluid hyperthermia applications was La_0.65Sr_0.35MnO₃. MW settings (time and power) were investigated in an attempt to further optimise the MCE. Increasing MW time settings used (10 min, 30 min and 2 hours) led to increased saturation temperatures (45.9 °C, 57.0 °C and 58.3 °C, respectively), with a linear relationship between the MW power settings used and the MCE also observed during the magnetic heating experiments. Specific absorption rates as high as 175 W g_Mn⁻¹ were achieved compared to the conventional maximum of 56 W g_Mn⁻¹ in previous work. The enhancement of MCE was ascribed to a greater core ferromagnetic contribution as a result of the improvement in the degree of crystallinity and magnetic susceptibility of the samples synthesised with MW irradiation.