Williamson-Hall technique for magnetic cooling in nanosized manganite LaNi_0.25Mn_0.75O₃ and ferrite LaNi_0.25Fe_0.75O₃

We addressed the physical characterisation and synthesis of both manganite LaNi_0.25Mn_0.75O₃ (LNM) and ferrite LaNi_0.25Fe_0.75O₃ (LNF) nanomaterials. Both samples were indexed to the orthorhombic structure with Pbnm (62) a space group. Scherrer method, Williamson-Hall technique, and Scanning Electron Microscopy (SEM) images prove that the materials are nano-sized. XPS measurements were investigated to study the structure of these materials. Magnetic data of the LNM system illustrate a Curie temperature at around T_C = 221 K presenting a ferromagnetic to paramagnetic transition (FM/PM) while heating the sample. For the LNF sample, a blocking temperature T_B = 250 K defining a transition from the superparamagnetism (SPM) to the blocked state of the ferromagnet/spin-glass (SG) order till attaining the irreversibility temperatures T_irr = 390 K where the FM state starts. It is demonstrated how both systems differ significantly via the relative cooling power (RCP) values confirming the important effect of the Mn compared to the Fe in magnetic refrigeration. The RCP (1 T) = 44.107 J/kg and RCP (7 T) = 374.257 J/kg for the LNM sample vs. RCP (1 T) = 1.047 J/kg and RC (7 T) = 19.543 J/kg for the LNF compound. The evolution rate at 7 T is around 1815% making the difference very clear and presenting the LNM system as a very suitable magnetic refrigerant.