Appearance of Griffiths phase and the magnetocaloric effect in Pr- and (Pr, Bi)- doped ZnO nanoparticles

Abstract

We have investigated the effect of Pr and (Pr,Bi) doping on the structural, magnetic and magnetocaloric properties of ZnO. All the samples were prepared via the sol gel method. X-ray diffraction (XRD) analysis revealed that Pr and Pr,Bi introduction forms a secondary phase of Pr6O11 for Pr0.01Zn0.97O and Pr0.01Bi0.01Zn0.97O. According to the magnetic properties, our samples underwent a second order phase transition from ferromagnetic (FM) to paramagnetic (PM) at Curie temperature (TC).The deviation of the inverse curve of the magnetic susceptibility from Curie-Weiss law(CW) indicates the existence of a Griffiths phase(GP) for Pr0.01Zn0.97O and Pr0.01Bi0.01Zn0.97O. The magnetocaloric effect (MCE) was assessed using magnetic entropy change (ΔSM) which is basically determined from the magnetic field dependence of magnetization at different temperatures M(µ0H,T) near TC. The maximum magnetic entropy change |ΔSMMax| and the relative cooling power (RCP) were respectively 1.36, 1.34 and 1.17 J/kg.K and 107, 109 and 86 J/kg at a field change of 5T for ZnO, Pr0.01Zn0.97O and Pr0.01Bi0.01Zn0.97O. These values compared favorably with some other reported materials, making our samples promising candidates for magnetic refrigeration.