Investigation of the magnetocaloric effect and the critical behavior of the interacting superparamagnetic nanoparticles of La0.8Sr0.15Na0.05MnO3

Abstract

We report on structural, magnetic properties of Na-doped La0.8Sr0.15Na0.05MnO3 (LSNMO) nanoparticles (NP) with size about 50 nm elaborated via sol-gel route. The chemical composition was verified using the energy dispersive X-ray analysis (EDAX) and by X-ray photoelectron spectroscopy (XPS). Magnetic characterizations demonstrate that LSMNO exhibits a coexistence of interacting superparamagnetic (ISPM) phase with blocking temperature TB = 194 K and a ferromagnetic phase with Curie temperature TC = 255.5 K. At low temperatures, the SPM state undergoes a collective freezing state at Tf = 46 K. the high-temperature regime (well above TC) reveals that NP-LSNMO has a strengthened Griffiths-like phase compared to their bulk counterpart. An itemized investigation of the critical behavior of the material was carried out in the vicinity of TC. The critical exponents [β = 0.546(7), γ = 0.972(6), and δ = 2.94 (5)] were found to be in close agreement with of the mean-field theory. The maximum magnetic entropy change (−ΔSMpk) is about 1.41 Jkg-1 K-1 and the refrigeration capacity (RC) is 288 Jkg-1 for a field change of 5 T at T = 215 K. This magnetocaloric response is reasonably high for nanomaterials and, together with its cost-effectiveness, makes NP LSMNO a potential candidate material for active magnetic refrigerators. Besides, the ISPM properties are desirable for hyperthermia applications. Our findings suggest that the magnetic inhomogeneity and the dipolar interaction between the SPM and FM phases in the range TB<T<TC are crucial factors in determining the magnetic properties of NP-LSNMO.