Observation of Griffiths phase, critical exponent analysis and high magnetocaloric effect near room temperature at low magnetic field in V-doped La0.7Sr0.3MnO3

Abstract

We report on observation of the Griffiths phase (GP), high magnetocaloric properties at low magnetic fields and temperature-dependent critical exponents of La0.7Sr0.3V x Mn1−x O3 (x = 0, 0.05 and 0.1) perovskite bulk materials. The Curie temperature (T C) of pure La0.7Sr0.3MnO3 (LMSO) is seen to be 368.7 K and decreases toward room temperature (RT) (342.2 K) by 10 mol% V doping at the Mn site. V doping leads to an enhancement in magnetic entropy change (−ΔS M) from 1 J kg−1 K−1to 1.41 J kg−1 K−1. V doping at a Mn site leads to the formation of GP, a magnetic disorder due to the coexistence of a paramagnetic (PM) matrix and short-range ferromagnetic (FM) clusters. X-ray photoelectron spectroscopy analysis confirms the presence of mixed-valence V4+/V5+along with Mn3+/Mn4+ ions contributing to various double exchange interactions. The natures of phase transitions and magnetic interactions are analyzed by evaluating critical exponents δ, β, and γ. All the samples show second-order FM to PM phase transition, confirmed from the modified Arrott plots and critical exponent analysis carried out using the Kouvel–Fisher method. The enhancement in magnetic entropy change along with the decrease in Curie temperature toward RT by V doping in the LMSO oxides indicates the possible application of these materials in magnetic refrigeration at low magnetic fields.