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In this paper, the effect of A-site ionic disorder (σ2) on the structure, magnetic and magnetocaloric properties in La 0.85-x Nd x Ag 0.15-y K y MnO 3 have been investigated. X-ray diffraction analysis using Rietveld refinement shows that the crystal structure of the perovskite manganites changes from rhombohedral (space group R3 ͞C) to orthorhombic (space group Pnma) structure with the increasing in σ2. Magnetization measurements showed that, upon increasing σ2, ferromagnetic double exchange interaction of the perovskite manganites diminishes, and as a result, Curie temperature (T C) of the samples decrease linearly. The inverse of susceptibility shows a downturn with decreasing temperature before T C indicating the existence of the Griffiths phase for La 0.62 Nd 0.23 Ag 0·099 K 0·051 MnO 3 (σ2 = 0.004). The magnetic phase transitions of all the samples are belongs to second order transition. [ABSTRACT FROM AUTHOR]

The effects of the substitution of La3+ by smaller rare-earth ion Nd3+ on the structural, magnetic and magnetocaloric properties of La 0.67-x Nd x Ca 0.13 Ba 0.2 MnO 3 (x = 0.02, 0.06, 0.1) manganites prepared by solid state sintering technology have been investigated. X-ray diffraction analysis shows that the x = 0.02 sample crystallizes in the rhombohedral structure with R 3 ¯ c space group symmetry and the x = 0.06, 0.1 samples belong to the orthorhombic structure with Ibmm space group. The Rietveld refinements for all samples were carried out to investigate on the crystal structures of the samples. Thermomagnetic measurements indicate that all the samples exhibit a magnetic transition from ferromagnetic to paramagnetic phase with increasing temperature. The Curie temperature T C systematically decreases from 308 K to 280 K with the accumulation of Nd concentration. Critical analysis demonstrates that the estimated critical exponents β, γ and δ are between the theoretically predicted values for 3D-Ising and mean-field theory models for all samples. The magnetic entropy change has been calculated from the isothermal magnetization measurements as a function of the applied magnetic field at various temperatures near T C. The maximum magnetic entropy change -ΔS max under an applied magnetic field of 1.6 T was found to be 3.06, 2.92 and 2.48 J kg−1 K−1 respectively for x = 0.02, 0.06 and 0.1 samples. This indicates that these manganites are remarkably potential functional materials working as magnetic refrigerants near room temperature. • The crystal structure of samples transform from rhombohedral to orthorhombic with the accumulation of Nd concentration. • The Curie temperature T C decreases from 308 K to 280 K with increasing Nd composition. • The estimated critical exponents β, γ and δ are in between the theoretically predicted values for 3D-Ising and mean-field theory models for all samples. • The largest value among the maximum magnetic entropy change −ΔS max of all samples under applied magnetic field of 1.6 T were found to be 3.06 J kg−1 K−1 for x = 0.02. [ABSTRACT FROM AUTHOR]