Magnetocaloric effects and critical behavior of La0.65Ca0.35−xGdxMnO3 (0≤x≤0.15).

In this study, we investigate the magnetocaloric effects (MCE) and critical behavior of Gd-doped La 0. 6 5 Ca 0. 3 5 − x GdxMnO3 (x = 0 , 0. 1 0 , 0. 1 5) polycrystalline materials. Our results reveal excellent MCE in the Gd-doped samples. Under a magnetic field of 7 T, the full-width at half maximum (Δ T FWHM ) increases from 41 K (x = 0. 0 0) to 121 K (x = 0. 1 0) and 112 K (x = 0. 1 5). Additionally, the refrigerant capacity (RC) is enhanced by 149% and 145% at x = 0. 1 0 and x = 0. 1 5 , respectively, compared to the parent phase. We propose that these improvements can be attributed to the introduction of Gd 3 + ions, which possess smaller ionic radii. This reduction in the average A-site ionic radius weakens the double exchange (DE) interactions, resulting in a more continuous phase transition within the system. Supporting this view, we observe a decrease in magnetization strength after doping, a reduction in Curie temperature ( T C) from 250 K (x = 0. 0 0) to 134 K (x = 0. 1 0) and 130 K (x = 0. 1 5) and a transformation from a first-order to a second-order phase transition in the doped samples. To characterize the critical behavior of the phase transition in the doped samples, we employ the K-F method. The obtained critical exponents for x = 0. 1 0 and x = 0. 1 5 are β = 0. 3 8 0 ± 0. 0 0 6 , γ = 1. 3 2 3 ± 0. 0 0 3 , δ = 4. 4 8 2 ± 0. 0 0 5 and β = 0. 4 7 7 ± 0. 0 0 8 , γ = 1. 0 8 3 ± 0. 0 0 4 , δ = 3. 2 7 0 ± 0. 0 0 2 , respectively. Furthermore, the calculation of the n values suggests a transition of the phase transition in the doped samples from short-range ordering to long-range ordering. [ABSTRACT FROM AUTHOR]