We investigated the magnetic and magnetocaloric properties of Gd_100-xCo_x ( $x$ = 40 to 56) thin films fabricated by the sputtering technique. Under an applied field change $\Delta H=20\mathrm{kOe}$ , the magnetic entropy change $(\Delta S_m)$ decreases from 2.64 Jkg⁻¹K⁻¹ for $x$ = 44 to about 1.27 Jkg⁻¹K⁻¹ for $x$ = 56. Increasing the Co concentration from x = 40 to 56 shifts the Curie temperature of Gd_100-xCo_x ( $x$ = 40 to 56) thin films from 180 K toward 337 K. Moreover, we extracted the values of critical parameters T_c, β, γ, and δ by using the modified Arrott plot methods. The results indicate the presence of a long-range ferromagnetic order. More importantly, we showed that the relative cooling power (RCP), which is a key parameter in magnetic refrigeration applications, is strongly enhanced by changing the Co concentration in the Gd_100-xCo_x thin films. Our findings help pave the way toward the enhancement of the magnetocaloric effect in magnetic thin films.

The structural, electronic, and magnetic properties of bismuth ferrite (BiFeO₃) and Bi₂Fe₄O₉ nanostructures were investigated using Density Functional Theory (DFT) within the Generalized Gradient Approximation (PBE-GGA) plus U approach. The PBE-GGA + U calculations predict band gaps of 2.4 eV for BiFeO₃ and 2.3 eV for Bi₂Fe₄O₉, closely aligning with experimental data. The analysis of partial and total density of states reveals strong hybridization between iron 3d and oxygen 2p states, with a significant contribution from Fe 3d orbitals in both structures. Additionally, nanostructure and crystal symmetry are crucial in influencing the magnetic properties of BiFeO₃ and Bi₂Fe₄O₉. Our calculations indicate that the antiferromagnetic phase is energetically more favorable than the ferromagnetic phase in both materials.