Magnetic Refrigeration Properties of ${\hbox {La}}_{0.8}\hbox {Ca}_{0.2}\hbox {Mn}_{0.99}{^{57}\hbox {Fe}_{0.01}}\hbox {O}_{3}$

The La_0.8Ca_0.2Mn_0.99 ⁵⁷Fe_0.01O₃ sample was prepared by sol-gel method. The crystallographic and magnetic properties of La_0.8Ca_0.2Mn_0.99 ⁵⁷Fe_0.01O₃ have been studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mossbauer spectroscopy measurements. The crystal structure of La_0.8Ca_0.2Mn_0.99 ⁵⁷Fe_0.01O₃ was found to be orthorhombic (Pnma) structure with lattice constants a_o=5.486 Aring, bo=7.761Aring, and c_o=5.510 Aring at room temperature. The Curie temperature (T_c) is determined to be 160 K by zero field cooled (ZFC) magnetization curve under 5 kOe applied field. The maximum value of magnetic entropy changes, |DeltaSM| is 1.25 J/kgldrK at 157 K under 13 kOe applied field. Mossbauer spectrum at 4.2 K was fitted with two independent magnetic components of the magnetic hyperfine fields H_f,1=526 kOe and H_f,2=501 kOe. Mossbauer spectra show that the two well-resolved sextets show nearly equal intensities between them without any external fields. This unusual phenomenon provides direct evidence of the two-phase character of the metallic state in the mixed valence state of La_0.8Ca_0.2Mn_0.99 ⁵⁷Fe_0.01O₃ powder.