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
_0.8
Ca
_0.2
Mn
_0.99

⁵⁷
Fe
_0.01
O
₃
sample was prepared by sol-gel method. The crystallographic and magnetic properties of La
_0.8
Ca
_0.2
Mn
_0.99

⁵⁷
Fe
_0.01
O
₃
have been studied using X-ray diffraction (XRD), vibrating sample magnetometer (VSM) and Mossbauer spectroscopy measurements. The crystal structure of La
_0.8
Ca
_0.2
Mn
_0.99

⁵⁷
Fe
_0.01
O
₃
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
_0.8
Ca
_0.2
Mn
_0.99

⁵⁷
Fe
_0.01
O
₃
powder.