Domain orbital state in ferromagnetic insulating La$_{0.825}$Ca$_{0.175}$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$ compound

TL;DR

This study investigates the magnetic and orbital properties of a ferromagnetic insulating manganite using Mössbauer and EPR spectroscopy, revealing orbital disordering above 100 K and mean field behavior of hyperfine fields.

Contribution

It provides new insights into the hyperfine field behavior and orbital disordering in a specific ferromagnetic insulating manganite, contrasting with metallic regimes.

Findings

Hyperfine field follows mean field approximation in the insulating phase.

Orbital disordering occurs above approximately 100 K.

Spectra are similar despite differences in magnetic measurements.

Abstract

Using M\"ossbauer and EPR spectroscopy we have studied the insulating ferromagnetic La$_{1-x}$Ca$_x$Mn$_{0.99}$$^{57}$Fe$_{0.01}$O$_3$ ($x=0.175$) compound prepared in air and reduced atmosphere. The average hyperfine field follows a mean field approximation solution in contrast with the ferromagnetic metallic regime where it significantly deviates from the order parameter deduced from neutron diffraction data or mean field approximation. Although the magnetic measurements show remarkable differences between air prepared and reduced R samples the corresponding M\"ossbauer spectra are almost identical. The strong temperature dependance of the hyperfine field distribution at the $^{57}$Fe nucleus is related with the supertransferred magnetic field between ferric ion and the oxygen bridged six nearest-neighbor manganese ions. The sudden increasing of the width of the hyperfine field distribution above $T_B\approx 100$ K has been attributed to the orbital disordering occurring for $T>T_B$.