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

Abstract

Using Mössbauer 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 Mössbauer 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 $T>T_B$.