A 57Fe Mössbauer study of charge ordering and phase separation in the rare-earth manganates, Nd0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3

Mössbauer studies of 2% 57Fe-doped Nd0.5Ca0.5MnO3 and Nd0.5Sr0.5MnO3 have been carried out over the 4.2–300K range after ensuring that such doping does not change their basic properties. The charge-ordering transition in these manganates is marked by abrupt changes in the quadrupole splitting. In the case of Nd0.5Ca0.5MnO3, two phases manifest themselves on cooling below the charge-ordering transition temperature. The evolution of the spectra as a function of temperature shows that long-range magnetic order does not occur sharply. The observed evolution with temperature is different in the two materials studied. In Nd0.5Ca0.5Mn0.98 57Fe0.02O3, it resembles that of a disordered magnetic material, whereas the temperature dependence of line shape of Nd0.5Sr0.5Mn0.98 57Fe0.02O3 is typical of a superparamagnetically relaxed magnetic system. Although both the manganates show well-resolved magnetic hyperfine spectra at 4.2K, the lines are slightly broad indicating possible coexistence of phases at low temperatures. A weak paramagnetic signal is also seen in the spectra of both the manganates at 4.2K.