Charge ordering, internal structural parameters, and magnetic susceptibility of Nd2/3Ca1/3MnO3:: driving forces of a phase transition

The temperature dependences of the long diagonals d(Mn-O) of the MnO6 octahedron and the magnetic susceptibility chi of Nd2/3Ca1/3MnO3 in the temperature interval 100-290 K are investigated. The functions d(Mn-O)(T) and chi(T) are found to have anomalies in the charge-ordering range (T-co approximate to 212 K). The sharp decrease of the diagonal d(Mn-O2s) agrees with phase-transition notions, according to which the spatial modulation of the charge density is due to the modulation of the Mn-Mn bond lengths. The most likely driving forces of the transition are the Peierls lattice instability and Jahn-Teller stability of the MnO6 octahedron at the Mn3+ ions. The hysteresis of the temperature dependence chi(7) in the paramagnetic region shows indirectly that structural phase separation occurs together with the transition. The parameters of the function chi(7) indicate that ferromagnetic clusters consisting of one, two, or three ion pairs Mn3+-Mn4+ form in the system in the temperature intervals 274 K <= T <= 290 K, 224 K <= T <= 252 K, and 130 K <= T <= 198 K, respectively. (c) 2008 American Institute of Physics.