Charge, orbital, and magnetic order in Nd0.5Ca0.5MnO3

In the manganite Nd0.5Ca0.5MnO3, charge ordering occurs at a much higher temperature than the antiferromagnetic order (T-CO=250 K, T-N=160 K). The magnetic behavior of the phase T-N<T<T-CO is puzzling: its magnetization and susceptibility are typical of an antiferromagnet while no magnetic order is detected by neutron diffraction. We have undertaken an extensive study of the crystallographic, electric, and magnetic properties of Nd0.5Ca0.5MnO3 and established its phase diagram as a function of temperature and magnetic field. The charge disordered paramagnetic phase above T-CO presents ferromagnetic correlations. An antiferromagnetic charge exchange phase prevails below T-N, With complete charge and orbital ordering. In the inter mediate temperature range, charge ordering occurs while orbital ordering sets in progressively, with no magnetic order. Strong magnetic fields destroy the charge ordered phases in a first-order transition towards a ferromagnetic state.