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

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