Charge ordering at room temperature in Tb0.5Ca0.5MnO3

Tb0.5Ca0.5MnO3 has been studied by means of a.c. magnetic susceptibility, x-ray and neutron diffraction from 1.5 up to 330 K. This compound shows a structural transition at 299.7 K. Below this temperature a charge ordering state was observed by both x-ray and neutron diffraction measurements. The structure is orthorhombic at temperatures higher than 300 K, but at lower temperatures the patterns show new reflection peaks that can be accounted for in a monoclinic unit cell with stripes of Mn3+ and Mn4+ in the ac-plane. Moreover, the system orders antiferromagnetically at around 120 K giving rise to a magnetic structure of CE type. The magnetic susceptibility measurement clearly shows an anomalous behaviour at both transition temperatures. The charge ordering temperature for the Tb0.5Ca0.5MnO3 compound is the highest reported in the RE0.5Ca0.5MnO3 series (RE = rare earth). This is argued to be a consequence of the larger orthorhombic distortion produced in the unit cell by the lower size of Tb3+ ion.