A possible origin of colossal magnetoresistance in charge-ordered manganate La0.5Ca0.5MnO3

A huge positive magnetovolume effect is shown for the first time as the cha rge order in La0.5Ca0.5MnO3 is destroyed under an applied magnetic field. T he sign of this effect is opposite to the one expected from the study of th e charge ordered Pr0.7Ca0.3MnO3 compound. These results strongly support th at a structural transition from the low volume (charge ordered antiferromag netic monoclinic) to the high volume (ferromagnetic metallic orthorhombic) phase is induced by the magnetic field application. Only the closeness of t he free energies of these phases can explain that the charge ordering can b e collapsed by a low Zeeman energy. (C) 1999 Elsevier Science Ltd. All righ ts reserved.