We performed a comparative study on the colossal negative magnetoresistivity and the Hall effect in thin films of the manganese perovskite La 1-x Ca x MnO 3 with x =0.3 and x =0.67. The underdoped sample ( x =0.3) undergoes a phase transition from a paramagnetic semiconductor to a ferromagnetic quasimetal at the Curie temperature T C =280 K , while the overdoped compound ( x =0.67) stays a paramagnetic semiconductor at all temperatures. Both materials show colossal negative magneto-resistivity, albeit on considerably different temperature- and field scales, depending on the magnetic interactions between neighbouring Mn ions. According to the Hall data, the charge carriers in the underdoped material are hole-type, partially compensated by an electron-type contribution. The overdoped system shows electronic carriers with a thermally activated concentration. The ordinary Hall effect is in both compounds superimposed by an anomalous Hall contribution with a sign opposite to the intrinsic charge-carrier type.
Exploring the intrinsic limit of the charge-carrier-induced increase of the Curie temperature of Lu- and La-doped EuO thin films