Effect of isovalent doping of manganite (La1-xPrx)0.7Ca0.3MnO3 films (0 ≤ x ≤ 1) on their optical, magnetooptical, and transport properties near the metal-insulator transition

The optical, magnetooptical, and electric properties of epitaxial (La1 - xPrx)(0.7)Ca0.3MnO3 films (0 less than or equal to x less than or equal to 1) grown by MOCVD on LaAlO3 and SrTiO3 substrates were studied. It is shown that the decrease in the average cation radius resulting from isovalent substitution of the Pr for La ions brings about a lowering of the Curie temperature, the metal-insulator transition temperature, and the temperatures of the maxima in magnetotransmission (MT) and magnetoresistance (MR). These temperatures depend only weakly on the substrate type. Substitution of La by Pr does not change the shape of the spectral response of the transverse Kerr effect. For concentrations x less than or equal to 0.50, the maximum values of the Kerr effect and of the MT vary insignificantly, which should be assigned to the existence of a singly connected ferromagnetic metallic region at low temperatures. In films with x = 0.75, the presence of ferromagnetic metallic drops in an antiferromagnetic insulating matrix was revealed. The totality of the experimental data obtained suggest that nanoscopic magnetic and electronic nonuniformities exist both in films with a singly connected metallic region and in an x = 1 film, which is an antiferromagnetic insulator. (C) 2004 MAIK "Nauka / Interperiodica".