Changes in the electronic, optical, and magnetic properties of LaSrMnO films upon transition from the rhombohedral phase to the orthorhombic phase

The properties of LaSrMnO films are investigated in the temperature range of the transition from the rhombohedral phase to the orthorhombic phase (600-650degreesC). It is shown that, with a variation in the growth temperature T-s, the change in the film properties is governed by the interaction of Mn-O metallic (ferromagnetic) clusters in the dielectric (antiferromagnetic) matrix. At T-s less than or equal to 600degreesC, the low density of e(g) states and the dielectric gap (E-g = 0.3-0.5 eV) are responsible for the following features: (i) the optical transparency in the range homega = 0.5-2 eV, (ii) the difference between the FC and ZFC magnetizations M(T), (iii) the high resistance, and (iv) the appearance of the portions R(T) approximate to const in the dependence R(T) due to the transformation of clusters into a system of tunnel-coupled quantum dots. At T-s greater than or equal to 650degreesC, the local increase in the atomic and electronic densities leads to a decrease in the optical transmission and the resistance by three to nine orders of magnitude, the appearance of a maximum and a minimum in the dependences R(T) of the LaSrMnO films, and an increase in the magnetization M(10 K) by one order of magnitude. The inference is drawn that magnetic ordering of the system of tunnel-coupled clusters encourages an increase in the cluster size and in the content of the metallic (ferromagnetic) phase. (C) 2004 MAIK "Nauka / Interperiodica".