AVS 45th International Symposium
    Magnetic Interfaces and Nanostructures Technical Group Tuesday Sessions
       Session MI-TuA

Paper MI-TuA4
Unusual Magnetic Ordering at Room Temperature in La-Ca-Mn-O Thin Films

Tuesday, November 3, 1998, 3:00 pm, Room 324/325

Session: Emerging Materials and Hybrid Structures
Presenter: S.E. Lofland, University of Maryland
Authors: S.E. Lofland, University of Maryland
V.V. Srinivasu, University of Maryland
S.M. Bhagat, University of Maryland
R. Shreekala, University of Maryland
M. Rajeswari, University of Maryland
T. Venkatesan, University of Maryland
Correspondent: Click to Email
Epitaxial thin films with a nominal composition of La@sub 0.8@Ca@sub 0.2@MnO@sub 3@ were grown by pulsed-laser deposition with thicknesses ranging between 300 and 2600 Å. The resistivity of the as-grown films had a peak near 210 K, similar to the value found in the bulk material. Electron spin resonance studies showed the films to be magnetically very inhomogeneous with no indication of ordering above 240 K. Subsequent heat treatment of the films at 900° C for an hour in flowing oxygen led to dramatic property changes. The resistvity peak temperature increased significantly, and in most cases was above 300 K while the magnitude of the resistivity was markedly less. Resonance experiments suggested that treated films less than 1000 Å thick were paramagnetic at room temperature; however, films thicker than 1000 Å showed multiline spectra at 300 K, with at least one line resulting from a ferromagnetic spin system. In the thickest film, resonance data suggested that 10% of the film was ferromagnetic at room temperature. This is in contradiction to the accepted phase diagram ordering temperature of around 220 K and the maximum ordering temperature of 270 K for the La@sub 1-x@Ca@sub x@MnO@sub 3@ system. We discuss how these observations may be reconciled. Supported in part by the National Science Foundation under Grant No. DMR-9632521.