Layered microdomains and columnar grains in epitaxial La 0.7 Ca 0.3 MnO 3 films and Y 0.7 Ca 0.3 MnO 3 /La 0.7 Ca 0.3 Mn
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G.C. Xiong and G.J. Lian National Mesocopic Physics State Key Laboratory and Department of Physics, Peking University, 100871 Beijing, People’s Republic of China (Received 2 February 2000; accepted 9 August 2000)
Epitaxial La0.7Ca0.3MnO3 thin film and [Y0.7Ca0.3MnO3/La0.7Ca0.3MnO3]10 multilayers of about 140 nm in thickness were grown by pulsed laser deposition on (001)LaAlO3. Their microstructures were investigated by transmission electron microscopy and associated techniques. It was found that both the film and the multilayers contain an almost defect-free layer near the substrate, followed by columnar grain grown. The columns were separated by strained regions in the top layer. No interfacial dislocations were observed at either of the La0.7Ca0.3MnO3/LaAlO3 or the Y0.7Ca0.3MnO3/ La0.7Ca0.3MnO3 interfaces. Interestingly, both the epitaxial film and the multilayers exhibited layered crystallographic domains. The formation mechanisms of the layered domain structures observed are discussed.
I. INTRODUCTION
Recently, the observation of large magnetoresistance (MR) effects at room temperature in epitaxial Ln1−xAxMnO3 (Ln ⳱ lathanides, A ⳱ alkaline earth elements or Pb) thin films has renewed interest in the doped manganite perovskite materials for potential magnetic random access memory and read-head applications.1–4 However, a high magnetic field (several tesla) required for large MR still remains a barrier for any significant practical applications. Various efforts have been made to improve the low-field MR response of manganites. Such works include trilayer tunnel junctions,5–7 polycrystalline thin films,8–11 orthogonal grain chains,12 artificially induced grain boundaries,13,14 specially designed structures to focus the magnetic field,15 etc. And it seems that introducing weak-link grain boundaries and interfaces is a promising way to enhance the low-field MR response in manganite films. It has been shown that, in bulk materials, the Curie temperature Tc and MR in high magnetic fields are extremely sensitive to chemical pressure and hydrostatic pressure.16,17 Several groups have reported that lattice strain affects the peak resistance temperature Tp and MR
a)
Also at the Department of Physics, Hubei University, Wuhan 430062, People’s Republic of China. b) Also at the School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0245. 2454
http://journals.cambridge.org
J. Mater. Res., Vol. 15, No. 11, Nov 2000 Downloaded: 18 Mar 2015
properties of La0.7Sr0.3MnO3 (LSMO),18 La0.7Ca0.3MnO3 (LCMO),19 and La0.8Ca0.2MnO3,20 thin films, and the strain-induced magnetoelastic interaction plays a dominant role in the magnetic anisotropy.18,4,21 Wang et al.22 reported that large low-field MR had been obtained in compressively strained Pr0.67Sr0.33MnO3 (PSMO) ultrathin (
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