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A chemical method with small polymer templates of polyvinyl alcohol is explored to obtain nanoplates (15-35 nm thickness) of La0.67Ca0.33MnO3 of single magnetic domains. X-ray diffraction reveals a single phase La 0.67Ca 0.33MnO 3 of an orthorhombic crystal structure after heating the precursor at 600-1000degC for 2 h in air. At low temperature 10 K, as large coercivity Hc as 411 Oe has been found in nanoplates processed at 600degC. As per a reasonably small value Ms = 30.7 emu/g for the saturation magnetization, in a spin exchange coupled system, the magnetic spins in the shell order opposite to those in the core. The shell serves as a pinning barrier to support such high Hc -value. First derivative of the thermomagnetic curve reveals a broad peak at ~ 254 K in the T C point. Upon raising the processing temperature to 800 or 1000degC, the Ms improved markedly to 86.7 or 91.1 emu/g but the Hc-value decreased to 143 or 36 Oe. A sharp T C point occurs around 268 K with a spin flipping near 40 K. Results are discussed in correlation to the observed microstructures.
Date of Publication: Oct. 2009