Synthesis, Characterization, and Electromagnetic Wave Absorbing Properties of La0.7Sr0.3MnO3

Perovskite manganese La_0.7Sr_0.3MnO₃ (LSMO) powders were prepared by sol-gel synthesis and calcination in the temperature (T) range of 500~1200 o C and their structures and electromagnetic (EM) wave absorption properties were investigated. X-ray diffraction (XRD) analysis revealed that the crystalline perovskite phase can be formed at T ≥ 600 ^oC. The average grain size was ~15 nm at the calcination temperature (T_cal) = 600 ^oC and it increased to ~1 μm when T cal increased up to 1200 ^oC. M-H curves of the samples showed soft magnetic behaviors for all the crystallized samples, and the value of saturation magnetization increased with increasing T_cal. The real and imaginary parts of permittivities and permeabilities were measured on LSMO powder-epoxy (10 wt%) composites using a network vector analyzer in the frequency range of 100 MHz ≤ f ≤ 18GHz. The complex permittivities (ε', ε") increased significantly in samples calcined above 800 ^oC because the concentration of free electrons increased, due to the LSMO's unique magnetotransport effect, as the crystallinity and the M_S value increased significantly. As the T_cal increased, the height of the μ' and μ" spectra also gradually increased. The large values of ε', ε" of the LSMO-epoxy are dominant factors in the EM wave absorption characteristics, and it showed good absorption characteristics when it had a thickness of 1.5 mm or less at a frequency of 12 GHz or higher. At the same time, it also exhibited EM wave shielding ability by reflection in the several GHz band.