Open atmosphere synthesis and wide range colossal magnetoresistance in La_(0.7)Sr_(0.3-x)Hg_x MnO_3 (0≤x≤0.2) system

摘要

We have synthesized several polycrystalline samples with nominal compositions La_(0.7)Sr_(0.3-x)Hg_xMnO_(3+δ)(0≤x≤0.2) by the standard solid-state reaction method. Instead of the sealed quartz tube method widely employed for the Hg-based systems, we adopted open atmosphere synthesis route. All the samples exhibited monophasic nature with rhombohedral structure as revealed by the X-ray diffraction data. A variation in the unit cell volume is observed with x, which is interpreted as a result of extra oxygen in-diffusion and subsequent cation vacancy creation. A broad metallic behavior is seen in the entire temperature range from 300 to 4 K. The samples showed varying amount of colossal magnetoresistance depending upon the temperature and applied magnetic field. The MR value as high as 30% was observed in x = 0.2 sample and the MR is persistent over a wide temperature range with a little change in magnitude.