Grain size dependent magnetization, electrical resistivity and magnetoresistance in mechanically milled La 0.67Sr 0.33MnO 3

Abstract

We have studied magnetization, ac susceptibility, resistivity and magnetoresistance in mechanically milled La 0.67Sr 0.33MnO 3. The material with grain size micron to nanometer scale has stabilized in rhombohedral crystal structure with space group R3 C. We have found various grain size effects, e.g., decrease of ferromagnetic moment, increase of surface spin disorder, and appearance of insulator/semiconductor type resistivity. In addition to these conventional features, we have identified a magnetic anomaly at 45 K in bulk sample. Ferromagnetic to paramagnetic transition temperature ( T C) is above room temperature for all samples. The samples are typical soft ferromagnet that transformed from multi-domain state to single domain state in nanocrystalline samples. The remarkable observation is that low temperature freezing of ferromagnetic domains/clusters does not follow the conventional spin glass features. Experimental results clearly showed the enhancement of high field magnetoresistance in nanocrystalline samples below 200 K, whereas low field magnetoresistance gradually decreases above 200 K and almost absent at 300 K. We have discussed few more magnetic and electrical changes, highly relevant to the progress of nanomaterial research in ferromagnetic manganites.