Grain size dependent magnetization, electrical resistivity and magnetoresistance in mechanically milled La0.67Sr0.33MnO3

Highlights: → Ferromagnetic nanoparticles of La0.67Sr0.33MnO3 have been synthesized by mechanical milling. → Detailed study of structure, magnetism and electrical properties has been discussed. → Low temperature magnetic anomaly has been identified in micron-sized bulk sample. → Low temperature resistivity minimum has been fitted with simple equation, considering the contribution of magnons. → Freezing of ferromagnetic domains below room temperature is non-conventional type and modified form of Vogel-Fulcher law is proposed. - Abstract: We have studied magnetization, ac susceptibility, resistivity and magnetoresistance in mechanically milled La0.67Sr0.33MnO3. The material with grain size micron to nanometer scale has stabilized in rhombohedral crystal structure with space group R3C. 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 (TC) 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.