| We report here the DC magnetic measurements of nano-crystalline perovskite systems La0.8Sr0.2FexMn1-xO3 (x = 0.02, 0.20), La1-yMn0.8Fe0.2O3 (y = 0.1, 0.2) in the temperature range 300K-20K. Samples synthesized by sol-gel technique show single-phase crystal structure with particle size 150-200Å ±20 Å. The magnetic moment increases initially with decrease in temperature showing a paramagnetic to ferromagnetic transition for all the samples. Further decrease in the temperature decreases the magnetic moment below 100K. The broad slope in FC curves could be attributed to nano particle size and with increase in Fe content the transition from Paramagnetic-Ferromagnetic-Antiferromagnetic becomes sharper. Mössbauer spectrums for all the samples show paramagnetic character at room temperature exhibiting a paramagnetic doublet. Mössbauer measurements at 80 K show magnetic ordering along with a central doublet for the Sr doped sample while there is no magnetic ordering seen for the vacancy doped samples. Occurrence of doublet in Mössbauer patterns at low temperature confirms the nanocrystalline nature of the samples indicating a superparamagnetic nature. Absence of metal-insulator transition and insulating nature observed in our temperature dependent resistivity studies in the temperature range 300-80K may be attributed to Fe doping and nanocrystalline nature of the samples. |
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