Abstract
Abstract We present a comparative study of the effect of divalent doping on structural, magnetic and magneto-transport properties of ( La 0.4 Pr 0.6 ) 1 - x Ca x MnO 3 (x = 3/8, 1/3) mixed phase manganites. Structural analysis, using X-ray and neutron diffraction studies, reveals a similar orthorhombic crystal structure with Pnma space group for both the samples; however, x = 3/8 composition shows higher octahedral distortion. The temperature dependent resistivity shows signature of a first order metal-insulator transition with conduction through percolative paths for both the samples. A broad thermal hysteresis observed in temperature dependent magnetization as well as magneto-transport data indicates coexistence of different magnetic phases like metallic ferromagnet, and insulating charge ordered antiferromagnetic in both the manganites. The variation of magnetization profiles with temperature for these stoichiometrically similar compositions is found to be remarkably different, with the dominance of charge ordered-antiferromagnetic phase in the x = 3/8 composition and ferromagnetism in the x = 1/3 composition. The field dependent magnetization isotherms show significantly higher fraction (≈2 times) of ferromagnetic phase in x = 1/3 composition as compared to x = 3/8 composition. The metal-insulator transition temperature is also found to be higher for composition with x = 1/3 (155 K) than that for x = 3/8 (112 K). In an applied magnetic field of 8 T, the resistivity changes drastically as the charge order melts and gives way to stable ferromagnetic metallic behaviour with higher metal-to-insulator transition temperature. The temperature dependent magnetoresistance shows a significant variation for the samples, with maximum value of around 3 × 10 5 % and 7 × 10 4 % for x = 3/8 and x = 1/3 compositions, respectively. These observations suggest that inspite of a very small variation in divalent doping, the magnetic phase fractions in these two manganites are significantly different.
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