Chemical disorder effects in transport and magnetic properties of perovskite manganite
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Sandip Chatterjeea) Tata Institute of Fundamental Research, Mumbai, 400005, India
P. Chatterjee Department of Physics, Vivekananda Mahavidyalaya, Hoogly 712405, West Bengal, India
A.K. Nigam Tata Institute of Fundamental Research, Mumbai 400005, India
S.K. De Department of Materials Science, Indian Association for the Cultivation of Science, Calcutta 700 032, India (Received 22 July 2004; accepted 28 October 2004)
The dependence of the novel properties observed in colossal magnetoresistance (CMR) materials, other than average ionic radii 〈rA〉 and Mn valence ratio (Mn3+/Mn4+), was investigated through examination of the transport and magnetic properties of Pr0.65(Ca0.7Sr0.3)0.35MnO3, La0.123Pr0.527(Ca0.8Sr0.2)0.35MnO3, and Pr0.65(Ca0.866Ba0.134)0.35MnO3. The average ionic radii 〈rA〉 and valence ratio of all three samples have been kept equal. The results of this investigation indicate a more intense role of the nature of individual A-site cation and the lattice mismatch. A remarkably large magnetoresistance of the order of 108 at moderate magnetic field has been observed for Ba-doped sample. I. INTRODUCTION
In recent years, rare-earth manganites have been extensively studied not only for their colossal magnetoresistance property but also for the novel and rich electrical and magnetic phases.1–3 In the rare-earth manganite systems, the charge ordering (CO) antiferromagnetic phase is as important as the ferromagnetic one since melting of the CO state by applied magnetic field can produce large colossal magnetoresistance.4 In the case of low bandwidth manganites (Pr1−xCaxMnO3), for a broad range of doping (0.3 艋 x 艋 0.75) an antiferromagnetic charge ordered state is stabilized.5 Whereas for large bandwidth compound (e.g., La1−xSrxMnO3) no CO is observed, for intermediate bandwidth compound (e.g., La1−xCaxMnO3), CO is stabilized to a certain range of doping. 6,7 Interestingly, the CO state of Pr0.65Ca0.35MnO3 can be destroyed by application of magnetic field.8 Also, when Sr is doped in the Ca site of Pr0.65Ca0.35MnO3, the metal–insulator (M-I) transition appears, and as doping of Sr increases to 50%, CO
a)
Present address: Department of Physics, Government College of Engineering and Textile Technology, Serampore 712201, WestBengal, India. DOI: 10.1557/JMR.2005.0114 J. Mater. Res., Vol. 20, No. 4, Apr 2005
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completely disappears.9,10 This is due to the fact that with Sr doping, average ionic radii 〈rA〉 increases and eg bandwidth increases. Therefore, the M-I transition appears, and CO disappears. Moreover, as 〈rA〉 decreases, the tolerance factor also decreases, which directly induces the reduction of the Mn–O–Mn bond angle from 180°. The hopping amplitude for carriers to move from Mn to Mn naturally decreases as becomes smaller than 180°.11As a matter of fact, in low bandwidth compounds, the carriers become localized. Therefore, 〈rA〉 is a crucial factor in the charge ordering properties of perovskite manganite. Furthermore, most of the low and intermediate
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