Interplay of charge and spin ordering in Pr0.65Ca0.35-xSrxMnO3
| Autor: | Hui-Long Huang, 黃慧龍 |
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| Rok vydání: | 2002 |
| Druh dokumentu: | 學位論文 ; thesis |
| Popis: | 90 The manganites of the type RMnO3 (R=La, Nd, Pr, Sm) are antiferromagnetic and the end (n= µ) members of the so-called Ruddlesden-Popper series, Rn+1MnnO3n+1. These oxide materials illustrate many interesting properties like colossal magnetoresistance (CMR)1-13, charge ordering (CO)14-21, magnetic field induced structural and ferromagnetic transitions22-24 when R is partially substituted by divalent cation A (=Ca, Sr, Ba, Pb) as R1-xAxMnO3. According our results of resistivity (r) and specific heat (C) on the Pr1-xCaxMnO3 series, we confirmed the Pr0.65Ca0.35MnO3 is the good choice to investigate the interplay of double exchange (DE) interaction and charge(CO)/orbital(OO) ordering. A systematic study of r, magnetization (M) and C on polycrystalline Pr0.65Ca0.35-xSrxMnO3 (x=0-0.35) perovskite manganites has been reported. The T-x phase diagram presenting their electrical and magnetic properties is prevailed. The Pr0.65Ca0.25Sr0.1MnO3 (for x=0.1) sample is particularly unique showing a CO transition at TCO ~ 200K, an antiferromagnetic (AFM) ordering transition at TN ~ 175K, a metal-insulator (MI) transition at TMI ~ 80K and a ferromagnetic (FM) ordering transition at TC ~ 45K in the absence of magnetic fields. However, the C data of it do not show any anomaly at TMI for MI transition but illustrates a much smaller anomaly than expected one at TC and is suppressed by magnetic fields. This may indicate that the FM ordering in it, commonly related to MI transition, is of meta-stable characteristic and is ascribed to electronic and magnetic instability induced by spin fluctuations. This is established from the T-H phase diagram, as well as the thermal and magnetic hysteresis in r, M and C. |
| Databáze: | Networked Digital Library of Theses & Dissertations |
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