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- 저자 : T. R. N. Kutty (검색결과 1 건)
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T. R. N. Kutty,John Philip 한국물리학회 2002 Current Applied Physics Vol.2 No.3
La0:667Ca0:333Mn 1. xM xO3. d (M ¼ Mg, Li or Re) exhibit insulating behaviour and nonlinear currentvoltage (JE) relationshipwith voltage-limiting characteristics at temperatures below the ferromagnetic transition (Tc). The high current region is set in at eldstrengths< 60 V/cm. Nonlinearity exponent,a in the relationJ¼ kEa increases inversely with temperature. In presence of an externalmagnetic eld, theJE curves show higher current density at lower eld strengths. Microstructural studies indicate that there is nosegregation of secondary phases in the grain boundary regions. There is remarkable changes inqðTÞas well asJE curves with thegrain size. Annealing studies in lowerpO2 atmospheres indicate that there is signicant out-diusion of oxygen ions through the grainboundary layer (GBL) regions creating oxygen vacancies in the GBL regions. The concentration of Mn4þ ions is lowered at the GBLintroduced between two conducting grains and the carrier motion between the grains is inhibited. Thus belowTc, where sucientincrease in resistivity is observed the conduction may be arising as a result of spin dependent tunneling across the barrier. Externalelectric eld lowers the barrier height and establishes carrier transport across the barrier. Above certain eld strength, barrier heightdiminishes signicantly and thereby allowing large number of carriers for conduction, giving rise to highly nonlinear conductivity.. 2002 Elsevier Science B.V. All rights reserved.
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