Nonlinear electrical response in a non-charge-ordered manganite:Pr0.8Ca0.2MnO

Abstract

Up to now, electric field induced non-linear conduction in the Pr 1−x Ca x MnO 3 system has been ascribed to a current-induced destabilization of the charge ordered phase. However, for x ≤ 0.25, a ferromagnetic insulator state is observed and charge-ordering is absent whatever the temperature. A systematic investigation of the non-linear transport in the ferromagnetic insulator Pr 0.8 Ca 0.2 MnO 3 shows rather similar results to those obtained in charge ordered systems. However, the experimental features observed in Pr 0.8 Ca 0.2 MnO 3 are distinct in that the collapse of the CO energy gap can not be invoked as usually done in the other members of the PCMO system. We propose interpretations in which the effectiveness of the DE is restored upon application of electric field.Typeset using REVT E X 1 Hole-doped perovskite manganese oxides R 1−x AE x MnO 3 (R and AE, being trivalent rare-earth and divalent ions, respectively) are associated with a wide variety of electronic and magnetic properties depending on the value of x and the averaged A-site cation radius, r A .1 These materials have recently been the subject of intense studies due to intriguing phenomena such as charge/orbital ordering (CO) 2 or colossal magnetoresistance (CMR). 3The latter is usually interpreted by means of the double-exchange interaction (DE) scenario 4 which gives an interesting qualitative interpretation of coupled ferromagnetic ordering and metallicity. Within such a framework, the ferromagnetic (FM) ordering is related to a large electronic itinerancy i.e. metallic behavior. Among the various mixed valent manganites studied so far, the Pr 1−x Ca x MnO 3 system (PCMO) is perhaps the most interesting because it shows a great variety of ordered phases very sensitive to cation / anion doping. This produces a decrease of the magnitude of the e g bandwidth and,consequently, in a reduction in the effectiveness of the double exchange. On the other hand, for x ≤ 0.25 we deal with a very low hole concentration which does not favor a delocalized electronic state.The aim of our experience was to investigate whether a current-induced metal-insulator transition can be observed in a non-CO manganite of the PCMO system. For this purpose, a crystal of Pr 0.8 Ca 0.2 MnO 3 , not so far from the CO region, has been chosen. Although a M-I transition has not been clearly observed, the resistance for increasing bias current is drastically reduced. Moreover, strong non-linear electrical conduction is found with a NDR developing for T < T c . This behavior is not sensitive upon application of a magnetic field.Compared to already reported results, the experimental features observed here are distinct in that the collapse of the CO energy gap can not be invoke as usually done in the other members of the PCMO system. 17,18,[20][21][22][23][24][25] Using the floating-zone method with a feeding rod of nominal composition Pr 0.8 Ca 0.2 MnO 3 , a several-cm-long single crystal was grown in a mirror furnace. Two samples were cut out of the central part of this ...

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“…[7][8][9] Nonlinear conductivity was also observed in charge ordered manganite perovskites, and may be linked to the melting of charge order and creation of conducting filaments above a certain threshold current. [10][11][12] This is qualitatively different to our findings where the nonlinear conduction occurs predominantly at low currents and appears to be intrinsically linked to the ferromagnetic ordering.…”

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“…Thus they have invoked a growing of FM-volumic-clusters along the direction of injected-current that would be at the origin of such a percolation-based scenario. A more recent paper 20 has also shown the presence of the same non-linearity in a non-charge-ordered composition (x=0.2) in which the percolation model was not applicable adding complexity to this features.…”

Colossal electroresistance without colossal magnetoresistance in La0.9Sr0.1MnO3

“…Different interpretations for these nonlinearities included depinning of CO state, 3 depinning of charge density waves, 4 or change in the orientation of orbital ordering ͑OO͒. 5,6 Indeed, nonlinear effects were subsequently found in materials without CO,7,8 undermining the interpretation of "melting" of CO/OO states.Recent reports tend to interpret the nonlinear I-V characteristics in manganites as the consequence of Joule heating due to large currents. [9][10][11] In the case of resistive curves with a maximum in R͑T͒, current localization on conductive paths and self-heating was suggested to explain the concomitant increase and decrease of resistance with increasing current.…”

“…Different interpretations for these nonlinearities included depinning of CO state, 3 depinning of charge density waves, 4 or change in the orientation of orbital ordering ͑OO͒. 5,6 Indeed, nonlinear effects were subsequently found in materials without CO, 7,8 undermining the interpretation of "melting" of CO/OO states.…”