DC electrical current-dependent resistance and pulsed current-voltage characteristics as a function of temperature of mixed valent Mn oxide-based La5/8-yPryCa0.375MnO3 (y = 0.35) single crystals are reported. We find that the low-temperature regime of this material is strongly current dependent. For small current densities (∼ 10μA/cm2), the metal-insulator transition related to the low-temperature enlargement of the ferromagnetic fraction is not observed down to 10K. Higher current densities causes a large decrease of the resistance, which is temperature dependent and exhibits memory effects. Our results are interpreted within a scenario of strong competition between charge and ferromagnetic ordering. © 2004 Published by Elsevier B.V.Fil: Garbarino, Gaston Leonel. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Monteverde, Martin. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigación y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Bariloche). División Bajas Temperaturas; ArgentinaFil: Acha, Carlos Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; ArgentinaFil: Levy, Pablo Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; ArgentinaFil: Quintero, M.. Comisión Nacional de Energía Atómica; ArgentinaFil: Koo, T.Y.. Rutgers, The State University Of New Jersey; Estados UnidosFil: Cheong, S.-W.. Rutgers, The State University Of New Jersey; Estados Unido

Acha, Carlos Enrique

Cheong, S.-W.

Garbarino, Gaston Leonel

Koo, T.Y.

Levy, Pablo Eduardo

Monteverde, Martin

Quintero, M.

Physica B Condensed Matter

LAReferencia - Red Federada de Repositorios Institucionales de Publicaciones Científicas Latinoamericanas

ARTICLE IN PRESS0921-4526/$ - sedoi:10.1016/j.phCorrespondiE-mail addre1Also at CRT2Also fellow3Also fellowPhysica B 354 (2004) 16–19www.elsevier.com/locate/physbCurrent-induced effects in La5=8yPryCa3=8MnO3 ðy ¼ 0:35Þsingle crystalsG. Garbarinoa, M. Monteverdea,1, C. Achaa,,2, P. Levyb,3, M. Quinterob,T.Y. Kooc, S.-W. CheongcaLaboratorio de Bajas Temperaturas, Departamento de Fı́sica, FCEyN, Universidad de Buenos Aires, Ciudad Universitaria,(C1428EHA) Buenos Aires, ArgentinabDepartamento de Fı́sica, Comisión Nacional de Energı́a Atómica, Gral Paz 1499, 1650 San Martı́n, Buenos Aires, ArgentinacDepartment of Physics and Astronomy, Rutgers University, NJ, USAAbstractDC electrical current-dependent resistance and pulsed current–voltage characteristics as a function of temperature ofmixed valent Mn oxide-based La5=8yPryCa0:375MnO3 ðy ¼ 0:35Þ single crystals are reported. We find that the low-temperature regime of this material is strongly current dependent. For small current densities ( 10mA=cm2Þ; themetal–insulator transition related to the low-temperature enlargement of the ferromagnetic fraction is not observeddown to 10K. Higher current densities causes a large decrease of the resistance, which is temperature dependent andexhibits memory effects. Our results are interpreted within a scenario of strong competition between charge andferromagnetic ordering.r 2004 Published by Elsevier B.V.PACS: 71.30.þh; 72.15.Eb; 72.20.Ht; 75.47.LxKeywords: Non-linear effects; Manganites; Percolation; Phase separation1. IntroductionThe magnetic phase separation scenario thatpresents some manganites can be very useful toe front matter r 2004 Published by Elsevier B.V.ysb.2004.09.011ng author. Fax: +05411 45763357.ss: acha@df.uba.ar (C. Acha).BT (CNRS) Grenoble, France.of CONICET of Argentina.of CONICET of Argentina.produce samples with a controlled mixtureof charge-delocalized ferromagnetic (CD-F)and charge-ordered, antiferromagnetic (CO-AF)phases. It will be technically interesting to ex-ternally control the proportions of these highlyconducting and insulating mixtures as a change inthe resistivity of several orders of magnitude canbe obtained as a consequence of the percolatingnature of the problem [1]. This kind of frameworkwas already observed for hole-doped manganitesARTICLE IN PRESSG. Garbarino et al. / Physica B 354 (2004) 16–19 17[2–4], particularly for the ðLa;Pr;CaÞMnO3 com-pound [5,6], where the conducting phase can betuned by temperature, magnetic or electric field,time or grain size. Indeed, it was previously shownthat this prototypical manganite is magneticallyphase separated into the mixture already men-tioned, as a consequence of the intricate interplaybetween metallic F and the AF interactions [1]. Inthis paper we present measurements of theelectrical field dependence (DC and pulsed) ofthe resistance as a function of temperature inLa5=8yPryCa3=8MnO3 ðy ¼ 0:35Þ single crystals.Our results can be interpreted within a percolationscenario where the proportion of the CD-F phaseover the CO-AF is favored by the application ofan electric field.2. ExperimentalSingle crystals of nominal compositionLa5=8yPryCa3=8MnO3 (LPCMO, y ¼ 0:35) weresynthesized and characterized as was describedpreviously [7]. The resistivity was measured as afunction of temperature ð4KpTp300KÞ andelectric field, following different configurations: afour terminal (4W) standard configuration forconstant current measurements and a two wire(2W) configuration for high resistivities (up to100GO—using a Keithley 2400 SourceMeter) orfor a constant voltage measurement. Pulsedmeasurements were performed, depending on themagnitude of their period, by generating a singlesquare pulse of increasing voltages (up to 10V) for20ms to 2 s (Agilent 33250A 80MHz Function/Arbitrary Waveform Generator) and determiningthe current by measuring the voltage in acalibrated resistance using an oscilloscope ordirectly with the SourceMeter for longer pulses.Temperature was measured by a small diodethermometer thermally anchored directly to thesample.Fig. 1. Resistivity (2W, voltage controlled) of LPCMO as afunction of temperature for various applied voltages. Thetemperature evolution is indicated by arrows. The inset showsthe 4W, current controlled resistivity.3. Results and discussionThe resistivity of a LPCMO ðy ¼ 0:35Þ singlecrystal as a function of temperature for differentconstant voltages is displayed in Fig. 1. For smallvoltages (Vp10VÞ; the sample remains insulatingdown to low temperatures. When higher voltagesare applied ð10VpVp100VÞ; a metal–insulator-like transition can be observed, reaching morethan four orders of magnitude of resistivity dropfor the highest voltages. Characteristic tempera-ture hysteresis of this system can also be observed.The voltage dependence of the resistivity (rðV Þ), ata fixed temperature for a sample cooled in zeroapplied voltage, is shown in Fig. 2. When voltageis increased, we measured a very high resistance(HR) that remains nearly constant until a tem-perature-dependent critical voltage (V c) isreached, where a drop of more than four ordersof magnitude is observed. In these conditions, atime evolution of the resistivity can also beobserved, a reduction of the resistivity can benoticed even for a constant applied voltage. Whenthe voltage is decreased, the sample shows memoryeffects, remaining in a different and more con-ducting low resistance—regime (LR). If thevoltage is increased again, a nonlinear dependenceis observed, even for voltages lower than V c:Considering that the decrease of the resistanceproduces an increase of the Joule dissipation in thesample, the highest voltage parts of these rðV Þcurves could be modified by overheating. To ruleout this possibility, we performed pulsed RðV ÞARTICLE IN PRESSFig. 2. Resistivity of LPCMO as a function of the appliedvoltage at T ¼ 15K and T ¼ 19K: The system evolves from aHR to a LR regime, after applying a voltage VXV c:5 915 9107106ρ (MΩ cm)V (V)τ = 20ms τ = 200msτ =  2sV (V) ρ (Ω cm)τ = 20msDCT = 7K0.3377Fig. 3. Resistivity of LPCMO as a function of voltagemeasured applying single square pulses of t ¼ 20ms comparedto DC measurements. The inset shows the comparison of theRðV Þ curves obtained with t ¼ 20ms; 200ms, and 2 s.Fig. 4. Time evolution of the resistivity and of the calculatedCD-F volume fraction f ðtÞ (Eq. (1)) after applying a voltageVXV c at T ¼ 13K:G. Garbarino et al. / Physica B 354 (2004) 16–1918measurements in the LR regime. As can beobserved in Fig. 3, no time dependence can beobserved for pulsed and DC voltages Vo10V:These results can be analyzed considering thegeneral effective medium (GEM) equations devel-oped by Mclachlan [8] to describe the electric orthermal conductivity of a binary mixture ofconducting and insulator materialsfðs1=tM  s1=tE Þðs1=tM þ As1=tE Þþ ð1 f Þðs1=tI  s1=tE Þðs1=tI þ As1=tE Þ¼ 0; (1)where f is the volume fraction of the CDFdomains, sM and sI the conductivities of themetallic and insulating phases, respectively. sE isthe effective conductivity that we measure, t acritical exponent, and A ¼ ð1 f c=f cÞ; where f c isthe percolation threshold.Assuming a 3D percolation scenario ðt ¼ 2; f c ¼0:17Þ and that sMðTÞ ¼ sðTÞ of x ¼ 0 and sIðTÞ ¼sðTÞ of x ¼ 0:625; the f ðV Þ and f ðtÞ values can beobtained, fitting our data with the GEM equation.The obtained f ðtÞ and f ðV Þ dependencies areshown in Figs. 4 and 5, respectively. In somecases, not shown here, we obtained that f ðtÞ;f ðV Þ40:17; with a corresponding metallic-liketemperature-dependent resistivity for temperaturesin the 10KoTo20K range.The nonlinearities observed in the LR regime(I  aV þ bV 7=3 þ cV 7=2; as shown in Fig. 6)indicate the presence of a different conductingmechanism, which can be associated with tunnel-ing processes [9] described, particularly, by theGlazman–Matveev (GM) theory [10]. Thus, theseresults point out a rich scenario where the voltagedependence of the resistivity of LPCMO singlecrystals can be related to different processes: aclassical percolating framework in a conductin-g–insulating phase mixture and, when the condi-tions are favorable, tunneling processes betweenconducting paths separated by small insulatingbarriers.ARTICLE IN PRESSFig. 5. Voltage sensitivity of the resistivity and of the CD-Fvolume fraction (f ðV Þ) in the LR regime at T ¼ 13K: Thedashed line indicates the critical value f c:T = 8.9KI =G0 * V + G1 * Vα + G2 Vβ α ≈ 2.3    β ≈ 3.510-510-710-90 1 2 3V (V)I (A)Fig. 6. Nonlinearities measured at T ’ 8:9K in the LR regime,which can be fitted (solid line) by the multi-step tunneling GMtheory.G. Garbarino et al. / Physica B 354 (2004) 16–19 194. ConclusionsWe have shown colossal electro-resistance ef-fects on LPCMO single crystals. Thus, we haveshown that the conductivity of the samples can bevaried with several orders of magnitude bysweeping an external voltage over a temperature-dependent critical value. Memory effects are thenobserved as a zero voltage low-resistivity meta-stable state is obtained. Our results can be ana-lyzed within the GEM formalism, indicating thatthe electronic properties of the LPCMO samplesare dominated by a percolative 3D conductionthrough the CD-F phase embedded in a CO-AFmatrix, while tunneling processes also seem to bepresent in the LR regime.AcknowledgementsPartial financial support from a CONICET PEIgrant is acknowledged. G.G., M.M. and M.Q.acknowledge a scholarship from CONICET ofArgentina and T.Y.K. and S.W.C. are supportedby the NSF-DMR-0103858. We are indebted toD. Giménez, D. Melgarejo and E. Pérez-Wodtkefor their technical assistance.References[1] M. Uehara, S. Mori, C.H. Chen, S.-W. Cheong, Nature(London) 399 (1999) 560.[2] A. Asamitsu, Y. Tomioka, H. Kuwahara, Y. Tokura,Nature (London) 388 (1997) 50.[3] P. Levy, F. Parisi, G. Polla, D. Vega, G. Leyva, H. Lanza,R.S. Freitas, L. Ghivelder, Phys. Rev. B 62 (2000) 6437.[4] V. Hardy, A. Wahl, C. Martin, Phys. Rev. B 64 (2001)064402.[5] N.A. Babushkina, A.N. Taldenkov, L.M. Belova, E.A.Chistotina, O.Y. Gorbenko, A.R. Kaul, K.I. Kugel, D.I.Khomskii, Phys. Rev. B 62 (2000) R6081.[6] N.K. Pandey, R.P.S.M. Lobo, R.C. Budhani, Phys. Rev. B67 (2003) 054413.[7] H.J. Lee, K.H. Kim, M.W. Kim, T.W. Noh, B.G. Kim,T.Y. Koo, S.-W. Cheong, Y.J. Wang, X. Wei, Phys. Rev.B 65 (2002) 115118.[8] D.S. McLachlan, J. Phys. C: Solid State Phys. 20 (1987)865.[9] S. Park, N. Hur, S. Guha, S.-W. Cheong, Phys. Rev. Lett.92 (2004) 167206.[10] L.I. Glazman, K.A. Matveev, Sov. Phys. JETP 67 (1988)1276.

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Current-induced effects in La5/8-yPryCa 3/8MnO3 (y = 0.35) single crystals

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Current-induced effects in La5/8-yPryCa 3/8MnO3 (y = 0.35) single crystals

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