Hamburg 2001 – scientific programme

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AM: Magnetismus

AM 3: Magnetowiderstand I

AM 3.14: Talk

Monday, March 26, 2001, 17:45–18:00, S 5.2

Effect of Spin Polarized Tunneling in Transport properties of CMR Manganites — •Chiranjib Mitra^1,2, Kathrin Dörr², and Karl-Hartmut Müller² — ¹TIFR , Homi Bhabha Road, Colaba, Mumbai 400 005, India — ²IFW Dresden, Postfach 270116, 01171 Dresden, Germany

La_0.7Ca_0.3MnO₃ and La_0.7Sr_0.3MnO₃ are perovskites manganites exhibiting colossal magnetoresistance (CMR) at the ferromagnetic ordering temperature, where upon application of large magnetic fields (∼ Tesla) the spin disorder resistivity is suppressed giving rise to an enormous MR near T_C. These systems behave as half metallic ferromagnets and this produces a low field MR below T_C in polycrystalline films and granular materials owing to the spin polarized tunneling (SPT) of the heavily polarized conduction electrons across the grain boundaries which act as insulating barriers. In this work we have investigated the effect of SPT across artificially fabricated tunnel junction in CMR-Insulator-CMR multilayers. From our current perpendicular to plane (CPP) transport data we have observed a very intriguing temperature dependence of MR, which is attributed to arising from the temperature dependent evolution of density of states (DOS) in manganites below T_C owing to the large Hund’s coupling. We also observe a gradual suppression of Jahn-Teller polarons with decrease in temperature below T_C in our tunneling resistance data.