Photonic crystals in biology - NanoTR-VI

PP andPPoster Session, Thursday, June 17Theme F686 - N11230BElectrical and Magnetic Properties of La0.67Ca0.33MnO3SrTiO 3 Nanocomposites111UShailendra Singh RajputUP P*, Leena JoshiP Sunita Keshri (Shaw)P1PDepartment of Applied Physics, Birla Institute of Technology, Mesra, Ranchi-835215, IndiaAbstractA composite series, has been studied in order to investigate the influence of STO phase onstructural and magneto transport properties of LCMO phase. By X ray diffraction and scanning electron microscopy we find that there is nointerdiffusion between the LCMO and STO phases. The EDX results show that the grains which are smaller in size and mainly distributed atthe grain boundaries and on the surfaces of LCMO grains are of STO phase. Measurements of resistivity on these samples reveal that parentsample shows a distinct metal insulator transition. The series exhibits a conduction threshold at , up to which extrinsictransition temperature decreases along with an increase in extrinsic magnetoresistance; whereas above these trends of variation arereversed. The magnetic phase transitions have been studied by the temperature variation of real () component of AC susceptibility as shownbelow. The parent LCMO sample undergoes a PM FM transition at . After addition of STO, remains almost same.Recently extensive research in nanotechnology andnanoscience is being carried out worldwide. Ananocomposite material composed of two differentnanometer-sized crystallites would have significantlyhigher contact area between the two compounds, and maytherefore posses an enhanced magneto electric effect. Oneof the most serious problems in the practical application ofnew manganite colossal magnetoresistance (CMR)materials remains to be their in sufficient magnetoresistive(MR) response at room temperature in weak magneticfields, used in most of the potentially interesting devices[1]. Much effort has been made to enhance the propertiesof these materials, such as synthesizing CMR–insulatorcomposites. These extrinsic effects rely on the existence ofan insulating tunneling barrier separating theferromagnetic grains. Such attempts include LCMO BTO[2], LCSMO CoFeR2ROR4R [3] etc and so on. Most of suchresults show enhancement in MR. Our previous work hasshown that making LSMO-based composite provides anefficient way to enhance and control electrical transportand MR [4]. In present report the magnetic and electricproperties of a series of CMR ferroelectric (FE)composites have been studied.A composite series where= 0.0, 0.10, 0.15, 0.20, 0.30 and 0.40 samples wereprepared in two steps. In this process firstly single phaseLCMO was prepared by pyrophoric method. It was thenmixed with fine powder of STO (Alfa Aesar, 99.99%) inrequired ratio and pressed into pellets. The pellets wereResistivity(cm)x=0.40x=0.30x=0.20x=0.10x=0.050 100 150 200 250 300T (K)Figure 1. Temperature variation of resistivity for compositefinally sintered at 900 C in air for 2 hr, and then slowlyfurnace cooled to room temperature..The XRD and SEM analysis exhibits that the compositesconsist of two phases: one is LCMO perovskite phase; theother is STO phase, which clearly indicates thecoexistence of LCMO and STO phases. The variation ofresistivity as a function of temperature in zero fields for allcomposites in the temperature range 10–300K is shown inFigure 1. The parent LCMO sample shows metal- insulator(M-I) transition at a temperaturefollowed bya broad hump. In all grown composites of this series, asmall peak corresponding to M-I transition of parentLCMO occurs at 240K. With the increase of STO contentupto to , decreases and resistivity () atincreases as shown in Figure. But for , a reversetrend is observed, i. e. again increases with a smalldecrease in resistivity. The magnetic phase transitions havebeen studied by the temperature variation of real ()component of AC susceptibility. The LCMO sampleundergoes a PM-FM transition at Tc ~270K. After addition (Arbitrary unit)x=0.40x=0.30x=0.20x=0.10x=0.00 50 100 150 200 250 300T (K)Figure 2. Real part of AC susceptibility for all samplesof BTO, Tc remains almost same indicating thatstoichiometry of LCMO phase within the grains remainsessentially unchanged. Since STO is nonmagnetic in themeasured temperature range, the ferromagnetic order ofthe composites comes up only from LCMO.In summery a nanocomposites series has been preparedby pyrophoric method. From XRD, and SEM results thecoexistence of both the phases has been confirmed. Theparent sample shows a distinct transition at .From resistivity data it is concluded that for this series,conduction threshold occurs at STO content. S.Keshri gratefully acknowledges Department of Scienceand Technology (DST), India for financial assistance. L.Joshi and S. S. Rajput gratefully acknowledge Council ofScientific and Industrial Research and DST, India forproviding fellowship, respectively.* Corresponding author: HTShailendra.phy@gmail.comT[1] Daughton, J-M., 1999. GMR application, J. Magn. Magn. Mater,192: 334-342.[2] Keshri, S., Joshi, L., Rout, S-K., 2009. Influence of BTO phase onstructural, magnetic and electrical properties of LCMO, J. ofAlloys and Compd., 485: 501-506.[3] Xiong, C-S., et al., 2009. Electrical properties and magnetoelectriceffect measurement in La0R.7RCaR0.2RSrR0.1RMnOR3R/xCoFeR2ROR4Rcomposites, J. of Alloys and Compd. 474: 316-320.6th Nanoscience and Nanotechnology Conference, zmir, 2010 750