Local structure and electronic property change in spinel chalcogenides

Abstract

The locallatticedistortionisbelievedtoplayamajorroleforexhibit- ing variousexoticpropertieslikecolossalmagnetoresistance,colos- sal magnetocapacitance,colossalelectroresistance,colossalelectro- capacitance, multiferroicityetcinCdCr2Se4 and CdCr2S4. However, suchobservede ectshavestimulateddebatesontheoriginofrelaxor ferroelectricbehaviourinthesematerialswhichhavemotivatedthe researcherstoworkonthesematerials.Polycrystallinesamplesof CdCr2Se4􀀀xSx with x=0,1,2,3,4 hasbeenpreparedbysolidstatere- action method.Thephasepurityofthepreparedsamplesarecon- rmed bytheX-raydi ractionmeasurement,followedbyRietveld re nementoftheXRDpro le.Thetransportpropertyofthesam- ples arestudiedbyresistivitymeasurementusingfourprobemethod at lowtemperature.Allthepreparedsamplesshowthesemicon- ducting natureandfoundtofollowhoppingconductionprocess.The localstructuredistortionhasbeenobservedinallS-substitutedsam- ples inEXAFSmeasurement.Themagneticpropertiesmeasure- mentrevealsthesamplesareferromagnetic.InACsusceptibility data, anomalyisobservedaboveTC due toshortrangemagnetic clustering (SRMC).Signi cantlocallatticedistortionisobservedin Raman spectra.AnomaliesinpeakpositionandFWHMofRaman modesarealsoobservedintemperaturedependentRamanspectra in theSRMCtemperaturerange.Theexperimentalworkdetailed in thisthesisprovidestheinformationonhowthemagneticprop- ertychangeswithlocallatticedistortionandhowthespin-phonon correlation existsatparamagneticregime.