Magnetotransportna svojstva anizotropnih organskih vodiča (TMTTF)2ReO4 i α-(BEDT−TTF)2 I3

master's thesis

• Title (english): Magnetotransport properties ofanisotropic organic conductors (TMTTF)2ReO4 an alpha-(BEDT-TTF)2I3
• Author: Branimir Mihaljević
• Mentor: Mario Basletić (mentor)
• Committee member: Mario Basletić (predsjednik povjerenstva)
• Committee member: Bojana Hamzić (član povjerenstva)
• Committee member: Danko Radić (član povjerenstva)
• Committee member: Emil Tafra (član povjerenstva)
• Committee member: Ivo Batistić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2014-09-29, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

U ovom su radu izloženi rezulti mjerenja otpora, magnetootpora i Hallovog efekta na anizotropnim organskim vodičima (TMTTF)2ReO4 i α- (BEDT−TTF)2I3. Mjerenja su vršena u rasponu temperatura od 140 K, odnosno 60 K do sobne temperature i u magnetskim poljima do 5 T. Rezultati mjerenja otpora (TMTTF)2ReO4 pokazuju očekivano ponašanje sa dva vidljiva fazna prijelaza uzrokovana uredenjem aniona na nižim te uredenjem naboja na višim temperaturama. Izmjerena ovisnost Hallove konstante o temperaturi usporedena je s izmjerenom ovisnošću otpora o temperaturi. Korišten je najjednostavniji, klasični teorijski model koji omjer dobivenih ovisnosti povezuje s promjenom razlike pokretljivosti šupljina i elektrona (μh − μe), a dobivene vrijednosti magnetootpora s umnoškom pokretljivosti (μhμe). Teorijski izrazi izvedeni u ovom radu pokazuju povezanost Hallove konstante, otpora i magnetootpora, te omogućuju izračunavanje vrijednosti pokretljivosti i koncentracije nosioca naboja koja se razlikuje od standardne procjene za čak tri reda veličine. Rezultati mjerenja otpora α-(BEDT−TTF)2I3 pokazuju očekivano ponašanje s naglašenim metal-izolator faznim prijelazom. Izmjerena ovisnost Hallove konstante o temperaturi usporedena je s izmjerenom ovisnošću otpora o temperaturi te je uočena približna proporcionalnost. Za temperature iznad faznog prijelaza uočeno je vrlo dobro slaganje izmjerenih vrijednosti Hallove konstante, a time i proračunatih vrijednosti koncentracije naboja s teorijski predvidenim vrijednostima za metalnu fazu dobivenim iz vrijednosti parametara kristalne rešetke. Isto teorijsko predvidanje pokazalo se približno dobro i u (TMTTF)2ReO4. Primjećena je promjena predznaka Hallove konstante u α-(BEDT−TTF)2I3 ispod temperature faznog prijeleza što ukazuje na veću pokretljivost elektrona spram pokretljivosti šupljina u izolatorskoj fazi.

Abstract (english)

In this thesis we present the measurements of resistance, magnetoresistance and Hall effect of the anisotropic organic conductors (TMTTF)2ReO4 and α-(BEDT−TTF)2I3 ˙ Measurements were conducted in temperature range from 140 K i.e. 60 K respectively, to room temperature and in magnetic fields to 5 T. The results of (TMTTF)2ReO4 resistivity show the expected behavior with two visible phase transitions caused by anion ordering at lower, and charge ordering at higher temperatures. The temperature dependence of Hall constants is compared with the measured temperature dependence of resistance. We use the simplest, classical theoretical model which relates the ratio of measured dependencies with changes in difference between hole and electron mobilities (μh − μe), and also the values of magnetoresistance with product of mobilities (μhμe). Theoretical expressions derived in this work show the connection between Hall constant, resistance and magnetoresistance and also enable the calculation of charge carriers mobility and concentration which differs from standard estimate for three orders of magnitude. Measurement results of α- (BEDT−TTF)2I3 resistivity show the expected behavior with metal-insulator phase transition. The temperature dependence of Hall constants is compared with the temperature dependence of resistance and we found that they are approximatly proportional. For temperatures above the phase transition, values of Hall constants, and thereby also carrier concentrations are in very good agreement with the theoretically predicted values for metallic phase, obtained from the values of crystal lattice parameters. The same theoretical predictions also proved to be relatively good for (TMTTF)2ReO4. We found sign change of Hall constant in α-(BEDT−TTF)2I3 under phase transition temperature, indicating the higher electron mobility versus hole mobility in insulator phase.

• Keywords: magnetotransportna svojstva; anizotropni organski vodiči; Hallova konstanta
• Keywords (english): magnetotransport properties; anisotropic organic conductors; Hall constant
• Language: croatian
• URN:NBN: urn:nbn:hr:217:547658
• Study programme: Title: Physics; specializations in: Research; Course: Research; Study programme type: university; Study level: integrated undergraduate and graduate; Academic / professional title: magistar/magistra fizike (magistar/magistra fizike)
• Type of resource: Text
• File origin: Born digital
• Access conditions: Access restricted to students and staff of home institution
• Created on: 2017-06-14 15:59:55