Proučavanje magnetizma u kagome spoju Cs2Cu3SnF12

master's thesis

• Title (english): Study of magnetism in a kagome compund Cs2Cu3SnF12
• Author: Igor Marković
• Mentor: Mihael Grbić (mentor)
• Committee member: Mihael Grbić (predsjednik povjerenstva)
• Committee member: Matko Milin (član povjerenstva)
• Committee member: Danko Radić (član povjerenstva)
• Committee member: Miroslav Požek (član povjerenstva)
• Committee member: Nikola Poljak (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2015-11-02, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics

Abstract

Kagome antiferomagneti su materijali koji zasada najviše obećavaju kao kandidati za prave kvantne spinske tekućine, čak i na temperaturi apsolutne nule. Visoki stupanj frustracije koji unosi kagome struktura ih stvara idealnim poligonom za fundamentalna istraživanja na područjima kvantnog magnetizma te kvantnih kritičnih pojava. Jedan takav spoj, Cs2Cu3SnF12, koji na TN = 20 K prelazi u svojevrsno Neelovo uređeno stanje, smo u ovom radu istraživali koristeći tehnike nuklearnih spinskih rezonancija. Rad je započeo NMR mjerenjima na ceziju, ali je iz dobivenih spektara i spore spin-rešetka relaksacije zaključeno da su cezijevi atomi preslabo vezani na magnetske stupnjeve slobode koje želimo promatrati da bili korisni kao metoda karakterizacije. Mjerenja su zatim preseljena na jezgre bakra tako da i nuklearni spin metode i elektronski spin koji želimo karakterizirati leže na istom atomu. Magnetsko osnovno stanje uzorka je okarakterizirano snimljenom temperaturnom ovisnosti spektra te je uz pomoć računalne simulacije spektra sugerirana njegova struktura. Spin-rešetka relaksacijsko vrijeme je iskorišteno za promatranje kritičnog ponašanja na temperaturama iznad prijelaza dok je cijepanje linija iskorišteno u Neelovoj fazi. Iz tog cijepanja su pomoću prilagodbe kritičnog ponašanja dobiveni kritični eksponenti za pojedinu liniju koji su se pokazali konzistentnima s uređivanjem Heisenbergovih spinova. Konačno, ovaj rad predstavlja samo dio mjerenja većeg projekta kojem je konačni cilj usporedbom ovih rezultata s onima pod primijenjenim vanjskim tlakom pokazati postojanje kvantnog faznog prijelaza u magnetski neuređeno stanje.

Abstract (english)

Kagome antiferromagnets are the most promising candidates for real quantum spin liquids, even at absolute zero temperature. The high degree of frustration that the kagome structure introduces makes them ideal subjects for fundamental research in quantum magnetism and quantum criticality. We have researched one such compound, Cs2Cu3SnF12, which turns to a Neel-like ordered state at TN = 20 K, using nuclear spin resonance techniques. We began with Cs NMR measurements but abandoned them due to poor coupling of caesium nuclei with the desired magnetic degrees of freedom, which was revealed both in the measured spectra and slow spin-lattice relaxation. Measurements were then refocused on copper nuclei so that both the method’s probe spin and the electron spin we wish to characterise lie on the same atom. The magnetic ground state of the sample was mainly characterised by the temperature dependence of the spectrum while the computer simulation we ran gave an indication for it’s structure. Spin-lattice relaxation time was used to observe the critical behaviour on temperatures above the transition while the line splitting was use within the Neel phase. Fitting critical behaviour curve to that line splitting gave us critical exponents for each line which were consistent with Heisenberg spin ordering. Finally, the work done for this thesis is still in progress and represents only part of a bigger project whose final goal is to show the existence of a pressure induced quantum phase transition to the magnetically ordered state by comparing these results with the ones that will be done under applied pressure.

• Keywords: kagome antiferomagneti; nuklearne spinske rezonancije; NQR; NMR
• Keywords (english): kagome antiferromagnets; nuclear spin resonance; NQR; NMR
• Language: croatian
• URN:NBN: urn:nbn:hr:217:447354
• 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: 2017-04-04 20:42:34