Študij lokalnih magnetnih lastnosti spojine YCu3(OH)6Cl3 z jedrsko magnetno resonanco

Keber, Črt (author), Zorko, Andrej (mentor)

V zaključni nalogi bom predstavil spojino YCu3(OH)6Cl3, njeno strukturo in magnetne lastnosti. Spojina je predstavnik tako imenovane spinske mreže kagome. V taki mreži so spini geometrijsko frustrirani, kar pomeni, da geometrija mreže ne omogoča, da bi bile vse spinsko-spinske izmenjalne interakcije istočasno minimizirane. Namen zaključne naloge je bil določiti tenzor hiperfine sklopitve med 35Cl jedri in elektroni na Cu2+ ionih in določiti, kako se lokalna magnetna susceptibilnost spreminja s temperaturo. NMR spektre 35Cl sem pomeril pri temperaturah od 8 K do 291 K. Jedra klora se v mreži nahajajo na dveh različnih mestih, ki si med sabo nista ekvivalenta. V spektru sem zato moral določiti, kateri vrhovi pripadajo kateremu mestu. Iz razdalje med satelitskimi prehodi sem določil kvadrupolno frekvenco v odvisnosti od temperature. V programskem jeziku Python in C sem napisal simulacijo spektrov. Z metodo Monte Carlo sem prilegal simulirane spektre izmerjenim in tako določil razmerje komponent tenzorja hiperfine sklopitve in temperaturno odvisnost tenzorja magnetne susceptibilnosti. Izračunal in prikazal sem Knightov premik, ter izračunal tenzor hiperfine sklopitve. S pomočjo tenzorja hiperfine sklopitve sem izračunal lokalne vrednosti magnetne susceptibilnosti v odvisnosti od temperature in jih primerjal z makroskopskimi vrednostmi. Ugotovil sem, da pride pri nizkih temperaturah do precejšnjega razhajanja med lokalnimi in makroskopskimi vrednostmi in da je lokalna magnetna susceptibilnost precej anizotropna, kar je znak prisotnosti znatne magnetne anizotropije.

• Language: Slovenian
• Keywords: YCu3(OH)6Cl3, spinska mreža kagome, geometrijska frustracija, hiperfina interakcija, kvadrupolna interakcija, tenzor hiperfine sklopitve, magnetna susceptibilnost, Knightov premik, jedrska magnetna resonanca, spinski odmev
• Work type: Final paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2020
• PID: 20.500.12556/RUL-121516
• COBISS.SI-ID: 31583235
• Publication date in RUL: 13.10.2020

Secondary language

• Language: English
• Title: Study of local magnetic properties of the YCu3(OH)6Cl3 compound using nuclear magnetic resonance

Abstract

In this thesis, I will present the YCu3(OH)6Cl3 compound, its structure and magnetic properties. This compound is a realization of the kagome spin lattices. In such a lattice spins are geometrically frustrated, which means that geometry of the lattice does not allow all of spin-spin interactions to be minimized instantaneously. The goal of this thesis was to determine the hyperfine coupling tensor between the 35Cl nuclei and the electrons on Cu2+ ions and to determine how local magnetic susceptibility changes with temperature. I measured NMR spectra of 35Cl nuclei at temperatures between 8 K and 291 K. The chlorine nuclei occupy two different sites in the crystal lattice that are not equivalent. Therefore, first I had to determine which peeks in the spectrum belong to which site. From the distance between the satellite transitions I was able to determine the temperature dependence of the quadrupole frequency. In programming languages Python and C I programmed spectrum simulations. With the Monte Carlo methode I fitted the simulated spectrum to measurements and determined the ratio between the main components of the hyperfine coupling tensor as well as determine temperature dependence of the magnetic susceptibility tensor. I calculated and showed the Knight shift and calculated hyperfine coupling tensor. With the help of the hyperfine coupling tensor I calculated values of the local magnetic susceptibility as a function of temperature and compared them with macroscopic measurements. I found a large discrepancy between the local and bulk values of the magnetic susceptibility at low temperatures and a lorge anisotropy of the local magnetic susceptibility, the latter being a fingerprint of sizable magnetic anisotropy.

• Keywords: kagome spin lattice, geometrical frustration, hyperfine interaction, hyperfine coupling tensor, magnetic susceptibility, Knight shift, nuclear magnetic resonance, spin echo, Monte Carlo simulation