Meritve magnetnih lastnosti ikozaedričnih kvazikristalov Zn–Mg–Ho tipov P in F

Močnik, Žan (author), Koželj, Primož (mentor)

Kvazikristali so urejene snovi, ki pa nimajo diskretne translacijske simetrije, značilne za običajne periodične kristale. Kljub temu imajo ostre difrakcijske vrhove, njihova struktura pa lahko vsebuje tudi simetrije, ki pri periodičnih kristalih niso dovoljene, kot so petštevna, desetštevna in dvanajstštevna simetrija. Cilj zaključne naloge je magnetna karakterizacija dveh tipov ikozaedričnih kvazikristalov v sistemu Zn-Mg-Ho, tipa P in F. S pomočjo SQUID magnetometra MPMS3 smo izvedli meritve magnetnega odziva v magnetnem polju do 7 T v temperaturnem razponu od 1,8 K do okoli 290 K. Meritve smo dopolnili z meritvami vse do 0,4 K s pomočjo kriostata na $^3$He, da bi lahko opazili magnetne prehode, ki jih nismo opazili pri višjih temperaturah. Poleg magnetnih meritev analiziramo tudi meritve specifične toplote v odvisnosti od temperature, izvedene z merilno napravo PPMS 9T. Meritve za oba tipa kvazikristalov sem na koncu analiziral ter na kratko primerjal, s ciljem, da bi ugotovil morebitne razlike med njunimi magnetnimi lastnostmi. Ugotovili smo, da sta oba tipa kvazikristalov spinski stekli, torej pod temperaturo zamrznitve $T_f$ pride do zamrznitve spinskih magnetnih momentov v prostoru. Iz prilagajanja na meritve magnetne susceptibilnosti sem določil Curiejeve konstante $C$ in Curie-Weissove temperature $\theta$. Iz $C$ izračunana efektivna magnetna momenta $m_\text{ef}$ sta za oba tipa v okviru merske napake enaka in enaka referenčni vrednosti. Izračunane $\theta$ so negativne, kar kaže na prevlado antiferomagnetnih interakcij.

• Language: Slovenian
• Keywords: kvazikristali, aperiodični kristali, spinska stekla, magnetizem, histerezne zanke, magnetna susceptibilnost, specifična toplota, meritve lastnosti snovi do kriogenih temperatur
• Work type: Final paper
• Typology: 2.11 - Undergraduate Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Year: 2026
• PID: 20.500.12556/RUL-188194
• COBISS.SI-ID: 293109763
• Publication date in RUL: 19.09.2026

Secondary language

• Language: English
• Title: Measurements of magnetic properties of F and P-type Zn–Mg–Ho icosahedral quasicrystals

Abstract

Quasicrystals are ordered materials, which lack the discrete translational symmetries typical for ordinary periodic crystals. Despite this they have sharp diffraction peaks while at the same time containing symmetries that are forbidden in periodic crystals, for example five-, ten- and twelvefold symmetry. The aim of this final thesis was the magnetical characterization of two types of icosahedral Zn-Mg-Ho quasicrystals, namely crystals of P and F type. Using the MPMS3 SQUID magnetometer we performed measurements of the magnetic response in magnetic fields up to 7 T and in the temperature range from 1.8 K to around 290 K. We supplemented the measurements with further measurements down to 0.4 K using a $^3$He cryostat in order to observe any magnetic transitions which we might have missed at higher temperatures. In addition to magnetic measurements we analysed also temperature dependence of specific heat measurements performed on a Quantum Design PPMS 9T. I analysed measurements of both types of quasicrystals and briefly compared them in order to ascertain any potential differences between the two types of quasicrystals. We determined that both types of quasicrystals are spin glasses, in other words below the spin freezing temperature $T_f$ a gradual freezing of the magnetic moments occurs. From fits to the magnetic susceptibility measurements I determined the Curie constant $C$ and the Curie-Weiss temperature $\theta$. The effective magnetic moments determined from $C$ are equal within the experimental error and equal to the reference value. The negative calculated $\theta$s are negative, indicative of predominantly antiferromagnetic interactions.

• Keywords: quasicrystals, aperiodic crystals, spin glasses, magnetism, hysteresis loops, magnetic susceptibility, specific heat, measurements of material properties down to cryogenic temperatures