Antiferromagnetically ordered state in spin tetramer system SeCuO3

Abstract

U ovom radu proučavana su svojstva antiferomagnetski uređenog stanja u sustavu spinskih tetramera SeCuO3. Antiferomagnetski upredeno stanje nastaje ispod Néelove temperature TN = 8 K, a proučavano je metodom mjerenja magnetskog momenta sile u magnetskim poljima H ≤ 4:5 T pri temperaturama nižim od Néelove. Magnetski moment sile osjetljiv je na magnetsku anizotropiju čitavog uzorka, te mjerenjima kutne ovisnosti moguće je odrediti simetriju uređenog stanja za jednostavnije oblike dugodosežnog magnetskog uređenja. Koristeći elemente simetrije pripadne kristalne strukture konstruirali smo oblik magnetokristalne energije te ga iskoristili u fenomenološkom pristupu za opis magnetske anizotropije i spinskih reorijentacija u konačnom magnetskom polju u SeCuO3. Pri tome smo pretpostavili da je uređenje jednostavno jednoosno antiferomagnetsko kako je predloženo u literaturi. Dobiveni rezultati simulacija dobro se slažu s eksperimentom no postoje neka odstupanja koja ukazuju na kompliciranije magnetsko uređenje te pozivaju na daljnja istraživanja magnetske strukture ovog sustava.In this master thesis we studied properties of antiferromagnetically ordered state of spin tetramer system SeCuO3. This system orders antiferromagnetically below Néel temperature. We studied this state using torque magnetometry in magnetic fields H ≤ 4:5 T at temperatures lower than TN. Magnetic torque is sensitive to magnetic anisotropy of the sample, and by measuring angular dependence one can determine the symmetry of the magnetically ordered state for some simple long-range order. Applying symmetry elements of the crystal structure we construct magnetocrystalline energy which we use in phenomenological approach to describe magnetic anisotropy and spin reorientations in finite magnetic field in SeCuO3. In this approach simple uniaxial antiferromagnetic order as suggested in literature. Simulation results are in good agreement with experiment, however there are some discrepancies which to more complicated magnetic order and call for further investigation of magnetic structure of this system