Utjecaj ligandnog okruženja i dimenzionalnosti kristalne rešetke na magnetsku anizotropiju iona 3d prijelaznih metala

doctoral thesis

• Title (english): Influence of ligand surrounding and crystal lattice dimensionality on the magnetic anisotropy of 3d transition metal ions
• Author: Mirta Herak
• Mentor: Marko Miljak (mentor)
• Committee member: Krešo Zadro (predsjednik povjerenstva)
• Committee member: Marko Miljak (član povjerenstva)
• Committee member: Ivo Batistić (član povjerenstva)
• Granter: University of Zagreb; Faculty of Science; (Department of Physics); Zagreb
• Defense date and country: 2009-11-05, Croatia
• Scientific / art field, discipline and subdiscipline: NATURAL SCIENCES; Physics
• Universal decimal classification (UDC): 53 - Physics

Abstract

Eksperimentalnim tehnikama mjerenja magnetske susceptibilnosti i momenta sile istraživana su magnetska svojstva niskodimenzionalnih sustava CuGeO3 i CuSb2O6, trodimenzionalnih sustava Bi2CuO4 i Cu3TeO6 , te Cu2Te2O5X2 (X=Cl, Br). Magnetizam ovim materijalima daje ion Cu2+ čiji nespareni elektron u 3d ljusci ima spin S=1/2. U spin - Peierls sustavu CuGeO3 defekti (<1%) pri niskim temperaturama daju doprinos susceptibilnosti koji slijedi zakon χdef = AT-α s α ≈ 0.7, što ukazuje na razbijanje regularnih lanaca i postojanje više različitih energija izmjene na lancu. U jednodimenzionalnom CuSb2O6 koji se ureduje antiferomagnetski (AFM) pri niskim temperaturama određena je jakost međulančane interakcije Jinter u odnosu na intralančanu, J, Jinter = 0.05 J te je detektirana mala anizotropija energije izmjene J od 1%. Kombinacijom mjerene kutne ovisnosti momenta sile i fenomenološkog pristupa energiji anizotropije pokazano je da je simetrija AFM uređenog stanja u Bi2CuO4 opisana anizotropijom lake ravnine koja daje dvije okomite spinske (S) domene, a ne anizotropijom lake osi. Sličnim pristupom je pokazano da je AFM uredeno stanje u Cu3TeO6 sustavu s novim tipom 3D magnetske rešetke opisano kubičnom simetrijom s četiri AFM S domene. U Cu2Te2O5X2 (X=Cl, Br) sustavu s kristalografski nezavisnim tetraedrima spinova rezultati mjerenja ukazuju na postojanje Dzyaloshinskii-Moriya anizotropne interakcije. Kutna ovisnost momenta sile u AFM uređenom stanju pokazuje da postoje AFM domene koje se mogu repopulirati malim magnetskim poljima. Efektivni magnetski moment u X=Br je manji od momenta u X=Cl.

Abstract (english)

The magnetic properties of the low-dimensional CuGeO3 and CuSb2O6, three-dimensional Bi2CuO4 and Cu3TeO6 , and of Cu2Te2O5X2 (X=Cl, Br) were investigated by the dc magnetic susceptibility measurement and torque magnetometry. Magnetism in these compounds comes from Cu2+ ion with an unpaired electron with spin S = 1/2 in a 3d shell. In spin - Peierls system CuGeO3 a small amount of defects was detected with the susceptibility following the χdef = AT-α law at low temperatures with a α ≈ 0.7. This suggests breaking of regular chains and existence of more than one exchange energy on the chain. In the one - dimensional CuSb2O6 which orders antiferromagnetically (AFM) the interchain interaction Jinter is weak compared to the intrachain J, Jinter = 0.05 J, and the anisotropy of the exchange energy is also small, 1%J. A combination of the measured angular dependence of torque and phenomenological approach to the anisotropy energy shows that the symmetry in Bi2CuO4 is described by the easy plane anisotropy with two perpendicular spin (S) domains, and not the easy axis anisotropy. Similar approach shows that Cu3TeO6, a system with a new type of 3D magnetic lattice, has cubic symmetry in the AFM state with four AFM S domains. In Cu2Te2O5X2 (X=Cl, Br) systems with the crystallographically isolated spin tetrahedra the Dzyaloshinskii-Moriya anisotropic interaction is detected. The AFM ordered state has two perpendicular AFM domains which can be repopulated by applying the magnetic field. The effective magnetic moment is smaller for X=Br than X=Cl.

• Keywords: magnetska susceptibilnost; magnetska anizotropija; spojevi bakrenih oksida; niskodimenzionalne rešetke; ligandno okruženje magnetskih iona; superizmjena
• Keywords (english): magnetic susceptibility; magnetic anisotropy; copper oxides; low dimensional lattices; ligand surrounding of magnetic ions; superexchange
• Language: croatian
• URN:NBN: urn:nbn:hr:217:042437
• Study programme: Title: Physics; Study programme type: university; Study level: postgraduate; Academic / professional title: doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika (doktor/doktorica znanosti, područje prirodnih znanosti, polje fizika)
• Type of resource: Text
• Extent: 183 str.
• File origin: Born digital
• Access conditions: Open access
• Created on: 2017-08-24 11:55:43