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Synthesis and characterisation of layered magnetic oxalato-salts

Watts, Ian Donald; (2000) Synthesis and characterisation of layered magnetic oxalato-salts. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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This thesis describes the synthesis and characterisation of magnetic oxalato-salts of general formula AMᴵᴵMᴵᴵᴵ(C₂O₄)₃, where A is a monovalent organic cation and Mᴵᴵ and Mᴵᴵᴵ are transition metals. Compounds of this type crystallise as honeycomb layers of metal-oxalate sheets interleaved by layers of the cation and may be considered quasi two-dimensional molecular-based magnets. The compounds considered are derived from FeᴵᴵFeᴵᴵᴵ and MnᴵᴵFeᴵᴵᴵ with the cations tetraphenylphosphonium, tetrabutylammonium and alkyltriphenylphosphonium, where the alkyl chain ranges from propyl to heptyl inclusive. Structural characterisation by powder X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) is presented; lattice parameters at room temperature have been determined from XRD and the temperature-dependence of the local structure around the metal ions has been investigated by EXAFS on (n-C₄H₉)₄NFeFe(C₂O₄)₃, (n-C₄H₉)₄NMnFe(C₂O₄)₃, PPh₄FeFe(C₂O₄)₃ and PPh₄MnFe(C₂O₄)₃ (PPh₄ = tetraphenylphosphonium). Bulk magnetic behaviour has been studied by DC magnetometry. Magnetic data in the paramagnetic regime have been fitted to the Curie-Weiss law enabling Curie and Weiss constants to be determined. Variation of the magnetic behaviour by changing the organic cation and by dilution of the magnetic centers with the diamagnetic ions Znᴵᴵ and Gaᴵᴵᴵ has been investigated. The local magnetic properties of (n-C₄H₉)₄NFeFe(C₂O₄)₃ and PPh₄MnFe(C₂O₄)₃ have been probed by muon spin relaxation. The magnetic structure of deuterated examples of PPh₄MnFe(C₂O₄)₃ and PPh₄FeFe(C₂O₄)₃ has been studied by polarised neutron diffraction. The temperature-dependence of the two-dimensional magnetic correlation length has been determined by fitting these data to a Warren peak shape function.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Synthesis and characterisation of layered magnetic oxalato-salts
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Oxalato-salts
URI: https://discovery.ucl.ac.uk/id/eprint/10106320
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