Παρασκευή περοβσκιτών μαγγανίου μικτού σθένους και μελέτη των ηλεκτρονιακών και μαγνητικών ιδιοτήτων τους
| dc.contributor.author | Ασαρίδης, Ηλίας Σ. | el |
| dc.date.accessioned | 2023-06-02T14:08:09Z | |
| dc.date.available | 2023-06-02T14:08:09Z | |
| dc.identifier.uri | https://olympias.lib.uoi.gr/jspui/handle/123456789/32835 | |
| dc.identifier.uri | http://dx.doi.org/10.26268/heal.uoi.12636 | |
| dc.rights | Attribution-NonCommercial-NoDerivs 3.0 United States | * |
| dc.rights | info:eu-repo/semantics/openAccess | * |
| dc.rights.uri | http://creativecommons.org/licenses/by-nc-nd/3.0/us/ | * |
| dc.subject | Περοβσκίτες | el |
| dc.subject | Μαγνητοαντίσταση | el |
| dc.subject | Φασματοσκοπία Mössbauer | el |
| dc.subject | Ακτίνες Χ | el |
| dc.subject | Μαγνητικά συμπλέγματα | el |
| dc.title | Παρασκευή περοβσκιτών μαγγανίου μικτού σθένους και μελέτη των ηλεκτρονιακών και μαγνητικών ιδιοτήτων τους | el |
| dc.type | doctoralThesis | * |
| dc.type | info:eu-repo/semantics/doctoralThesis | * |
| heal.abstract | In the present thesis, the magnetic phase diagram of manganese perovskites Lao.67-ySro.33+yMni_xSnx0 3 , Lao.67-yBao33+yMni_xSnx03 and Lao.67-yCao.33+yMni-xSnx0 3, with x=0.01, 0.02 and y=0, 0.07 has been investigated. Manganese perovskites are systems with remarkable electronic and magnetic properties. A variety of experiments revealed a very rich phase diagram. Their most notable property is the colossal decrease of resistivity by the application of an external magnetic field (CMR) near the critical temperature, where the system undergoes a phase transition from a paramagnetic (PM) to a ferromagnetic (FM) phase. Several studies have focused on the critical behaviour in the temperature region where this takes place in order to investigate its nature (first or second order) and to derive critical exponents in the latter case. Scaling plots based on the measurement of magnetic isotherms near the critical temperature have been used in order to derive the critical exponents and verify the second order type of the transition. In order to study the phase transition from a paramagnetic (PM) to a ferromagnetic (FM) phase at microscopic level, Mossbauer measurements in zero external magnetic field were performed. Coexistence of FMM (Ferromagnetic-Metal) and FMI (Ferromagnetic-Insulator) states was found at the temperatures near the critical point. This behaviour may play a key role in the appearance of colossal magnetoresistance in manganese perovskites. It is probable that by applying an external magnetic field close to the critical point, Tc, the number and size of FMI regions are drastically reduced, enhancing thus conductivity. X-ray powder diffraction diagrams show that the structure can be described by a rhombohedral unit cell (space group R-3C) for the samples where the A-site is occupied by La and Sr or La and Ba ions and a orthorhombic unit cell (space group Pnma) for the samples where the A- site is occupied by La and Ca ions. An increase of the cell volume is observed as the Mn is substituted by Sn ions in all samples. The six-coordinated Mn4+ is replaced by Sn4+, which has higher ionic radius (Mn4+:0.53 A, Sn4+: 0.69 A), therefore an increase in the lattice constants and the unit cell volume is expected, owed mainly to the difference in ionic radii. As a result of the Mn3+/4+ substitution by Sn4+, a decrease of the transition temperature is observed, which is mainly attributed to the suppression of the double-exchange (DE) mechanism due to the existence o f non-magnetic impurities. Arrott end scaling plots show that the samples, where the A-site is occupied by La and Sr or La and Ba ions, follow the behaviour o f the conventional second-order ferromagnetic transition. The values of the critical exponents (β, γ) are between those predicted by the three-dimensional Heisenberg (β=0.365 γ=1.38) model and the mean field theory (β=0.5, γ=1.0). In contrast, the samples that contain La and Ca ions at the A-site show anomalous behaviour around Curie point. | en |
| heal.academicPublisher | Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών. Τμήμα Φυσικής | el |
| heal.academicPublisherID | uoi | el |
| heal.access | free | el |
| heal.advisorName | Μπάκας, Θωμάς | el |
| heal.committeeMemberName | Παναγιωτόπουλος, Ιωάννης | el |
| heal.committeeMemberName | Μπάκας, Θωμάς | el |
| heal.committeeMemberName | Μουκαρίκα, Αλίκη | el |
| heal.committeeMemberName | Κοσμίδης, Κωνσταντίνος | el |
| heal.committeeMemberName | Πομώνης, Φίλιππος | el |
| heal.committeeMemberName | Καμαράτος, Ματθαίος | el |
| heal.committeeMemberName | Ασημακόπουλος, Παναγιώτης | el |
| heal.dateAvailable | 2023-06-02T14:09:09Z | |
| heal.fullTextAvailability | true | |
| heal.language | el | el |
| heal.numberOfPages | 170 σ. | el |
| heal.publicationDate | 2006 | |
| heal.recordProvider | Πανεπιστήμιο Ιωαννίνων. Σχολή Θετικών Επιστημών | el |
| heal.type | doctoralThesis | el |
| heal.type.el | Διδακτορική διατριβή | el |
| heal.type.en | Doctoral thesis | en |
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