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| Author(s): |
Vinicius Tadeu Santana
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT) |
| Defense date: | 2016-09-26 |
| Examining board members: |
Otaciro Rangel Nascimento;
Eduardo Ribeiro de Azevêdo;
Oswaldo Baffa Filho;
Rafael Calvo;
Maria Oswald Machado de Matos
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| Advisor: | Otaciro Rangel Nascimento |
| Abstract | |
In this work, two transition metal oxides presenting long range magnetic order and a plastdoped polyaniline were investigated via electron paramagnetic resonance. Polycrystalline samples of the multiferroic manganese oxide, BiMn2O5, showed antiferromagnetic resonance modes which were identified from high magnetic fields multi frequency electron paramagnetic resonance. These data were fitted according to Yosida and Nagamiya theory of antiferromagnetic resonance. The macroscopic constants of magnetic anisotropy K1=7.0 x 108 emu Oe mol1 and K2=3.9 x 108 emu Oe mol1 were obtained from this fitting and allowed for estimating the microscopic constant of anisotropy. Magnetic anisotropy may lead to magnetoelasticity, which is related to the ferroelectricity in this material. Thus, the characterization of this physical quantities may be useful to future research. Single crystals of a homometallic iron ludwigite, Fe3O2BO3, were investigated in its distinct magnetic phases. This system has two independent iron sub-lattices which order magnetically in two distinct temperatures, presenting electronic correlations from room temperature. Despite the broad and superposed lines in the EPR spectra, the presence of such correlations was demonstrated in one of these structures, which is known as three leg ladders (3LL). A dimer Fe3+-Fe2+ was identified at room temperature, showing an antiferromagnetically coupled state subjected to double exchange interactions. The charge transfer integral b was estimated. Temperature sweep EPR measurements in films of plastdoped polyanilines suggested the population and depopulation if a triplet state typical of spin 1 dimers. Differences in the parameters after thermal cycling suggested the freezing of the structure at different states in accordance to observed thermocromism in these polymers. In conclusion, the relevance of the EPR technique was demonstrated to the characterization of exchange coupled systems. (AU) | |
| FAPESP's process: | 12/24827-9 - Electronic spin resonance in systems with antiferromagnetic interactions: multiferroics, conducting polymers and ludwigites |
| Grantee: | Vinicius Tadeu Santana |
| Support Opportunities: | Scholarships in Brazil - Doctorate |