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Orientadores: Kleber Roberto Pirota, Pascoal José Giglio Pagliuso Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin Resumo: Materiais com dimensões nanométricas podem ter alteradas drasticamente suas propriedades físicas se comparados com a versão volumétrica. Nesses sistemas, as propriedades físicas mostram efeitos de dimensionalidade reduzida, coordenação reduzida de átomos na superfície e presença de alguns efeitos quânticos que dominam em baixas dimensões. Também, mudanças podem surgir quando as dimensões do sistema passam a ser comparáveis com o comprimento característico envolvido com o fenômeno físico estudado. Deste modo, a nanotecnologia proporciona a oportunidade de adaptar novos materiais com características melhoradas ou totalmente novas. Junto com o interesse prático, o crescimento de nanomateriais é também de grande interesse científico fundamental. Neste trabalho, apresentamos os detalhes de um novo método de crescimento de nanofios, desenvolvido no decorrer desta tese, e sua aplicação no estudo de três sistemas com propriedades magnéticas determinadas por diferentes tipos de interação entre elétrons: o intermetálico GdIn3, onde a interação RKKY entre os elétrons "4" f é responsável pelo ordenamento magnético de longo alcance; o metamagneto itinerante Fe3Ga4, onde as flutuações de densidade de spin são responsáveis pelo surgimento de transições entre estados magneticamente ordenados; e o supercondutor elementar Ga, que apresenta valores diferentes de temperatura crítica para suas diversas fases polimórficas. A nova rota de crescimento proposta, nomeada nanonucleação por fluxo metálico, consiste na junção de dois métodos conhecidos: a anodização do alumínio, para obtenção de moldes de alumina nanoporosos; e o método de fluxo metálico, utilizado para o crescimento de monocristais volumétricos de materiais intermetálicos. Em um primeiro passo, medidas de magnetização para o sistema GdIn3 indicam que a interação entre os spins dos elétrons 4f do Gd3+ e os spins dos elétrons de condução não permanece a mesma com a redução da dimensionalidade (nanofios com diâmetro "d ~ 200 nm" ), em acordo com dados de ressonância de spin eletrônico. Por outro lado, o diagrama de fases magnéticas H-T do composto Fe3Ga4, construído a partir de medidas de magnetização, calor específico e resistividade elétrica, muda consideravelmente quando este se apresenta na forma de nanofio ("d ~ 250 nm" ). Finalmente, para o sistema Ga, a condição geométrica particular (nanofios com "d ~ 140 nm" ) favorece a nucleação da fase "? - Ga" com propriedades de um supercondutor tipo II de acoplamento fraco. Os resultados obtidos têm mostrado a grande efetividade do método desenvolvido para produzir sistemas de baixa dimensionalidade com propriedades físicas não previstas. Além disso, a nova rota proposta abre a possibilidade de crescer o nanofio e seu volumétrico correspondente em uma única etapa Abstract: Materials with nanometric dimensions can have their physical properties dramatically altered compared to the bulk version. In these systems, the physical properties present reduced dimensionality effects, decreased atoms coordination at the surface and presence of some quantum effects that dominate in low dimensions. Changes may also arise when the system dimensions become comparable with the characteristic length involved in the physical phenomenon investigated. Therefore, nanotechnology provides the opportunity to adapt new materials with improved or totally new features. Along with the practical interest, the growth of nanomaterials is also of great scientific interest. In this work, we present the details of a new method of nanowire growth, developed during this thesis, and its application in the study of three systems with magnetic properties determined by different types of interaction between electrons: the intermetallic GdIn3, where the RKKY interaction between the 4f electrons is responsible for the long-range magnetic order; the itinerant metamagnet Fe3Ga4, where the spin density fluctuations are responsible for the apparition of transitions between magnetically ordered states; and the elemental superconductor Ga, which presents different critical temperature values for its various polymorphic phases. The new proposed growth route, named metallic-flux nanonucleation, consists in the junction of two known already methods: the aluminum anodization, to obtain nanoporous alumina templates; and the metallic flux method, used for bulk single crystals growth of intermetallic materials. In a first step, magnetization measurements for the GdIn3 system indicate that the interaction between the Gd3+ 4f electron spins and the conduction electron spins does not remain the same with the dimensionality reduction (nanowires with diameter "d ~ 200 nm" ), according to electron spin resonance data. On the other hand, the H-T magnetic phase diagram of the Fe3Ga4 compound, constructed from magnetization, specific heat and electrical resistivity measurements, considerably changes for nanowires case ("d ~ 250 nm" ). Finally, for the Ga system, the special geometric condition (nanowires with "d ~ 140 nm" ) favors the nucleation of the "? - Ga" phase with properties of a weak coupling type-II superconductor. The obtained results have shown the great effectiveness of the developed method for producing low dimensionality systems with unexpected physical properties. In addition, the new proposed route opens the possibility of growing both the nanowire and its bulk corresponding in a single step Doutorado Física Doutora em Ciências CNPQ 148758/2012-6

Agradecimentos: The authors would like to thank the LME/LNNano/CNPEM for technical support during electron microscopy work. This work was supported by the Brazilian funding agencies FAPITEC-SE (PRONEX), CNPq (303910/2015-1 and 455970/2014-9) and the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001 Abstract: In this work, a comparative study of the synthesis and magnetic properties of Fe3O4 nanoparticles obtained by the co-precipitation and hydrothermal methods with the adding of the sucrose as a chelating agent is reported. The analysis of transmission electron microscopy (TEM) show that particles are spherical-like with an average particle size ranging of 3

Agradecimentos: The authors thank Brazilian agencies FAPITEC(PRONEX), CAPES, CNPq (455608/2014-8, 455970/2014-9 and 152026/2016-9) for financial support. The authors also thank to the LNNano/CNPEM for technical support during electron microscopy experiments Abstract: In this work, we report on the anisotropic growth of alpha-Fe2O3 nanoslabs which are produced by co-precipitation method with the addition of sucrose. In our previous work, we have argued that such behavior can be related with the chelating agent. Experiments of X-ray diffraction (XRD), high-resolution transmission electronic microscopy (HRTEM) and magnetic measurements as a function of temperature and an applied magnetic field are used to characterize the samples. The HRTEM image of the sample prepared with 10 mmol/l of sucrose consists of faceted-like nanoslabs while that prepared without sucrose exhibits particles with a non-uniform shape. In this way, we can state that both the HRTEM images and the analysis of the XRD patterns show clearly a preferential growth of the [110] crystallographic direction. To strengthen our supposition, besides T- and field-dependence of magnetization are consistent with a superparamagnetic behavior the fit of the (Zero Field Cooling and Field Cooling) ZFC-FC curve for sample grown with 10 mmol/l of sucrose presents a strong increase of the effective anisotropy constant, K-eff, which can be related with the increasing of the shape magnetic anisotropy FUNDAÇÃO DE APOIO À PESQUISA E À INOVAÇÃO TECNOLÓGICA DO ESTADO DE SERGIPE - FAPITEC COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: We would like to thank S. M. Thomas for helpful discussions. The authors also thank Fapesp-SP (Grants 2012/04870-7, 2013/21457-9 2015/21290-2, 2015/21289-4, 2013/17427-7 and 2010/11949-3), CNPq and CAPES-Brazil for financial support and the Brazilian Nanotechnology National Laboratory (LNNANO) for providing the equipment and technical support for the experiments involving scanning electron microscopy (SEM - 20041) Abstract: Samples of nanostructured beta-Ga wires were synthesized by a novel method of metallic-flux nanonucleation. Several superconducting properties were observed, revealing the stabilization of a weak-coupling type-II-like superconductor (T-c approximate to 6.2 K) with a Ginzburg-Landau parameter kappa(GL) = 1.18. This contrasts the type-I superconductivity observed for the majority of Ga phases, including small spheres of beta-Ga with diameters near 15 mu m. Remarkably, our magnetization curves reveal a crossover field H-D, where we propose that the Abrikosov vortices are exactly touching their neighbors inside the Ga nanowires. A phenomenological model is proposed to explain this result by assuming that only a single row of vortices is allowed inside a nanowire under perpendicular applied field, with an appreciable depletion of Cooper pair density at the nanowire edges. These results are expected to shed light on the growing area of superconductivity in nanostructured materials FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES Aberto

Agradecimentos: The authors are grateful for accessing the facilities of National Synchrotron Light Laboratory (LNLS) and the financial support of the Brazilian agencies CAPES (Brazilian Federal Agency for the Support and Evaluation of Graduate Education) and CNPq (National Council for Scientific and Technological) Abstract: We report on thermogravimetric, structural and magnetization measurements in the YCrO3+gamma compound obtained by the co-precipitation method. The thermogravimentric analyses show that the weight losses which occur at three distinct steps are associated with water evaporation, formation of zircon-type YCrO4 compound and finally a phase transition from the tetragonal YCrO4 to the orthorhombic YCrO3. The X-ray diffraction measurements allied with the Rietveld refinement confirm such trend, that is, the observed Xray patterns are consistent with a gradual growth of zircon-type YCrO4 with tetragonal structure and space group 141/amd for annealing temperatures up to 600 degrees C followed by the phase transition to the orthorhombic YCrO3 phase with space group Pbnm for annealing temperatures above 625 degrees C. The X-ray absorption near edge structure (XANES) spectra carried out in the Cr K-edge reveal that the oxidation states of Cr ions depend on the synthesis temperature. The T-dependencies of magnetic susceptibility point out a ferromagnetic-antiferromagnetic transition as function synthesis temperature. The Curie and Neel temperatures are in agreement with that reported in literature for the YCrO4 and YCrO3 compounds, respectively. Besides, the MvsH curves measured at 2 and 50 K are consistent with the observed magnetic states to each sample COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Fechado

Agradecimentos: This work was supported by Brazilian funding agencies Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). The authors would like to acknowledge the Brazilian Nanotechnology National Laboratory (LNNANO) for providing the equipment and technical support for the experiments involving scanning electron microscopy and the Brazilian Synchrotron Light Laboratory (LNLS) for the beamtime (XRD1 16980) and the staff of the XDS Beamline for providing assistance during the experiment. We thank Anna Paula Sotero Levinsky, Junior Cintra Mauricio and Santiago J.A. Figueroa (LNLS) for help in the XAS measurements and data manipulation/analysis Abstract: This work reports on the dimensionality effects on the magnetic behavior of Fe3Ga4 compounds by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. Our results show that reducing the Fe3Ga4 dimensionality, via nanowire shape, intriguingly modifies its electronic structure. In particular, the bulk system exhibits two transitions, a ferromagnetic (FM) transition temperature at T-1 = 50 K and an antiferromagnetic (AFM) one at T-2 = 390 K. On the other hand, nanowires shift these transition temperatures, towards higher and lower temperature for T-1 and T-2, respectively. Moreover, the dimensionality reduction seems to also modify the microscopic nature of the T-1 transition. Instead of a FM to AFM transition, as observed in the 3D system, a transition from FM to ferrimagnetic (FERRI) or to coexistence of FM and AFM phases is found for the nanowires. Our results allowed us to propose the magnetic field-temperature phase diagram for Fe3Ga4 in both bulk and nanostructured forms. The interesting microscopic tuning of the magnetic interactions induced by dimensionality in Fe3Ga4 opens a new route to optimize the use of such materials in nanostructured devices FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ Aberto

Agradecimentos: This work was supported by the Brazilian funding agencies CNPq (National Council for Scientific and Technological), CAPES (Brazilian Federal Agency for the Support and Evaluation of Graduate Education) and FAPITEC-SE (Foundation for Support to Research and Technological Innovation of Sergipe State). The authors are grateful for access to the facilities of Brazilian Synchrotron Light Laboratory (LNLS) Abstract: In this work, we have carried out a detailed study of the magnetic and structural properties of YFe1-xCrxO3 (0

Agradecimentos: The authors also are grateful to the funding agencies FAPITEC-SE, FAPEMA and CNPq for financial support, The authors would also like to thank to the Brazilian Nanotechnology National Laboratory (LNNano/CNPEM, Brasil) for access to the HRTEM Abstract: We have studied the influence of chelating agents (glycerin and sucrose) on the structural and magnetic properties of cobalt ferrite (CoFe2O4) nanoparticles synthesized via co-precipitation method. The Rietveld refinements from X-ray diffraction patterns confirm that all samples are single phase identified in a cubic crystalline system belonging to the space group Fd-3m. Besides, we have verified that the addition of chelating agents produces a decreasing in the particles average size from 14(2) to 5(1) nm. Magnetization measurements as a function of temperature show a decrease in the blocking temperature (T-B) to sample obtained with addition of sucrose. A superparamagnetic behavior at room temperature was observed by magnetic measurements as function of field in the sample with 0.020 mol/L of sucrose. The results show that character chelating of sucrose reduces the coalescence effect and magnetic interaction in the CoFe2O4 nanoparticles. These results suggest that sucrose could be an alternative to control the structural and magnetic properties of other oxides nanoparticles FUNDAÇÃO DE APOIO À PESQUISA E À INOVAÇÃO TECNOLÓGICA DO ESTADO DE SERGIPE - FAPITEC FUNDAÇÃO DE AMPARO À PESQUISA E AO DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO DO MARANHÃO - FAPEMA FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP Fechado

Agradecimentos: This work was supported by FAPESP (in particular grants No 2006/60440-0, 2009/09247-3, 2010/11949-3, 2010/09545-1, 2011/12292-0, 2011/01564-0, 2011/23650-5, 2012/04870-7, 2013/17427-7), CNPq, FINEP-Brazil. The authors would like to acknowledge the Brazilian Nanotechnology National Laboratory (LNNano - Project Inspect-14958) for providing the equipment and technical support for the experiments involving scanning electron microscopy Abstract: Correlated electron intermetallic bulk systems exhibit exciting phenomena, such as unconventional superconductivity, heavy fermion behavior, magnetic ordering, and quantum criticality. However, such exciting properties in related systems with reduced dimensionality are rather unexplored and unpredictable. In this work, we explore the routes for synthesizing nanowires of the intermetallic antiferromagnet compound GdIn3 by an innovative method: the metallic-flux nanonucleation (MFNN). This technique allows the simultaneous synthesis of bulk GdIn3 single crystals (T-N(3D) = 45 K) and their low-dimensional (LD) analogs, which nucleate with diameter d approximate to 200 nm and length l approximate to 30 mu m inside pores of an Al2O3 template. Both systems were studied by means of Energy Dispersive Spectroscopy (EDS), magnetic susceptibility, heat capacity and electron spin resonance (ESR) measurements. Interestingly, the metallic nanowires show a drastic suppression of the antiferromagnetic ordering to T-N(LD) = 4 K. These observations suggest the presence of LD magnetic frustration in this compound and possibly open a new route to explore the role of low-dimensionality in strongly correlated materials FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO - FAPESP CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO - CNPQ FINANCIADORA DE ESTUDOS E PROJETOS - FINEP Fechado