In this dissertation we present the synthesis of magnetic nanoparticles of Mn1-xZnxCr2O4 e Cu1-xNixCr2O4 (0 x 1,0) compounds prepared by coprecipitation method. These compounds were characterized by X-ray diffraction and scanning electron microscopy measurement at room temperature. The CuCr2O4 and NiCr2O4 chromites, produced by solid state reaction method, were studied by ac susceptibility and magnetization as a function of temperature and magnetic field. The nanometric powders chromites have lattice parameters, which are consistent with those reported for the bulk materials in the literature. The average sizes of the particles were calculated from the Scherrer's equation and compared with the size obtained by scanning electron microscopy. We noticed an increase in the average size of particles with increasing temperature calcination. The variation of the lattice parameters in the Cu1-xNixCr2O4 system doped with Ni (0 ≤ x ≤ 1) allows identifying two regions, being a tetragonal and another cubic. The CuCr2O4 and the Cu1-xNixCr2O4 system display tetragonal symmetries, due to the Jahn-Teller effect in oxygen tetrahedral, however the cubic is NiCr2O4 at room temperature. The x-ray diffraction results in Mn1-xZnxCr2O4 system associated with Rieltveld refinement analyses, show that the samples with (0 ≤ x ≤ 1) have x-ray diffraction pattern similar (cubic symmetric and space group Fd3m), confirmed by Rietveld refinement, thus indicating that the main phase of the system as a whole remains unchanged with the replacement of Mn by Zn. Magnetic measurements were carried out with a SQUID magnetometer (Superconducting Quantum Interference Device) display a ferrimagnetic behavior for the CuCr2O4 bulk compound with a transition temperature TC = 122 K. The magnetic field dependence of the magnetization for the CuCr2O4 indicates an average magnetic of de 0.15 mB /per unit formula at 2 K which is smaller than the expected value for ferrimagnetic arrangement of Cr3+ and Cu2+ ions. We can explain the low value of saturate moment due to the triangular arrangement of spins. Cr3+ on the 001 planes are aligned parallel and opposite to Cr3+in adjacent planes yielding a net moment from the Cr3+ sublattices. The Cu2+ sublattice couples antiferromagnetically to the net moment of the Cr3+ sublattices creating a triangular configuration of spins. The coercive field at 2 K is approximately 2 kOe . Measurements of magnetization as a function of temperature for the NiCr2O4 show two magnet transitions in Tc = 75 k and Ts = 30 k, a related to a component ferrimagnetic (longitudinal) and another the antiferromagnetic component (transversal). From Magnetization versus field curves at 2 K we obtained the saturation magnetization 0.25 mB/ formula unit, less than the expected value of 1.2 mB/ formula unit. This decrease in magnetization at 2 K is due to the longitudinal component of the magnetic moment on the A site-(Ni2+) be larger than that of B site-(Cr3+). / Nesta dissertação apresenta-se a síntese das nanopartículas magnéticas dos sistemas Mn1-xZnxCr2O4 e Cu1-xNixCr2O4 (0 x 1,0) produzidas pelo método de coprecipitação. Estes compostos foram caracterizados por medida de difração de raios X e microscopia eletrônica de varredura à temperatura ambiente.As cromitas de CuCr2O4 e NiCr2O4, produzidas pelo método de reação de estado solido, tiveram suas propriedades magnéticas estudadas por magnetização e susceptibilidade ac em função da temperatura. As cromitas nanométricas apresentam parâmetros de rede, consistentes com os da forma bulk , reportados na literatura. Os tamanhos médios das partículas foram calculados a partir da equação de Scherrer e confrontados com o tamanho obtido por microscopia eletrônica de varredura. Percebemos um aumento no tamanho médio das partículas com o aumento da temperatura de calcinação. A variação dos parâmetros de rede do sistema Cu1-xNixCr2O4 dopado com Ni (0≤x≤1) permite identificar duas regiões de fases diferentes, a tetragonal e a cúbica. O CuCr2O4 e suas substituições por Ni apresentam simetrias tetragonais, devido ao efeito Jahn-Teller nos tetraedros de oxigênio, porém o NiCr2O4 é cúbico à temperatura ambiente. Os resultados de difração de raios X para o sistema Mn1-xZnxCr2O4 associados às análises de refinamento Rieltveld, mostram que as amostras com (0≤x≤1) possuem padrão de difração de raios-x similar (simetria cúbica e grupo espacial Fd3m), confirmadas por refinamento Rietveld, indicando assim que a fase principal para o sistema como um todo permanece inalterada com a substituição do Mn por Zn. Medidas magnéticas feitas com um magnetômetro SQUID (Superconducting Quantum Interference Device) exibem um comportamento ferrimagnético para o composto CuCr2O4 massivo com uma temperatura de transição TC= 122 K. A dependência da magnetização com o campo magnético para o CuCr2O4 indica um momento magnético de 0.15mB por fórmula unitária em 2K o qual é menor que o valor esperado do ordenamento ferrimagnético dos íons Cr3+ e Cu2+. Podemos explicar o baixo valor do momento de saturação devido ao arranjo triangular dos spins. Os Cr3+ no plano 001 são alinhados paralelos e opostos aos Cr3+ dos planos adjacentes produzindo um momento resultante de Cr3+ das subredes. A subrede do Cu2+ forma pares antiferromagneticamente com o momento da subrede Cr3+ criando uma configuração triangular dos spins. O campo coercivo é de aproximadamente 2 kOe. Medidas de magnetização em função da temperatura para o NiCr2O4 mostram duas transições magneticas em Tc = 75K e Ts = 30K, uma relacionada a uma componente ferrimagnético (longitudinal) e outra a componente antiferromagnética (transversal). Da dependência da magnetização (M) com o campo (H), obtivemos a magnetização de saturação de 0.25 mB/ fórmula unitária a 2K, valor menor do que o esperado 1.2 mB/ fórmula unitária. Esta diminuição na magnetização medida a 2K é devido a componente longitudinal do momento magnético no sítio-A (Ni2+) ser maior do que a do sítio-B (Cr3+).

In this work, we will focus on the quaternary system Cu1-xAgxInSe2 (CAIS) to investigate the effects of silver (Ag) contribution and exchange with copper (Cu) in CuInSe2. This system is located between the ternary semiconducting chalcopyrite compounds CuInSe2 and AgInSe2. These are two most popular materials applied in photovoltaic cells because of their high optical absorption coefficient, which is an important factor for the manufacture of devices, direct energy gap with values Eg ~1.05 and 1.24 eV, respectively, and excellent thermal stabilities in air. As being a quaternary alloy, we expect that Cu1-xAgxInSe2 will show the advantage of a large degree of variation of their properties as a function of the composition, which allows adjusting of the band gap and other properties. We will analyze the behavior of Ag in the structure depending on the annealing and the effects of the Ag exchange to the Cu vacancies in this crystal structure by changing x (Ag content). The crystals will be characterized structurally by X-ray diffraction (XRD). It will be used to prove crystallinity, determine perfection and lattice parameters depending on composition. Surface morphology and stoichiometry will be examined using scanning electron microscope (SEM) equipped with EDXA. Moreover, electrical properties including the temperature dependent electrical conductivity, and carrier concentrations and mobility extracted from Hall effect measurements, and, optical properties including absorption coefficient, photoconductivity, spectral transmission, and optical band gap have been determined to characterize Cu1-xAgxInSe2 thin films deposited using e-beam evaporation technique.