O objetivo principal deste trabalho é o estudo por ressonância paramagnética eletrônica das impurezas Cr³⁺, Er³⁺ e Mn³⁺ no monocristal Ca₃Ga₂Ge₃O₁₂ (denominado CGGG) nas freqüências de 1.3, 10 e 34 GHz e nas temperaturas de 4,2K a 300K. O Hamiltoniano de spin para o Cr³⁺ alojado no sítio octaédrico com simetria C Cr_3i é dado por: H = β[g_⊥ (H_xS_x + H_yS_y) + g_‌H_zS_z] + D (S²_z - 1/3 S (S+1). Os parâmetros do Hamiltoniano de spin para o íon Cr³⁺ em baixas concentrações são: g_‌ = 1,9727 ± 0,0003, g_⊥ = 1,9617 ± 0,0008 e D = 16,20 ± 0,02GHz para CGGG dopados com o íon Cr³⁺. Os cristais CGGG, dopados com Er³⁺ e Cr³⁺, apresentaram os seguintes parâmetros g_‌ = 1,9662 ± 0,0003, g_⊥ = 1,9617 ± 0,0008 e D = 15,82 ± 0,02GHz. Os parâmetros do Hamiltoniano de spin efetivo para o íon Er³⁺ alojado no sítio dodecaédrico e com simetria D₂ são: g_x = 2,690 ± 0,0005, g_y = 4,095 ± 0,005 e g_z = 5,082 ± 0,005. Os centros paramagnéticos Mn²⁺ produzidos em cristais dopados com Cr³⁺, irradiados com raios X, à temperatura ambiente, apresentam o fator-g isotrópico, g = 2,0066 ± 0,0001 e a constante de interação hiperfina A = 90 Gauss. Medimos, também as dependências das larguras de linhas com a temperatura, nas três bandas e para banda X medimos nas temperaturas de 4,2K até 300K

In this work was studied the Electron Paramagnetic Resonance (RPE) of the impurities Cr³⁺, Er³⁺ and Mn³⁺ in Ca₃Ga₂Ge₃O₁₂ single crystals (Known as CGGG) at frequencies of 1.3, 10 and 34 GHz in the temperatures range 4,2K to 300K. Spin Hamiltonian for the Cr³⁺ íons, located at octahedric position with symetry Cr_3i is given by: H = β[g_⊥ (H_xS_x + H_yS_y) + g_‌H_zS_z] + D (S²_z - 1/3 S (S+1). The relevant parameters for CGGG lightly dopped with Cr³⁺ as determined from the EPR spectra are: g_‌ = 1,9662 ± 0,0003, g_⊥ = 1,9617 ± 0,0008 and D = 15,82 ± 0,02GHz. CGGG crystals simultaneously dopped with Er³⁺ and Cr³⁺ shown the following parameters: g_‌ = 1,9662 ± 0,0003, g_⊥ = 1,9617 ± 0,0008 e D = 15,82 ± 0,02GHz. Effective spin Hamiltonian parameters for Er³⁺ íon, located at dodecahedric position and with symetry D², are: g_x = 2,690 ± 0,0005, g_y = 4,095 ± 0,005 e g_z = 5,082 ± 0,005. Paramagnetic centers Mn²⁺ produced in Cr³⁺ dopped crystals, X-ray irradiated, at room temperature, shown the isotropic g-factor g = 2,0066 ± 0,0001 and the hyperfine interaction constant A = 90 Gauss. Also, was measured the temperature dependence of the line width in the three frequency bands, in the range of liquid nitrogen to room temperature. In the case of the X-band, the measurements were extended to lower temperatures, 4.2K to 300K