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The crystal structures of Nd(4)Ga(2)O(9) and Sm(4)Ga(2)O(9) compounds synthesized by solid-state reaction at 1400degreesC are investigated. X-ray diffraction shows that Nd(4)Ga(2)O(9) and Sm(4)Ga(2)O(9) are monoclinic system with the space group P2(1)/c, and lattice parameters a = 7.7656(1) Angstrom, b = 10.9689(1) Angstrom, c = 11.4727(1) Angstrom, beta = 109.06(1)degrees for Nd(4)Ga(2)O(9), and a = 7.6613(1) Angstrom, b = 10.8546(1) Angstrom, c = 11.4080(1) Angstrom, beta = 108.80(1)degrees for Sm(4)Ga(2)O(9). The gallium atoms are in the center of distorted oxygen tetrahedra with an average Ga-O bond distance between 1.82 and 1.85 Angstrom. The rare earth atoms are sixfold or sevenfold coordinated by oxygen. The oxygen atoms are threefold and fourfold coordinated. The magnetization for these compounds clearly reflects paramagnetism. The magnetic susceptibility chi changes with temperature in a Curie-type manner. (C) 2004 Elsevier B.V All rights reserved.