Magnetic properties of GdMn xFe1_xSi (x = 1, 0.9, 0.8, 0.7, 0.6, 0) compounds were investigated. Both GdMnSi and GdFeSi crystallize in the CeFeSi-type tetragonal structure and form a complete solid solution without any change in the crystal structure. Magnetic measurements were made in static magnetic fields up to 1 MA/m in the temperature range from 77 K to 420 K. For GdFeSi these measurements were carried out on single crystal sample. It was found that the increase in Fe content leads to a

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... rp decrease in saturation magnetic moment. The Curie temperature increases in the concentration range 0.7 < x < 1 and monotonously decreases for x < 0.6. These effects could be explained by strong dependence of the exchange integrals on the interatomic distances. PACS numbers: 75.20.En