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Crystal-structure studies on Tm2Fe17-xGax (x = O, 1, 2, 3, 4, 5, 6, 7, and 8) compounds have shown that the prepared samples are single phase with the 2:17-type structure. Both the unit-cell volume and the saturation magnetization at 1.5 K decrease linearly with increasing Ga content. The Curie temperature is found to increase with increasing x; it goes through a maximum value of 485 K at about x = 3 to lower values and then it rises again. The Tm2Fe17-xGax compounds exhibit a spin-reorientaiton transition at low temperature. X-ray diffraction measurements on magnetically aligned Tm2Fe17-xGax powders show that the compounds with x less than or equal to 6 have the easy-plane type of magnetic anisotropy, whereas the compounds with x less than or equal to 7 exhibit the easy c-axis type of magnetic anisotropy at room temperature. (C) 1997 American Institute of Physics.