Alloys of the title formula are studied by powder X-ray and neutron di
ffraction, magnetic susceptibility and magnetization in fields up to 8
T. The Curie temperature has a maximum for x=7. For x < 3 the anisotr
opy is conical at room temperature. At lower temperatures a spin reori
entation to planar and at higher temperatures to axial alignment takes
place. For x greater-than-or-equal-to 5 the anisotroples are axial fo
r all the alloys and temperatures. A phase diagram is proposed.