Single crystals have been prepared of rare earth hexagonal solid solutions having 4f electron concentrations (10 to 11) near which the Stevens' factors change sign. Compositions are Ho3Er, HoEr, HoEr3, DyEr, and DyEr3. Moment measurements have been made on spheres in the a, b, and c directions (a⊥b⊥c) at 4.2°in fields to 140 kOe. From the data can be derived the cone angles in the ferromagnetic structures, the break-down of the cone structure (when H ⊥ c), the approach to saturation against anisotropy forces, and the field strengths at which fanning occurs when H ∥ a or ∥ b. The cone angles so determined are a linear function of the 4f electron concentration, in agreement with neutron-diffraction data. In Ho3Er the b direction is the easiest in the ab plane, as in Ho, whereas in HoEr and HoEr3 a is easier than b. When H ⊥ c in Ho3Er, the moment approaches saturation smoothly against anisotropy forces, whereas in others fanning occurs in a more complicated manner. © 1968 The American Institute of Physics.