Magnetic properties of Tb--Ho single crystal alloys. III. Neutron diffraction studies of Ho rich alloys

Neutron diffraction studies on several polycrystal and single crystal samples of Ho rich Tb–Ho alloys are reported. Polycrystalline samples containing 90%, 92%, 94%, 96%, and 98% Ho, as well as pure Ho, were studied at room temperature and at 8°K as a preliminary investigation for subsequent single crystal work. Three single crystal samples containing 93%, 95%, and 98% Ho were studied in detail from room temperature to 4.2°K. Both the Curie and Néel temperatures of the single crystal alloys were found to decrease almost linearly as the Ho concentration was increased. Both the 93% and 95% Ho alloys were found to have ordered phases similar to that of the 90% Ho alloy, with the exception that fifth and seventh harmonics caused by the distortion of the simple helical arrangement were observed for 95% Ho between 40°K and the Curie temperature at about 15°K. We find that the magnetic structure of the 98% Ho alloy corresponds to a magnetic structure on the borderline between that of pure Ho and that of 90% Ho. It shows all the characteristic features observed for pure Ho with the important exception that it does not transform to the conical spiral structure. Rather, the moments are still confined to the basal plane, most of them in the distorted helical arrangement bunched around the easy b direction, with some 4.4% of them collapsed into ferromagnetic ordering along the b direction.