Absolute measurement of the ordered magnetic moment in holmium-rich (Er1-xHox)Rh4B4

Powder neutron diffraction measurements have been performed on ferromagnetic (Er1-xHox)Rh4B4 for concentrations x=1.0, 0.89, 0.84, and 0.75 to determine the ordered magnetic moment and form factor for holmium. The magnetic scattering intensities have been put on an absolute basis by comparison with pure copper-powder Bragg peaks in order to avoid systematic errors that might be associated with the evaluation of the nuclear structure factors of the samples themselves. For HoRh4B4 the saturated magnetic moment was determined to be z=(8.610.06)B, which is in good agreement with our previous determination. The measurements on the alloys gave the same holmium moment within experimental error. This value is considerably smaller than the prediction of 10B based on a single-ion crystal-field model. The magnetic form factor for the pure holmium compound has also been determined as a function of sin(theta)/, and is found to be in good agreement with the calculated form factor for Ho3+. Thus any rhodium moment which contributes to the ferromagnetic component of the magnetization must be less than 0.07B.