Magnetic Properties of Heavy Rare Earths Diluted by Yttrium and Lutetium

A neutron-diffraction study of the heavy rare earths Tb, Dy, Ho, Er, and Tm diluted with yttrium and of Tb with lutetium is reported. The modulated antiferromagnetic structures of the rare-earth metals are found to exist in the alloys, but the ferromagnetic phases of Tb and Dy are destroyed with small admixtures of Y. The N\'eel temperatures of the alloys and the pure metals are found to be a universal function of the average of the square of the spin projection on $J$, given for these heavy-rare-earth alloys by $\ensuremath{\xi}=c{(g\ensuremath{-}1)}^{2}\ifmmode\times\else\texttimes\fi{}J(J+1)$, where $c$ is the atomic concentration of rare earth. The value of the interlayer angle $\ensuremath{\omega}$ at ${T}_{N}$ which is related to the wavelength of the modulation of the magnetic structure is also found to be a universal function of $\ensuremath{\xi}$, and the temperature variation of $\ensuremath{\omega}$ decreases with decreasing $\ensuremath{\xi}$ so that $\ensuremath{\omega}$ approaches a temperature-independent value of about 50\ifmmode^\circ\else\textdegree\fi{} per layer for small $\ensuremath{\xi}$, regardless of the magnetic ion in the alloy.