Use of Stevens coefficients for the prediction of magnetic transitions in pseudobinaryR1−xRx'Al2alloys: Application to Tm1−xTbxAl2

Abstract

Recent heat-capacity and low-field magnetic susceptibility measurements revealed unusual magnetic phenomena occurring in Er${}_{1\ensuremath{-}x}$$R$${}_{x}$Al${}_{2}$ systems (where $R$ $=$ Dy,Tb) in the vicinity of a ``magic'' concentration of $x$ $=$ 0.25. Empirically, such behavior was attributed to different shapes of the 4f charge densities of the ${R}^{3+}$ ions, which are represented by the opposite signs of the second-order Stevens factors. Here we show that by using both the signs and magnitudes of the second- order Stevens factors, magnetic transitions can be predicted in a broader range of pseudobinary ${R}_{1\ensuremath{-}x}{R}_{x}^{'}$Al${}_{2}$ alloys, where $R$ and $R$\ensuremath{'} are rare-earth metals that have opposite signs of second-order Stevens factors. The predictions have been verified using the Tm${}_{1\ensuremath{-}x}$Tb${}_{x}$Al${}_{2}$ system as a model using x-ray diffraction, magnetic susceptibility, and heat-capacity measurements. First-principles calculations have also been performed to explore the behavior of the density of states near the Fermi level.