Magnetization studies ofRMn6Ge6−xGaxsingle crystals (R=Sc,Y, Gd–Lu;0.63⩽x⩽1.00)

Abstract

The magnetic properties of single crystals of rare-earth compounds of composition $R{\mathrm{Mn}}_{6}{\mathrm{Ge}}_{6\ensuremath{-}x}{\mathrm{Ga}}_{x}$ $(x\ensuremath{\approx}1)$ have been studied. In these compounds, the Mn sublattice orders ferromagnetically with a preferred moment direction perpendicular to the $c$ axis. In the compounds in which also the $R$ component carries a magnetic moment, the latter couple antiparallel to the Mn moments. Upon cooling from room temperature to cryogenic temperatures, the $R$-sublattice anisotropy becomes the dominant contribution to the total magnetocrystalline anisotropy, which leads to a spin-reorientation transition at intermediate temperatures for $R=\mathrm{Tb}\ensuremath{-}\mathrm{Yb}$. At low temperatures, the preferred moment directions are characterized by an easy axis for $R=\mathrm{Tb}$, Er, Tm, and Yb and by an easy cone for $R=\mathrm{Dy}$ and Ho. A satisfactory account of the observed preferred moment directions has been given in terms of crystal-field theory. Measurements of the magnetization in the main crystallographic directions have been made in high magnetic fields, up to about 55 T. The interplay between the antiferromagnetic intersublattice $R$-Mn coupling and the magnetocrystalline anisotropy leads to field-induced magnetic phase transitions which are particularly pronounced in the compounds with Ho, Er and Tm.