Anisotropic paramagnetic response of hexagonal R MnO3

The anisotropic paramagnetic susceptibility of single crystals of the hexagonal manganites R MnO3 (R=Ho, Er, Tm, Yb, and Lu) is studied. It is found that the anisotropy of the paramagnetic Curie temperature along the sixfold axis and in the basal plane, θ - θ, is determined not by the anisotropic Mn-O-Mn interactions but rather by the quadrupolar charge distribution of the 4f shells of the rare-earth ions. These findings disclose the decisive role of the R ions in forming the paramagnetic behavior of R MnO3 and suggest a subtle interplay between the charge-density distribution of rare-earths and the symmetry of the spin-ordering of the Mn sublattices. © 2009 The American Physical Society.