Doping effects of hexagonal manganitesEr1−xYxMnO3with triangular spin structure

Abstract

We have studied doping effects of hexagonal manganites ${\mathrm{Er}}_{1\ensuremath{-}x}{\mathrm{Y}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$, which are found to have 2D triangular spin structure for all the samples studied here. Upon doping Er at the Y site, the magnetic structure changes gradually from the ${\ensuremath{\Gamma}}_{1}$ representation of $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ to the ${\ensuremath{\Gamma}}_{2}$ representation of $\mathrm{Er}\mathrm{Mn}{\mathrm{O}}_{3}$ while the ordered moment remains almost unchanged in magnitude over the whole doping range. Despite the gradual change in the magnetic structure with doping, geometrical frustration effects expected of the 2D triangular spin structure with antiferromagnetic interaction between nearest neighbors show very strong doping dependence. For example, although $\mathrm{Y}\mathrm{Mn}{\mathrm{O}}_{3}$ shows all the signs of Mn moments being geometrically frustrated in the susceptibility and neutron diffraction data, such evidence of frustration effects is nearly absent in $\mathrm{Er}\mathrm{Mn}{\mathrm{O}}_{3}$. We suggest that magnetic coupling along the $c$ axis between Er and Mn moments should be responsible for the drastic doping dependence of the geometrical frustration effects.