Magnetic properties of a layered and anisotropic rhombohedral compound: Bi2(1-x)Gd2xTe3.

Abstract

The paramagnetic resonance absorption spectra of ${\mathrm{Bi}}_{2(1\mathrm{\ensuremath{-}}\mathit{x})}$${\mathrm{Gd}}_{2\mathit{x}}$${\mathrm{Te}}_{3}$ grown by the Bridgman technique have been measured at room temperature. The magnetization measurements have been performed in magnetic-field intensities up to 65 kOe at temperatures of 1.8, 4.2, 16, and 25 K. The EPR data show that the ${\mathrm{Gd}}^{3+}$ site has a ${\mathit{C}}_{3\mathit{v}}$ symmetry, indicating a true substitution of ${\mathrm{Bi}}^{3+}$ atoms by ${\mathrm{Gd}}^{3+}$. The curve fitting of the magnetic-field dependence of the magnetization has been performed using a Brillouin function representing isolated magnetic ions. An extra term was introduced to represent the contribution of the pairs. The results indicate a weak antiferromagnetic coupling between the ${\mathrm{Gd}}^{3+}$ ions. This is similar to the one found in the case of ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$Te. The bond lengths as well as the bond angles in the case of ${\mathrm{Bi}}_{2(1\mathrm{\ensuremath{-}}\mathit{x})}$${\mathrm{Gd}}_{2\mathit{x}}$${\mathrm{Te}}_{3}$ and ${\mathrm{Pb}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Gd}}_{\mathit{x}}$Te are compared. The similarity of the ${\mathit{J}}_{\mathit{P}}$/${\mathit{k}}_{\mathit{B}}$ values (-0.5 K) in the two systems is explained in terms of superexchange interaction via anions between ${\mathrm{Gd}}^{3+}$.