Single-crystal neutron diffraction studies on CeCu2 Ge2sand CeCu1.9 Ni0.1 Ge2s

Abstract

We have performed single-crystal neutron diffraction studies on ${\mathrm{CeCu}}_2$ ${\mathrm{Ge}}_2$ and ${\mathrm{CeCu}}_{1.9}$ ${\mathrm{Ni}}_{0.1}$ ${\mathrm{Ge}}_2$ to get insight into the very unusual magnetic properties of these compounds. ${\mathrm{CeCu}}_2$ ${\mathrm{Ge}}_2$ orders antiferromagnetically below ${\mathrm{T}}_{\mathrm{N}}$ =4.15 K in an incommensurate sinusoidal amplitude modulated structure. ${\mathrm{CeCu}}_{1.9}$ ${\mathrm{Ni}}_{0.1}$ ${\mathrm{Ge}}_2$ shows two successive magnetic phase transitions at ${\mathrm{T}}_{\mathrm{N}1\mathrm{}}$ =3.65 K and ${\mathrm{T}}_{\mathrm{N}2\mathrm{}}$ =2.65 K, respectively. The corresponding magnetic structures are very similar to each other as well as to the magnetic structure of pure ${\mathrm{CeCu}}_2$ ${\mathrm{Ge}}_2$ . Based on the temperature dependence of the intensities of the principal magnetic reflections, the two magnetic phases seem to superimpose independently of each other.