Competing magnetic structures and magnetic transitions inEr2Ni2Pb: Powder neutron diffraction measurements

Abstract

We have studied the magnetic structures of ${\text{Er}}_{2}{\text{Ni}}_{2}\text{Pb}$ using a powder neutron diffraction technique in zero field. Previous bulk measurements suggested three distinct magnetic phase transitions. Our neutron diffraction experiments, which were made in the range 1.5\ensuremath{-}5 K, showed that magnetic Bragg reflections in ${\text{Er}}_{2}{\text{Ni}}_{2}\text{Pb}$ can be indexed by several propagation vectors that coexist over an extensive temperature range. Rather than a homogeneous magnetic structure that is simultaneously described by all the existing propagation vectors, several spatially separated structures appear to exist in ${\text{Er}}_{2}{\text{Ni}}_{2}\text{Pb}$. The appearance/disappearance of representative reflections at ${T}_{N}=3.5\text{ }\text{K}$, ${T}_{m1}=3.0\text{ }\text{K}$, ${T}_{m2}=2.3\text{ }\text{K}$, and ${T}_{m3}=1.8\text{ }\text{K}$ denote magnetic phase transitions. The only magnetic state that is determined by a single propagation vector exists just below ${T}_{N}$. In all other magnetic states, more than one propagation vectors are stable. Except for the lowest temperature state, which is commensurate, all other propagation vectors are incommensurate with respect to the crystal structure. Although the coexistence of several spatially separated magnetic structures can be explained by the competition of magnetic interactions along particular crystallographic directions, some of the details, e.g., the exact ground-state magnetic structure, are still unclear and need further study.