Incommensurate spin-density-wave antiferromagnetism in CeRu$_2$Al$_2$B

TL;DR

This paper uncovers an incommensurate spin-density wave phase in CeRu$_2$Al$_2$B, revealing complex magnetic behavior driven by competing interactions, and highlights its significance as a model for studying magnetic frustration in heavy-fermion systems.

Contribution

It provides the first detailed neutron diffraction evidence of an incommensurate SDW phase in CeRu$_2$Al$_2$B and explains its stabilization through a theoretical model.

Findings

Identification of a longitudinal incommensurate SDW between T_N and T_C.

Observation of a nearly temperature-independent propagation vector.

Discontinuous lock-in of the SDW wave vector at T_C.

Abstract

The newly discovered Ising-type ferromagnet CeRu$_2$Al$_2$B exhibits an additional phase transition at $T_\textrm{N}$ = 14.2 K before entering the ferromagnetic ground state at $T_\textrm{C}$ = 12.8 K. We clarify the nature of this transition through high resolution neutron diffraction measurements. The data reveal the presence of a longitudinal incommensurate spin-density wave (SDW) in the temperature range of $T_\textrm{C}<T<T_\textrm{N}$. The propagation vector ${\bf q} \sim (0,0,0.148)$ is nearly temperature independent in this region and discontinuously locks into ${\bf q} = 0$ at $T_\textrm{C}$. Mean-field calculations of an effective Ising model indicate that the modulated SDW phase is stabilized by a strong competition between ferromagnetic and antiferromagnetic exchange interactions. This makes CeRu$_2$Al$_2$B a particularly attractive model system to study the global phase diagram of ferromagnetic heavy-fermion metals under influence of magnetic frustration.