Negative thermal expansion in spiral magnetic Lu2Fe16.5Ru0.5

Negative thermal expansion (NTE) has been a topic of interest for magnetic metals due to its potential for applications. Knowledge of the relationship between magnetism and the NTE can be conducive facilitate the exploration of both new magnetic functions and NTE systems. In this work, we apply neutron diffraction on a spiral magnetic Lu2Fe16.5Ru0.5 (space group: P63/mmc) to study the evolution of magnetic structure and thermal expansion under various magnetic fields. Strong negative thermal expansion emerges along the c axis over magnetic ordering temperature range from 10 to 200 K, yet normal positive thermal expansion is observed within basal plane, thus yielding a volumetric low thermal expansion (αv = +2.9 × 10−6 K−1, 10–200 K). Moreover, a high magnetic field of 2 Tesla is found to suppress the interplanar spiral magnetic ordering but have weak impact on NTE. These findings imply magnetic disorder may be more essential than the change of magnetic texture for inducing a thermal expansion anomaly in such NTE systems.