Thermodynamic insights into the intricate magnetic phase diagram of EuAl4

The tetragonal intermetallic compound EuAl4 hosts an exciting variety of low-temperature phases. In addition to a charge density wave below 140 K, four ordered magnetic phases are observed below 15.4 K in zero field. Recently, a skyrmion phase was proposed based on Hall effect measurements under a c-axis magnetic field. We present a detailed investigation of the phase transitions in EuAl4 under c-axis magnetic field. Our dilatometry, heat-capacity, DC magnetometry, AC magnetic susceptibility, and resonant ultrasound spectroscopy measurements reveal three magnetic phase transitions not previously reported. The first key result is a detailed H parallel to [001] magnetic phase diagram mapping the seven phases we observe. Second, we identify a high-field phase, phase VII, which directly corresponds to the region were skyrmions have been previously suggested. Our results provide guidance for future studies exploring the complex magnetic interactions and spin structures in EuAl4.

Automated summary

The tetragonal intermetallic compound EuAl4 exhibits various low-temperature phases. This study investigates the phase transitions in EuAl4 under a c-axis magnetic field, revealing three previously unreported magnetic phase transitions and mapping a detailed magnetic phase diagram. The results provide guidance for exploring the magnetic interactions and spin structures in EuAl4.