Impacts of pressure to the structural, electronic and magnetic properties of Dirac semimetal EuMnBi 2

We report our investigations on the effects of pressure on the electronic and magnetic properties of magnetic Dirac semimetal ${\mathrm{EuMnBi}}_{2}$ by using electrical transport, synchrotron x-ray diffraction, and x-ray absorption spectroscopy. The antiferromagnetic interaction due to the Eu magnetic moment in ${\mathrm{EuMnBi}}_{2}$ is enhanced under pressure up to $\ensuremath{\sim}3.9\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$. The N\'eel temperature (${T}_{N}$) is found to disappear above 4 GPa and a new transition ${T}_{t}$ at around 29 K emerges above 6 GPa. ${T}_{t}$ remains relatively constant up to 15 GPa, above which it increases with further compression, reaching $\ensuremath{\sim}60\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ at 22 GPa. Eu $L$-edge x-ray absorption spectroscopy revealed a valence change of Eu toward a trivalent state that begins above 6 GPa, which indicates that ${T}_{t}$ is likely related to the valence transition temperature of Eu. Sign reversal of the Hall resistivity above 7 GPa suggests that the valence change of Eu also induces a Fermi surface modification.