Pressure dependence of ferromagnetic phase boundary in BaVSe3 studied with high-pressure μ+SR

The magnetic nature of a quasi-one-dimensional compound, ${\mathrm{BaVSe}}₃$, has been investigated with positive muon spin rotation and relaxation (${\ensuremath{\mu}}⁺\mathrm{SR}$) measurements at ambient and high pressures. At ambient pressure, the ${\ensuremath{\mu}}⁺\mathrm{SR}$ spectrum recorded under zero external magnetic field exhibited a clear oscillation below the Curie temperature (${T}_C\ensuremath{\sim}41\phantom{\rule{0.16em}{0ex}}\mathrm{K}$) due to the formation of quasistatic ferromagnetic order. The oscillation consisted of two different muon spin precession signals, indicating the presence of two magnetically different muon sites in the lattice. However, the two precession frequencies, which correspond to the internal magnetic fields at the two muon sites, could not be adequately explained with relatively simple ferromagnetic structures using the muon sites predicted by density functional theory calculations. The detailed analysis of the internal magnetic field suggested that the V moments align ferromagnetically along the $c$ axis but slightly canted toward the $a$ axis by ${28}^{\ensuremath{\circ}}$ that is coupled antiferromagnetically. The ordered V moment (${\mathbit{M}}_{\mathrm{V}}$) is estimated as (0.59, 0, 1.11) ${\ensuremath{\mu}}_{\mathrm{B}}$. As pressure increased from ambient pressure, ${T}_C$ was found to decrease slightly up to about 1.5 GPa, at which point ${T}_C$ started to increase rapidly with the further increase of the pressure. Based on a strong ferromagnetic interaction along the $c$ axis, the high-pressure ${\ensuremath{\mu}}⁺\mathrm{SR}$ result revealed that there are two magnetic interactions in the $ab$ plane; one is an antiferromagnetic interaction that is enhanced with pressure, mainly at pressures below 1.5 GPa, while the other is a ferromagnetic interaction that becomes predominant at pressures above 1.5 GPa.