Enhanced Néel-Type Skyrmion Stability in Polar VOSe₂O₅ through Tunable Magnetic Anisotropy under Pressure

Polar VOSe₂O₅, with P4cc space group (C_4V symmetry), was recently identified as hosting a rare Néel-type skyrmion phase within a very narrow range of temperature and magnetic field. Motivated by this discovery, we investigated the effect of pressure on its magnetic properties, focusing on improving the stability of the skyrmion phase. At ambient pressure, two magnetic transitions were observed at T_C1 ~ 7.4 K and T_C2 ~ 4.0 K. Notably, the contrasting behavior of these transitions under applied magnetic fields—T_C1 increases while T_C2 is suppressed—reflects the magnetic anisotropy in VOSe₂O₅. Neutron diffraction refinements reveal a three-up-one-down spin configuration, with alignment switching from the c-axis at 6.0 K to the b-axis at 1.8 K, further demonstrating the anisotropic nature. Pressure-dependent AC susceptibility measurements show T_C1 increasing by 0.043(3) K/kbar and T_C2 decreasing by -0.052(4) K/bar, indicating pressure-tunable anisotropy. The field-temperature (H-T) phase diagrams confirm the significant stabilization of the Néel-type skyrmion phase under 14.21 kbar of pressure, with its area expanding approximately threefold. These findings underscore the role of pressure in promoting Néel-type skyrmion stability through modulation of magnetic anisotropy, offering valuable insights into controllable topological phases for spintronics and related technological applications.