Perturbation-tuned triple spiral metamagnetism and tricritical point in kagome metal ErMn₆Sn₆

Kagome materials are of topical interest for their diverse quantum properties linked with correlated magnetism and topology. Here, we report anomalous hydrostatic pressure (p) effect on ErMn₆Sn₆ through isobaric and isothermal-isobaric magnetization measurements. Magnetic field (H) suppresses antiferromagnetic T_N while simultaneously enhancing the ferrimagnetic T_C by exhibiting dual metamagnetic transitions, arising from the triple-spiral-nature of Er and Mn spins. Counter-intuitively, pressure enhances both T_C and T_N with a growth rate of 74.4 K GPa⁻¹ and 14.4 K GPa⁻¹ respectively. Pressure unifies the dual metamagnetic transitions as illustrated through p-H phase diagrams at 140 and 200 K. Temperature-field-pressure (T-H, T-p) phase diagrams illustrate distinct field- and pressure-induced critical points at (T_cr = 246 K, H_cr = 23.3 kOe) and (T_cr = 435.8 K, p_cr = 4.74 GPa) respectively. An unusual increase of magnetic entropy by pressure around T_cr and a putative pressure-induced tricritical point pave a unique way of tuning the magnetic properties of kagome magnets through simultaneous application of H and p.