The compound Pb₂VO(PO₄)₂ belongs to the family of vanadyl phosphates and hosts magnetically almost isolated layers of V⁴⁺ ions which carry a spin S=½. The spins Hamiltonian approximates a square lattice with ferromagnetic nearest and anti ferromagnetic next nearest couplings. A previous neutron study has found that the antiferromagnetic ground state is less frustrated than thermodynamic measurements had initially suggested [1]. It is therefore rather surprisingly that for fields along the magnetic anisotropy axis, a new magnetic state emerges through a discontinuous transition and persists in a narrow field range just below saturation. In this talk the full H-T phase diagram, determined by means of magnetization, torque, NMR and high field neutron diffraction experiments, are presented and properties of the presaturation phase are discussed [2].

[1] S. Bettler et al, Phys. Rev. B 99, 184437 (2019)
[2] F. Landolt et al, Phys. Rev. B 102, 094414 (2020).