Phase diagram and spin waves in the frustrated ferro-antiferromagnet SrZnVO(PO4)2

Single crystals of the frustrated S=1/2 ferro-antiferromagnetic proximate square lattice material SrZnZnVO(PO$_4$)$_2$ are studied in magnetometric, calorimetric, neutron diffraction and inelastic neutron scattering experiments. The measured spin wave spectrum reveals a substantial degree of magnetic frustration and a large quantum renormalization of the exchange constants. The H-T magnetic phase diagram is established. It features a novel pre-saturation phase, which appears for only one particular field orientation. The results are discussed noting the similarities and differences with the previously studied and similarly structured Pb$_2$VO(PO$_4$)$_2$ compound.