Magnetic phase diagram of EuSySe1−y and EuSe under hydrostatic pressure

AC-susceptibility measurements of samples EuS_ySe_1?y and EuSe with applied hydrostatic pressure up to 15 kbar are reported and the magnetic phase diagrams of both systems are compared. Special attention is given to the range where the ferromagnetic and antiferromagnetic exchange interactions just compensate. Whereas in EuSe with applied pressure antiferromagnetic or ferromagnetic ordering is observed up to very close to the critical point J₁=-J₂, a spin glass phase occurs in EuS_ySe_1?y at the corresponding concentration.