High-field ESR and magnetization study of [Cu(pyz)₂(HF₂)]PF₆: an S = 1/2 quasi-two-dimensional Heisenberg magnet

Electron spin resonance and magnetization studies of the quasi-two-dimensional spin system [Cu(pyz)₂(HF₂)]PF₆ have been performed in static and pulsed magnetic fields up to 50 T. It is argued that the magnetization is governed by the two-dimensional nature of spin correlations due to the large anisotropy of the exchange couplings (J_perp/J = 0.01, where J is the in-plane and J_perp is the interlayer exchange parameters). The magnetization saturates at the critical fields 37.1 T and 34.3 T for magnetic field applied perpendicular and parallel to the direction, respectively. The frequency-field diagram of the magnetic excitations changes dramatically below the Néel temperature (T_N = 4.38 K). Our observation reveals an easy-plane type of the magnetic anisotropy. The exchange field (H_E = 18.5 T) and out-of-plane anisotropy field (H_A = 0.05 T) were calculated using a mean-field-theory approximation.