Ruddlesden-Popper Oxyfluorides La 2 Ni 1- x Cu x O 3 F 2 (0 ≤ x ≤ 1): Impact of the Ni/Cu Ratio on the Thermal Stability and Magnetic Properties.

Ruddlesden-Popper oxyfluorides of the substitution series La 2 Ni 1- x Cu x O 3 F 2 (0 ≤ x ≤ 1) were obtained by topochemical fluorination with polyvinylidene fluoride (PVDF) of oxide precursors La 2 Ni 1- x Cu x O 4 . The thermal stability and the temperature-dependent unit cell evolution of the oxyfluorides were investigated by high-temperature XRD measurements. The oxyfluoride with x = 0.6 shows the highest decomposition temperature of θ dec ∼ 520 °C, which is significantly higher than the ones found for the end members La 2 NiO 3 F 2 ( x = 0) θ dec ∼ 460 °C and La 2 CuO 3 F 2 ( x = 1) θ dec ∼ 430 °C. The magnetic properties of all La 2 Ni 1- x Cu x O 3 F 2 oxyfluorides were characterized by field- and temperature-dependent measurements as well as DFT calculations of the magnetic ground state. An antiferromagnetic ordering was derived for all substitution levels. For the Néel temperature ( T N ), a nonlinear dependence on the copper content was found, and comparably high values of T N in the region of 200-250 K were observed in the broad composition range of 0.3 ≤ x ≤ 0.8.