Magnetic characterization of microcrystalline Na₃Ln_0.99–xEr_0.01Cr_x(PO₄)₂ orthophosphates synthesized by Pechini method (Ln = La, Gd)

Na₃Ln(PO₄)₂ orthophosphates (Ln = La, Gd) doped with Er³⁺ and co-doped with Cr³⁺ ions were synthesized by Pechini method and characterized by electron paramagnetic resonance (EPR) and magnetic susceptibility measurements. Low temperature EPR spectra were detected and analyzed in terms of temperature dependence and the structure of the obtained materials. They show that erbium and chromium ions substitute Ln³⁺ and also Na⁺ ions or Na⁺ channels forming complex EPR spectra. Both kinds of ions reveal ferromagnetic type of interaction which shows some anomaly at the temperature between 10 K and 15 K. Magnetic susceptibility reveals a weak antiferromagnetic kind of interaction dominating in the whole temperature range, from 3.5 to 300 K.