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

Abstract

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.

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“…(2) Cr ions in the La dodecahedral site; both Cr and La ions have equivalent valence states, and the different ionic size may induce the disorder in the LGGO compound, which may generate a pronounceable weak crystal field in the dodecahedral site. 29 A similar mechanism and EPR spectrum are also reported by Kaczmarek et al 30 The simulated EPR spectra for the calculated SH parameters are marked as L1 and L2 in Figure 4. The symmetry of S−Cr and W−Cr is calculated as C 3 and low, axial C 4 , respectively.…”

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“…The fitting accurately reflects the EPR experimental spectrum over the entire measurement range. The above SH parameters are typical for Cr 3+ ions with S = 3/2. , It follows that the EPR signal originates from one type site of the isolated Cr 3+ ions in the octahedral crystal field. The values of SH parameters indicate the low symmetry of Cr 3+ ions and the high axial distortion of the Cr 3+ ion environment.…”

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“…The X-ray absorption near-edge structure results (Figure d) show the presence of Cr ions in the tetrahedral sites by the presence of the sharp peak at 5980 eV with a shoulder at 5996.2 eV, whereas the Cr 3+ ion in the octahedral site is confirmed by the peak at 6003.4 eV, similar to that of the standard Cr 2 O 3 . Electron paramagnetic resonance (EPR) at liquid nitrogen temperature (Figure e) is also conducted to obtain information on the local coordination symmetry and crystal field environment . The occurrence of a sharp EPR signal centered at g eff ≈ 2 arising from the isolated Cr 3+ ions ( S = 3/2) shifts to the lower magnetic field value of g eff ≈ 3.8 due to a large distortion in axial symmetry that affects the splitting of the EPR signal. − The La 3 Ga 4.95 GeO 14 :Cr 3+ powder sample exhibits three intense and several weak (up to six) lines while positioned at the chromium (Cr2) ion at the tetrahedral site in a weak crystal field.…”