Magnetic and Electronic Properties of Highly Mn-Doped β-NaGdF4 and β-NaEuF4 Nanoparticles with a Narrow Size Distribution

We have performed a detailed study of the magnetic and electronic properties of highly manganese-doped beta-NaGdF4 and beta-NaGdF4 nanoparticles with a narrow size distribution. XPS as well as XRF experiments confirm the successful doping of 11 +/- 2% Mn into beta-NaGdF4 and beta-NaGdF4 nanoparticles, i.e., a much higher Mn concentration than has been previously reported for the incorporation of bivalent transition metal ions into the beta phase of NaREF4 (RE = rare earth) nanocrystals. Owing to the high manganese concentration, we observed quenching of the Mn2+ emission in both materials and even quenching of the red Eu3+ emission in beta-NaGdF4 :11% Mn particles. We have investigated the Mn-Mn magnetic interactions by means of EPR spectroscopy, and SQUID magnetometry further supports a significant increase of the magnetization of the Mn-doped beta-NaGdF4 nanoparticles compared to pure beta-NaGdF4. By using element specific X-ray absorption spectroscopy and X-ray magnetic circular dichroism, we show that the magnetism of Mn-doped beta-NaGdF4 is dominated by the divalent Mn ions for Mn-doped beta-NaGdF4. A parallel alignment of the gadolinium and manganese magnetic moments is found.