Ultralow blocking temperature and breakdown of the giant spin model in Er 3 + -doped nanoparticles

摘要: The magnetization of luminescent ${\text{Er}}^{3+}$-doped ${\text{PbF}}_{2}$ nanoparticles (formula ${\text{Er}}_{0.3}{\text{Pb}}_{0.7}{\text{F}}_{2.3}$) has been studied. Despite the high concentration doping ${\text{Er}}^{3+}$ ions and relatively large size (8 nm) these we have found no deviation between field-cooled zero-field-cooled curves down to $T=0.35\text{ }\text{K}$, which points out an ultralow blocking temperature for reversal magnetization. We also strongly deviating $M(H/T)$ different temperatures $T$. These results altogether show that investigated are not superparamagnetic, but rather each ion in is a paramagnetic state very low temperatures, implies breakdown N\'eel-Brown giant spin model case nanoparticles. Calculations within noninteracting completely support this conclusion. Due temperature, potential magnetic field-induced nanoscale refrigeration with option their optical localization control.