EPR NMR, and XPS study of LaAlO3 phase transition with enhanced magnetic and Faraday rotation properties in glass-ceramics

Abstract

The phase transition of LaAlO3 in heavy metal oxide lead-tellurite glass was obtained and verified, along with its influence on glass structure, magnetic, and Faraday rotation properties were characterized through various techniques such as nuclear magnetic resonance (NMR), X-ray neutron diffraction, transmission electron microscopy, X-ray photoelectron microscopy, vibrating-sample magnetometer, and electron paramagnetic resonance (EPR). Cubic LaAlO3 nanocrystals were synthesized by one-pot hydrothermal technique and doped at 1, 5, 10, and 15 mol% into glasses, respectively. The LaAlO3 nanocrystals in as-casted glasses were characterized to be around 17 nm in cubic phase belonging to the Pm3m space group. After crystallization treatment at 360 °C for 2 h, cubic LaAlO3 phases were changed to 14–27 nm-rhombohedral phases due to the temperature-induced viscosity and strain in the melt. The phase transition yielded great modification to the glass structure through converting TeO4→TeO3, AlO6→AlO4, BO4→BO3, and producing non-bridging oxygen. The LaAlO3 doping enhanced the diamagnetism of as-casted glasses, but after phase transition, the weak diamagnetic nature was changed to strong ferromagnetism and the magnetization significantly increased with the LaAlO3 doping amount (Ms =55 emu/g). The mechanism behind magnetic property enhancement was discussed through 27Al NMR and EPR of glasses. The Verdet constant of glass with 10% LaAlO3 was greatly improved to 175 rad/ T.m at 633 nm which is much higher than the documented values in the literature.