Effects of induced optical tunable and ferromagnetic behaviors of Ba doped nanocrystalline LaB6

Abstract

Multiple nanocrystalline rare-earth hexaborides La_1−xBa_xB₆ have been synthesized via a single step solid-state reaction. The Ba doping effects on crystal structure, grain morphology, magnetic and optical absorption properties were investigated using XRD, FESEM, HRTEM, SQUID magnetometry and optical measurements. The results show that all the Ba-doped hexaborides crystallize in the CsCl-type single phase, indicating the Ba atoms occupied the lattice sites of LaB₆. The optical absorption results indicate that the absorption valleys of LaB₆ are red-shifted from 622 nm to 780 nm when the Ba doping content increases to x = 0.8. The first-principle calculation results reveal that Ba doping reduces the total kinetic energy of the electrons of LaB₆, which lead to the absorption valleys moving toward a higher wavelength. Meanwhile, the band gap of BaB₆ obtained from optical absorption is in good agreement with the theoretical calculation results. The magnetic measurements results showed that Ba doping lead to room-temperature ferromagnetism of LaB₆ due to the different ionic radii of La³⁺ and Ba²⁺ causing intrinsic crystal defects, which is directly observed experimentally by HRTEM. This is the first time that we have found the tunable optical and ferromagnetic behavior of Ba doped nanocrystalline LaB₆. Thus, nanocrystalline La_1−xBa_xB₆, as multi-functional materials, should open up a new route to extend the optical and magnetic applications of LaB₆ nanopowder.