Preparation, Structures And Properties Of Co-Doped (La, Sr)TiO_3-δ Diluted Magnetic Semiconductors

Diluted magnetic semiconductors (DMSs) are one of the important supporting materials for the new-generation of spintronics. Preparing DMSs with room temperature ferromagnetism (RTFM), exploring the origin of RTFM, and applying DMSs to spintronics are becoming the hot-spot topic in the field of spintronics. We prepared (La,Sr)TiO_3-δ (LSTO) and Co-doped LSTO nanocrystals through solvothemal technique combined with post-annealing process. After that, the concentration of Co dopant, the annealing atmosphere, temperture, time and other conditions were investigated. It was found that all these preparation parameters had effect on the local structure and magnetic properties. We focused our research on the correlations between the local structure of Co/C and magnetic properties. Thus, the origin of RTFM is disclosed.It is shown that well crystallized Co-doped LSTO nanocrystals can be obtained successfully through solvothemal technique combined with annealing process. The concentrations of dopant and annealing atmosphere, time and temperature were found intimately correlated to the magnetic properties. When the doping concentration is low than 5 at.%, the ferromagnetism of our samples is of intrinsic property. At the same time, we found that the ferromagnetism has relationship with the concentration of Co dopant and the amorphous C which is remained after annealing. Through controlling the annealing atmosphere and time, we can synthesize single-phase Co-doped LSTO nanocrystals. Based on the RTFM of Co-doped LSTO, We analyzed the effects of structural defects and amorphous C on ferromagnetism, and demonstrated that the RTFM is profoundly correlated with structural defects which are induced in the process of high-purity Ar annealing. The involved coupling-mediated interactions between C and Co may be just the by-products of structural defects. Through the bound magnetic polarons (BMP) model, the origin of RTFM of our samples is then clarified.The research results also show that Co-doped LSTO nanocrystals will have CoO second phase when the Co doping concentration is not lower than 5 at.%. According to the interesting phenomenon of exchange bias, we speculate that the RTFM of our samples is probably due to the collection of the nano-CoO nanocrystals or few amorphous Co metallic impurities.