Increased room temperature ferromagnetism in Co-doped tetrahedral perovskite niobates

Abstract

Dilute magnetic semiconductors (DMSs), such as (In, Mn)As and (Ga, Mn)As prototypes, are limited to III–V semiconductors with Curie temperatures ( T c ) far from room temperature, thereby hindering their wide application. Here, one kind of DMS based on perovskite niobates is reported. BaM x Nb (1− x ) O 3− δ ( M = Fe, Co) powders are prepared by the composite-hydroxide-mediated method. The addition of M elements endows BaM x Nb (1− x ) O 3− δ with local ferromagnetism. The tetragonal BaCo x Nb (1− x ) O 3− δ nanocrystals can be obtained by Co doping, which shows strong saturation magnetization ( M sat ) of 2.22 emu g −1 , a remnant magnetization ( M r ) of 0.084 emu g −1 and a small coercive field ( H c ) of 167.02 Oe at room temperature. The ab initio calculations indicate that Co doping could lead to a 64% local spin polarization at the Fermi level ( E F ) with net spin DOS of 0.89 electrons eV −1 , this result shows the possibility of maintaining strong ferromagnetism at room temperature. In addition, the trade-off effect between the defect band absorption and ferromagnetic properties of BaM x Nb (1− x ) O 3− δ is verified experimentally and theoretically.

In Situ Formation of Ba3CoNb2O9/Ba5Nb4O15 Heterostructure in Electrolytes for Enhancing Proton Conductivity and SOFC Performance

“…The diffusion of Co into the electrolyte triggered the crystal structure change of Ba 5 Nb 4 O 15 . From the enlarged image (Figure b) in the range of 27–32°, Co 2+ (the ionic radius of 74.5 pm) replaced Nb 4+ (an ionic radius of 68 pm) in the Ba 5 Nb 4 O 15 crystal structure, leading to the diffraction peaks being shifted to a lower angle, by the temperature changing from 510 to 550 °C, and the shifted degree increased due to more being Co incorporated into the Ba 5 Nb 4 O 15 matrix. The XRD analysis of NCAL anode after H 2 exposure and the Ba 3 CoNb 2 O 9 /Ba 5 Nb 4 O 15 electrolyte after exposing in H 2 /air for 2 h at 510 °C are shown in Figures S4 and S5, respectively.…”