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Dependence of the Ferromagnetism on Vacancy Defect in Annealed In 2 O 3 Nanocrystals: A Positron Annihilation Study
Author(s) -
Wang Zihao,
Dong Xiumei,
Chen Zhiyuan,
Xiong Houhua,
Gao Jie,
Du Jifu,
Tang Xiuqin,
Zhang Quankun,
Qian Libing,
Chen Zhiquan
Publication year - 2021
Publication title -
physica status solidi (a)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.532
H-Index - 104
eISSN - 1862-6319
pISSN - 1862-6300
DOI - 10.1002/pssa.202000631
Subject(s) - annealing (glass) , vacancy defect , materials science , ferromagnetism , crystallinity , condensed matter physics , transmission electron microscopy , nanocrystal , magnetization , grain size , raman spectroscopy , analytical chemistry (journal) , crystallography , nanotechnology , metallurgy , chemistry , magnetic field , physics , chromatography , quantum mechanics , optics , composite material
In 2 O 3 nanoparticles are fabricated by a sol–gel method, and annealed under air atmosphere from 400 to 1200 °C. X‐ray diffraction patterns display that all samples are the cubic bixbyite structure, grain size remains nearly unchanged below 700 °C, but remarkable increases from 35 to 72 nm after annealing up to 1200 °C. Electron microscopy also confirms the grain growth during high‐temperature annealing, and the transmission electron microscopy characterizes good crystallinity inside the grains. Raman spectroscopy indicates that the crystallinity of annealed samples is improving and the concentration of oxygen vacancies is decreasing with the increase in annealing temperature. Positron annihilation lifetime measurements identify that there are a large number of monovacancies and vacancy clusters on the surface of nanoparticles. With the increase in annealing temperature, the monovacancies keep a slight recovery and their concentration increases, but the vacancy clusters become smaller vacancies and their concentration decreases. Room‐temperature ferromagnetism exists in the samples after annealing at 400–1000 °C, and the magnetization decreases gradually with the increase in annealing temperature, which is in coincidence with the recovery of vacancy clusters after annealing. These findings suggest that ferromagnetism in annealed In 2 O 3 nanocrystals might be due to the indium–oxygen vacancy clusters rather than grain size effects.