title: Observation of nanotwinning and room temperature ferromagnetism in sub-5 nm BiFeO3nanoparticles: a combined experimental and theoretical study.
abstract: Particle size significantly affects the properties and therefore the potential applications of multiferroics. However, is there special particle size effect in BiFeO3, which has a spiral modulated spin structure? This is still under investigation for sub-5 nm BiFeO3. In this report, the structural, electronic and magnetic properties are investigated for chemically synthesized BiFeO3nanoparticles with an average size of 3 nm. We observed nanotwinning features in the specific size regime of the nanoparticles (2-4 nm). A weak Bi-O-Fe coordination and weak covalent nature has been observed in the nanoparticles through high-resolution electron energy loss spectroscopy and theoretical analysis, confirming that BiFeO3nanoparticles a retain rudimentary R3c phase even at sub-5 nm dimensions. The R3c phase of sub-5 nm BiFeO3nanoparticles has also been confirmed using Raman spectroscopy and Raman mapping of the vibrational modes. The nanoparticles display cluster spin glass, room temperature ferromagnetism, and a metamictization-davidite phase. The observation of weak magnetic entropy features confirmed the presence of a weak correlation between the magnetic and ferroelectric components. To support our experimental observations, we have simulated a sub-5 nm BiFeO3nanocluster. Using density functional theory, the ferromagnetic ground state and the presence of a weak covalent nature in the nanocluster is established considering the first Brillouin zone, thus confirming our experimental results. Finding of new physicochemical features in sub-5 nm BiFeO3would be beneficial for the understanding of the fundamental physical and chemical science as well as potential device development.
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China. hqwang@ustc.edu.cn mandar@ustc.edu.cn mmshirolkar@gmail.com.
authors.forename: Mandar M
authors.initials: MM
authors.lastname: Shirolkar
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China. hqwang@ustc.edu.cn mandar@ustc.edu.cn mmshirolkar@gmail.com.
authors.forename: Xiaolei
authors.initials: X
authors.lastname: Dong
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China. hqwang@ustc.edu.cn mandar@ustc.edu.cn mmshirolkar@gmail.com.
authors.forename: Jieni
authors.initials: J
authors.lastname: Li
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China. hqwang@ustc.edu.cn mandar@ustc.edu.cn mmshirolkar@gmail.com.
authors.forename: Shiliu
authors.initials: S
authors.lastname: Yin
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China. hqwang@ustc.edu.cn mandar@ustc.edu.cn mmshirolkar@gmail.com.
authors.forename: Ming
authors.initials: M
authors.lastname: Li
authors.affiliation: Hefei National Laboratory for Physical Sciences at the Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People's Republic of China. hqwang@ustc.edu.cn mandar@ustc.edu.cn mmshirolkar@gmail.com.
authors.forename: Haiqian
authors.initials: H
authors.lastname: Wang