Hossain M D, Mayanovic R A, Dey S, Sakidja R, Benamara M
Department of Physics, Astronomy & Materials Science, Missouri State University, Springfield, MO 65897, USA.
Phys Chem Chem Phys. 2018 Apr 18;20(15):10396-10406. doi: 10.1039/c7cp08597d.
We have synthesized bimagnetic core-shell nanoparticles containing a first-of-its-kind Ni(ii)-chromia nanophase shell and a well-defined, epitaxial core-shell interface. Magnetic measurements reveal a substantial coercivity of the nanoparticles and a significant exchange bias effect between the antiferromagnetic chromia core and the ferromagnetic Ni(ii)-chromia shell at low temperatures. The ferromagnetism and a weak exchange bias effect are found to persist to room temperature in the core-shell nanoparticles of ∼57 nm average size. Our first principles Density Functional Theory (DFT) calculations confirm that the novel corundum-structured Ni(ii)-chromia phase has an equilibrium cluster-localized ferromagnetic spin configuration. In addition, the DFT-based calculations show that the Ni(ii)-chromia phase is a Mott-Hubbard insulator, with a narrowed energy band gap and increased covalent bonding due to strong hybridization between Ni 3d and O 2p levels in the upper portion of the valence band and within the band gap region. The antiferromagnetic, ferromagnetic and magnetoelectric properties of our core-shell nanoparticles make these well suited for patterned recording media and biomedical applications.
我们合成了一种双磁核壳纳米颗粒，其包含首创的Ni(ii)-氧化铬纳米相壳层以及明确的外延核壳界面。磁性测量结果显示，这些纳米颗粒具有显著的矫顽力，并且在低温下反铁磁氧化铬核与铁磁Ni(ii)-氧化铬壳层之间存在明显的交换偏置效应。在平均尺寸约为57 nm的核壳纳米颗粒中，铁磁性和微弱的交换偏置效应在室温下依然存在。我们的第一性原理密度泛函理论（DFT）计算证实，新型刚玉结构的Ni(ii)-氧化铬相具有平衡的团簇局域铁磁自旋构型。此外，基于DFT的计算表明，Ni(ii)-氧化铬相是一种莫特-哈伯德绝缘体，由于价带上部和带隙区域内Ni 3d和O 2p能级之间的强杂化作用，其能带隙变窄且共价键增强。我们核壳纳米颗粒的反铁磁、铁磁和磁电特性使其非常适合用于图案化记录介质和生物医学应用。
