Manh D H, Thanh T D, Phan T L, Yang D S
Institute of Materials Science, Vietnam Academy of Science and Technology 18 Hoang Quoc Viet Hanoi Viet Nam
Department of Physics, Hankuk University of Foreign Studies Yongin 449-791 South Korea.
RSC Adv. 2023 Mar 13;13(12):8163-8172. doi: 10.1039/d3ra00525a. eCollection 2023 Mar 8.
We have used the coprecipitation and mechanical-milling methods to fabricate CoFeO nanoparticles with an average crystallite size () varying from 81 to ∼12 nm when changing the milling time ( ) up to 180 min. X-ray diffraction and Raman-scattering studies have proved the samples crystalizing in the spinel structure. Both the lattice constant and residual strain tend to increase when () increases (decreases). The analysis of magnetization data has revealed a change in the coercivity ( ) towards the hard-magnetic properties. Specifically, the maximum is about 2.2 kOe when = 10 min corresponding to ≈ 29 nm; beyond this () value, gradually decreases. Meanwhile, the increase of always reduces the saturation magnetization ( ) from ∼69 emu g for = 0 to 35 emu g for = 180 min. The results collected as analyzing X-ray absorption data have indicated a mixed valence state of Fe and Co ions. We think that the migration and redistribution of these cations between the tetrahedral and octahedral sites together with lattice distortions and defects induced by the milling process have impacted the magnetic properties of the CoFeO nanoparticles.
我们采用共沉淀法和机械研磨法制备了CoFeO纳米颗粒，当研磨时间（）延长至180分钟时，其平均晶粒尺寸（）从81纳米变化至约12纳米。X射线衍射和拉曼散射研究证明样品结晶为尖晶石结构。当（）增加（减小）时，晶格常数和残余应变均趋于增大。对磁化数据的分析揭示了矫顽力（）向硬磁特性的转变。具体而言，当 = 10分钟（对应 ≈ 29纳米）时，最大 约为2.2 kOe；超过此（）值后， 逐渐减小。同时， 的增加总是会使饱和磁化强度（）从 = 0时的约69 emu g降低至 = 180分钟时的35 emu g。分析X射线吸收数据所收集的结果表明Fe和Co离子处于混合价态。我们认为，这些阳离子在四面体和八面体位点之间的迁移和重新分布，以及研磨过程引起的晶格畸变和缺陷，共同影响了CoFeO纳米颗粒的磁性能。
