Omelyanchik Alexander, Salvador María, D'Orazio Franco, Mameli Valentina, Cannas Carla, Fiorani Dino, Musinu Anna, Rivas Montserrat, Rodionova Valeria, Varvaro Gaspare, Peddis Davide
Institute of Structure of Matter-CNR, Monterotondo Stazione, 00016, Rome, Italy.
Immanuel Kant Baltic Federal University, 236041 Kaliningrad, Russia.
Nanomaterials (Basel). 2020 Jun 30;10(7):1288. doi: 10.3390/nano10071288.
The effect of the annealing temperature on the magnetic properties of cobalt ferrite nanoparticles embedded in an amorphous silica matrix (CoFeO/SiO), synthesized by a sol-gel auto-combustion method, was investigated by magnetization and AC susceptibility measurements. For samples with 15% w/w nanoparticle concentration, the particle size increases from ~2.5 to ~7 nm, increasing from 700 to 900 °C. The effective magnetic anisotropy constant () increases with decreasing , due to the increase in the surface contribution. For a 5% w/w sample annealed at 900 °C, is much larger (1.7 × 10 J/m) than that of the 15% w/w sample (7.5 ×10 J/m) annealed at 700 °C and showing comparable particle size. This indicates that the effect of the annealing temperature on the anisotropy is not only the control of the particle size but also on the core structure (i.e., cation distribution between the two spinel sublattices and degree of spin canting), strongly affecting the magnetocrystalline anisotropy. The results provide evidence that the magnetic anisotropy comes from a complex balance between core and surface contributions that can be controlled by thermal treatments.
通过磁化和交流磁化率测量，研究了采用溶胶-凝胶自燃法合成的嵌入非晶二氧化硅基质（CoFeO/SiO）中的钴铁氧体纳米颗粒的退火温度对其磁性能的影响。对于纳米颗粒浓度为15%w/w的样品，随着退火温度从700℃升高到900℃，粒径从约2.5nm增加到约7nm。由于表面贡献的增加，有效磁各向异性常数（）随粒径减小而增大。对于在900℃退火的5%w/w样品，其（1.7×10 J/m）远大于在700℃退火且粒径相当的15%w/w样品（7.5×10 J/m）。这表明退火温度对各向异性的影响不仅在于控制粒径，还在于核心结构（即两个尖晶石亚晶格之间的阳离子分布和自旋倾斜程度），这强烈影响磁晶各向异性。结果表明，磁各向异性来自于核心和表面贡献之间的复杂平衡，这种平衡可通过热处理来控制。
