The La-Co co-substituted magnetoplumbite-type (M-type) ferrites $A$Fe$_{12}$O$_{19}$ ($A$ = Ca, Sr and Ba, ion sizes Ca$^{2+}$ $<$ Sr$^{2+}$ $<$ Ba$^{2+}$) with Co compositions around 0.2 have been subjected to $^{59}$Co-NMR. The results show that Co occupies the 4f$_1$, 2a and 12k sites, and that the smaller the $A$ ion, the more Co tends to occupy the 4f$_1$ minority spin site, which is effective in enhancing both uniaxial anisotropy and magnetisation. First-principles total energy calculations based on density functional theory (DFT) of undoped $A$Fe$_{12}$O$_{19}$ and a supercell ($2 \times 2 \times 1$ of the unit cell) in which 1/96 of Fe$^{3+}$ is replaced by Co$^{2+}$ were performed to predict the stable structure and Co occupancy sites. The results show that regardless of $A$, Co is most stable when it occupies the 4f$_1$ site, followed by the 2a and 12k sites with energy differences on the order of 100 meV, and Co practically does not occupy the 2b and 4f$_2$ sites. As the $A$ ion becomes smaller, the energy difference when Co occupies each Fe site tends to increase, and the Co occupancy of the 4f$_1$ site also increases. The site selectivity of Co can be roughly explained as a result of the difference in uniaxial strain along the $c$-axis associated with the difference in $A$. However, the influence of the $A$ ion differs between the R and S blocks and the local strain also has a secondary effect on the Co distribution. Based on these results, the guidelines for improving the performance (anisotropy and magnetisation) of La-Co co-substituted M-type ferrite magnets with a limited amount of Co can be summarised as follows: It is effective to select as small $A$ ions as possible and to post-anneal at low temperature or cool slowly to concentrate Co at the 4f$_1$ site in tetrahedral coordination.
Chemical synthesis and magnetic properties of monodisperse cobalt ferrite nanoparticles
在这项工作中，一个成功的合成磁性钴铁氧体（CoFe 2 O 4）纳米粒子。合成的CoFe 2 O 4纳米粒子具有球形形状，在所选择的溶剂中高度单分散。研究了不同反应条件如温度、反应时间和不同封端剂对产物物相和形貌的影响。扫描透射电子显微镜显示，这些纳米粒子的大小可以通过改变反应条件来控制。X射线衍射和能量色散X射线光谱证实了立方对称的CoFe 2 O 4尖晶石结构的形成。由于优化的反应参数，每个纳米颗粒被证明是一个单一的磁畴的直径范围从6到16 nm。最后，磁性研究表明，所获得的纳米粒子是超顺磁性的小矫顽力值约315 Oe和饱和磁化强度为58 emu/g在室温下。这些结果使得钴铁氧体纳米颗粒有望用于先进的磁性纳米器件和生物磁性应用。
High coercivity induced by mechanical milling in cobalt ferrite powders
在这项工作中，我们报告的研究亚铁磁性氧化物CoFe 2 O 4的磁行为处理的机械研磨与不同的磨球。采用简单的水热法制备了钴铁氧体纳米粒子，并在500 ℃下进行了退火处理。未研磨的样品呈现约1.9kOe的磁化率、69.5emu/g的饱和磁化强度和0.42的剩磁比。球磨后，两种样品的磁化强度分别为4.2和4.1kOe，饱和磁化强度分别为67.0和71.4emu/g。这些样品的剩磁比MR/MS分别增加到0.49和0.51。为了研究这些样品的磁行为的微观结构的影响，我们使用X射线粉末衍射（XPD），透射电子显微镜（TEM），和振动样品磁强计（VSM）。通过Williamson-Hall图的XPD分析用于估计样品中由机械研磨引起的平均微晶尺寸和应变。
Room temperature spin filtering in epitaxial cobalt-ferrite tunnel barriers
我们报告的直接实验证据，室温自旋过滤的磁性隧道结（MTJ）含有CoFe 2 O 4隧道势垒通过隧道磁阻（TMR）测量。Pt（111）/CoFe_2 O_4（111）/γ-Al_2 O_3（111）/Co（0001）全外延MTJ的生长是为了获得能够在室温下工作的高质量系统。自旋极化输运测量显示，在2K和290 K下，TMR值分别为-18%和-3%。此外，TMR比遵循一个独特的偏置电压依赖性，这在理论上已经被预测为在MTJ中包含磁势垒的自旋过滤的签名。因此，CoFe 2 O 4隧道势垒提供了一个模型系统，以调查在很宽的温度范围内的自旋过滤。
Magnetoelectric Coupling in Nickel-Cobalt Ferrite and Lanthanum Ferrite Heterostructure Composites: Experimental Evidence and Simulation-Driven Insights
In-depth investigations of size and occupancies in cobalt ferrite nanoparticles by joint Rietveld refinements of X-ray and neutron powder diffraction data
Catalytic effect of the spinel ferrite nanocrystals on the growth of carbon nanotubes
通过溶胶-凝胶法制备了三种铁氧体纳米催化剂：（i）铜铁氧体（CuFe 2 O 4），（ii）其中钴被镍取代的铁氧体（NixCo 1-xFe 2 O 4，其中x= 0，0.2，0.4，0.6），和（iii）其中镍被锌取代的铁氧体（ZnyNi 1-yFe 2 O 4，其中y= 1，0.7，0.5，0.3）。X射线衍射分析表明，样品为立方尖晶石结构。我们通过FE-SEM图像获得了10-70 nm范围内的晶粒尺寸，并通过VSM获得了它们的磁性。接着，通过CCVD法在这些纳米催化剂上生长碳纳米管。我们发现，这些纳米晶体对碳纳米管生长的催化作用取决于阳离子分布在八面体和四面体网站，结构各向同性和催化能力，由于阳离子。我们的研究可以应用于寻找合适的候选掺杂铁氧体纳米晶体作为碳纳米管生长的催化剂。更有趣的是，碳纳米管的产量可以被认为是研究铁氧体催化活性的间接工具。
