New Progress in Preparing Ferromagnetic and Electrical Materials Containing Cobalt Iron Oxide

Nano-cobalt iron oxide is also called nano-CoFe₂0₄, a nanoparticle material composed of iron and cobalt elements. It has a high specific surface area and good magnetic properties, and is often used in catalysis, batteries, storage media and other fields.

With the increasing requirements for next-generation data storage, there is an urgent need for materials with stronger reliability and faster data transmission speeds. Magnetic materials have been used in magnetic random access memories (MRAM) for data writing by adjusting the magnetization state.

However, due to the problems of high energy consumption and slow writing speed of this technology, in order to increase the writing speed, it is a feasible strategy to use ferroelectric random access memory (FeRAM) devices to replace traditional MRAM. In the process, despite improving write speeds, FeRAM devices also suffer from slow read speeds. Therefore, multiferroic materials with coupled ferroelectric and ferromagnetic sequences achieve fast mixed read and write operations and become an ideal material choice for high-performance data storage devices. However, single-phase multiferroic materials are extremely rare in nature and their magnetoelectric (ME) coupling effects are also limited.

Some researchers used supercritical carbon dioxide (SC CO₂) to help realize the alternate assembly and growth of BaTiO₃ (BTO) and CoFe₂0₄ (CFO) two-dimensional nanostructures, and successfully obtained a two-dimensional nanocomposite material with BTO and CFO lattice coupling. Under the action of SC CO₂, the matching between the BTO and CFO lattices will cause corresponding axial strains in the respective lattice, further inducing enhanced BTO ferroelectricity and CFO ferromagnetism through spin polarization. The coupling exhibits an unprecedentedly high coupling coefficient (325.8 mV cm^-1 Oe^-1).

High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) was used to study the morphology of the nanostructure, and a clear lattice structure and obvious two-phase interface could be seen. Analytical data revealed that structural distortions were found in the lattice structure of the BTO (110) facet. The atomic spacing of Ba atoms along the c-axis direction on the (110) plane is 4.18 Å, which is 3.64% larger than the c-lattice constant (4.033 Å), indicating that BTO is stretched along the octahedral axis. The effective coupling between BTO and CFO is also confirmed by the organic distribution of various elements in the EDS plot.

Further research showed that with the help of SC CO₂, both the thickness and lateral dimensions of the BTO-CFO nanocomposite will decrease with the increase of CFO content, which is beneficial to achieve the interaction between the components. The effective interaction will help the lattice generate specific biaxial strains, thereby effectively enhancing the ferroelectricity of BTO and the ferromagnetism of CFO, ultimately enhancing the magnetoelectric coupling of the nanocomposite through spin-lattice interaction.

This work demonstrates a new idea for preparing multiferroic nanocomposites, opens up the boundaries of using CO₂ to prepare multifunctional materials, and realizes the lattice structure of CO₂-controlled materials.

Reference

1. CO₂-Induced Spin-Lattice Coupling for Strong Magnetoelectric Materials
   Adv. Sci., 2023