Is Graphite Magnetic ?

In materials science, graphite is a unique material de carbono, because of its special structure and properties. It plays a key role in many fields such as writing and industry. However, its magnetism is often ignored and the public’s cognition is vague. The research on the magnetism and nature of graphite is not only related to the improvement of basic theory. But also has great potential in emerging fields such as quantum computing.

Is graphite magnetic?

Basic properties of graphite

The graphite crystal has a typical layered structure. And the carbon atoms in each layer are connected to each other by covalent bonds, forming a hexagonal honeycomb plane grid. And the electrons can move freely in the layer, giving the graphite good electrical conductivity, similar to the characteristics of metal bonds. The layer and layer are maintained by weak van der Waals force, and the distance is large. Macroscopically, graphite has soft texture, metallic luster, relatively stable chemical properties, high temperature resistance. Resistance to a variety of acid and alkali erosion, unique structure and properties are the basis for exploring its magnetism.

The nature of magnetism

Magnetism comes from the motion and spin of electrons inside atoms. The orbital magnetic moment of the electrons orbiting the nucleus is like a miniature ring current. The electron itself also has a spin magnetic moment, similar to the spin of a tiny top. In most materials, the interaction of atomic magnetic moments is complex. If the atomic magnetic moments spontaneously align in the same direction within a certain range, the material exhibits ferromagnetism, such as iron, cobalt, nickel. The magnetic moments of some materials are opposite and parallel to each other, but the size is different. And there are net magnetic moments, showing ferromagnetism. There are also some materials atomic magnetic moment reverse parallel and completely offset, macro non-magnetic, said diamagnetism. When the external magnetic field, the electron orbit will produce a weak additional magnetic moment against the external field. This is the diamagnetic source.

The diamagnetic properties of graphite

Grafite are essentially diamagnetic substances. In the absence of external magnetic field, the sum of magnetic moments of each atom inside graphite is almost zero. So it does not show magnetism at large. But when a magnetic field is applied to the outside world, according to the principle of electromagnetic induction, the electron motion state inside graphite changes. In order to prevent the change of magnetic flux of the external magnetic field, electrons will generate an additional motion. This in turn forms an induction magnetic moment opposite the direction of the external magnetic field. This induction magnetic moment is very weak, so that the anti-magnetic performance of graphite is not obvious. Its magnetic susceptibility is usually negative and the value is very small, about the order of magnitude of -10^-5.

External factors affecting the graphite magnetic properties

Temperature has a significant effect on the magnetic properties of graphite. As the temperature increases, the thermal motion of the atoms inside the graphite intensifies. And this increase in thermal motion interferes with the orbital motion of the electrons. It in turn affects the response of the electrons to the applied magnetic field. Specifically, as the temperature increases, the absolute value of the diamagnetic susceptibility of graphite will decrease slightly. But this change is relatively slow. And the diamagnetism of graphite can be approximately considered to remain relatively stable within a certain temperature range.

In addition to temperature, the strength and frequency of the external magnetic field will also affect the magnetic properties of graphite. When the strength of the external magnetic field is weak, the diamagnetic response of graphite basically conforms to the linear law. That is, the magnetization is proportional to the strength of the external magnetic field. However, when the strength of the external magnetic field increases to a certain extent, the quantum mechanical effect begins to appear. And the diamagnetic properties of graphite will gradually deviate from the linear relationship, showing more complex magnetic behavior. In addition, for alternating magnetic fields, if the frequency is high, the response speed of the electrons inside the graphite may not be able to keep up with the change in the magnetic field. This results in a change in its diamagnetism.

Is graphite oxide magnetic?

Graphite oxide is a graphite derivative obtained by oxidizing graphite. During the oxidation process, a large number of oxygen-containing functional groups such as hydroxyl, carboxyl, and epoxy groups are introduced into the structure of graphite. The existence of these oxygen-containing functional groups greatly changes the original layer structure of graphite. This increases the layer spacing, and destroys the original electron conjugation system of graphite. Resulting in a significant decrease in its electrical conductivity.

In terms of magnetism, due to the existence of unpaired electrons in the oxygen-containing functional groups introduced in the oxidation process. These unpaired electrons have a spin magnetic moment, making graphite oxide have a certain paramagnetism. When the degree of oxidation is low, the graphite oxide still retains some of the original diamagnetic properties of graphite. At this time paramagnetism and diamagnetism compete with each other, and the macroscopic magnetic performance is not obvious. However, with the deepening of the degree of oxidation, the paramagnetic signal is gradually enhanced. And when it exceeds a certain threshold, paramagnetism will dominate, making the graphite oxide as a whole show paramagnetism. And its magnetic susceptibility becomes positive.

Conclusão

Graphite is a diamagnetic substance, and its diamagnetism is generated by the electron induced magnetic moment under the external magnetic field. It is of great significance in a specific scene. Graphite oxide is paramagnetic because it contains unpaired electrons, and the magnetism varies with the degree of oxidation. In-depth research on the magnetism of the two is conducive to improving the theory, promoting innovative applications. And helping the development of new materials and technologies.