What is diamagnetism and diamagnetic materials
Diamagnetic materials are repelled by a magnetic field, the applied magnetic field creates an induced magnetic field in them in the opposite direction, causing a repulsive force. Conversely, paramagnetic and ferromagnetic materials are attracted by a magnetic field. For diamagnetic materials, the magnetic flux decreases, and for paramagnetic materials, the magnetic flux increases.
The phenomenon of diamagnetism was discovered by Sebald Justinus Brugmans, who in 1778 noticed that bismuth and antimony were repelled by magnetic fields. The term diamagnetism was coined by Michael Faraday in September 1845. He realized that all materials actually have some sort of diamagnetic effect on external magnetic fields.
Diamagnetism is probably the least known form of magnetism, despite the fact that diamagnetism occurs in almost all substances.
We are all used to magnetic attraction because of how often ferromagnetic materials and since they have enormous magnetic susceptibility.On the other hand, diamagnetism is almost unknown in everyday life because diamagnetic materials in general have very little susceptibility and therefore repulsive forces are almost negligible.
The phenomenon of diamagnetism is a direct consequence of the actions of the Lenz forcesoccurs when a substance is placed in a space where there are magnetic fields. Diamagnetic substances cause the weakening of any external magnetic field in which they are located. The Lenz field vector is always directed against the externally applied field vector. This is true in any direction, regardless of the orientation of the diamagnetic body with respect to the applied field.
Any body made of diamagnetic material not only weakens the external field due to the influence of the Lenz reaction, but also experiences the action of a certain force if the external field is non-uniform in space.
This force, which depends on the direction of the field gradient and is independent of the direction of the field itself, tends to move the body from the region of relatively strong magnetic field to the region of weaker field—where changes in electron orbits will be minimal.
The mechanical force acting on a diamagnetic body in a magnetic field is a measure of the atomic forces that tend to keep the orbital electrons in spherical orbits.
All substances are diamagnetic because their basic constituents are atoms with orbital electrons… Some substances create both Lenz fields and spin fields. Due to the fact that spin fields are usually much stronger than Lenz fields, when fields of both types occur, the effects due to spin fields usually predominate.
Diamagnetism resulting from changes in electron orbits is usually weak because the local fields acting on individual electrons are much stronger than the applied external fields, which tend to change the orbits of all the electrons. Since the orbital changes are small, the Lenz reaction associated with these changes is also small.
At the same time, diamagnetism is due to random motion plasma elements, manifests itself much more strongly than diamagnetism associated with a change in electron orbits, since plasma ions and electrons do not experience the action of large binding forces. In this case, relatively weak magnetic fields significantly change the particle trajectories.
The diamagnetism of many individual microscopic particles moving along trajectories of different types can be considered as the result of the influence of the equivalent current circuit surrounding the body whose substance contains these particles. Measuring this current allows the diamagnetism to be quantified.
Diamagnetic levitation:
Some examples of diamagnetic materials are water, the metal bismuth, hydrogen, helium and other noble gases, sodium chloride, copper, gold, silicon, germanium, graphite, bronze, and sulfur.
In general, diamagnetism is practically invisible, except for the so-called superconductors… Here the diamagnetic effect is so strong that superconductors even move over a magnet.
The demonstration of diamagnetic levitation used a plate of pyrolytic graphite—it is a highly diamagnetic material, that is, a material with a very negative magnetic susceptibility.
This means that in the presence of a magnetic field, the material becomes magnetized, creating an opposing magnetic field that causes the material to be repelled by the source of the magnetic field. This is the opposite of what happens with paramagnetic or ferromagnetic materials that are attracted to magnetic field sources (eg iron).
Pyrolytic graphite, a material with a special structure that gives it great diamagnetism. This, combined with its low density and the strong magnetic fields that are achieved with neodymium magnets, makes the phenomenon visible as it is in these pictures.
It has been experimentally confirmed that diamagnetic materials have:
- The relative magnetic permeability is less than one;
- Negative magnetic induction;
- Negative magnetic susceptibility, practically independent of temperature.
At temperatures below critical temperatures, during the transition of a substance into a superconducting state, it becomes an ideal diamagnet:Meissner effect and its use