The ‘Barnett effect’ is the magnetization of any uncharged body as it spins on its long axis. This is caused by the coupling between the angular momentum of the electronic spins and also by the rotation of the rod. The Barnett effect was first said to come into observation by Sir Samuel Barnett in the year 1915.
In short, we can say that the Barnett effect is the magnetization of an uncharged body when it is spun on its own axis. Samuel Barnett was an American physicist whose work had been prominent in other fields of physics as well. The magnetization of an uncharged body generally occurs parallel to the axis of its spin.
Barnett, who discovered this effect was motivated by a prediction by Owen Richardson in the year around 1908. Later it was named as the Einstein de Haas effect, which means if we magnetize a ferromagnetic substance, then it can induce a mechanical rotation in that substance. He instead started to look for the opposite effect. He then found that spinning a ferromagnet could tend to change its magnetization. He established the effect with a long series of experiments between the years of 1908 and 1915.
At the very start, Arabgol and his supervisor Mr. Tycho Sleator wanted to take out the rotation of the body when used in their experiments by transfer of the orbital angular momentum of the light into the sample. With the proceedings of the experiment they soon realized that this technique didn’t really work out and thus they decided to employ an exact and functional method that used a material that is a mechanical spinner to drive the rotation.
Arabgol stated that if they allow the mechanical spinner to spin a large sample of water to the speed somewhat close to 15,000 revolutions per second, and then they could finally demonstrate the nuclear Barnett effect. In their experiments, Arabgol and Sleator used a good spinner turbine to rotate the sample of water taken by them, up to very high speeds. They also used a nuclear magnetic resonance (NMR) machine that is specially designed to operate easily at low and even at very low frequencies. This is in contrast with the commercial NMR systems, which operate at high frequencies.
Arabgol and Sleator were the first two-person to magnetize protons which helped in attaining a reliable observation of the nuclear Barnett effect. Another interesting point of their study was that the magnetization which they observed had nothing to do with magnetic fields. This point is of great importance particularly since the researchers have so far magnetized objects by applying a known magnetic field to them. The study carried out by Arabgol and Sleator somewhere proves that there are some other mechanisms that can induce magnetization without necessarily creating and applying a magnetic field.
If we look at the theoretical standpoint, then these previous observations somewhere enhance the current understanding of our knowledge of the relationship between magnetization and the rotation. On the other hand, if we look at the practical standpoint, they could help in the development of ultra-low frequency NMR systems by introducing some new techniques for inducing magnetization without the use of any kind of magnets.
The reversibility of the production of these kinds of fields was investigated for both hollow as well as for solid cylinders. In the first case of the hollow cylinder, the effects analogous to the flux trapping were observed. In case if the sample is cooled below a specific point while it is in rotation, then the London field will appear only when the rotation speed has been changed. While if we look at the case of the solid cylinder, then the effects analogous to those effects that are associated with frozen flux were observed.
The magnetization and Gravito-magnetization that we obtain through the rotation of a body by aligning the angular momentum of the substance mechanical is just similar to the magnetization and the Gravito-magnetization that we obtain by applying an external magnetic field on the body or by applying an external gravitomagnetic field on that same body when it is at rest.
Thus, with our understanding, we can say that the Barnett effect should also exist for protons that are located in a bulk sample. But we know that the magnetic moment of a proton is nearly three orders of magnitude as compared to that of the electrons. This renders its magnetization due to the fact that its rotation is too small and also easily masked by other experimental noise.
One reason that the search for the nuclear Barnett effect took too long was that this effect lacks genuine practical applications. In fact, it was an application that has made Sleator on the trail. He, along with some other people and some graduate students of that time, wanted to develop an MRI technique that did not use a large external magnetic field to polarize the protons. Then, making the use of the nuclear Barnett effect seemed like a possible strategy that can be performed. After working on the project, it was finally concluded that even measuring the effect was a really big challenge.
Around 2006, a paper came up that reported the detection of proton polarized with the help of a superconducting quantum interference device (called SQUID), which was a magnetometer that can measure extremely small magnetic fields also. Hahn realized that this same technique might also be used to detect the nuclear Barnett effect. Hahn and other scientists and students spent many numbers of hours in designing SQUID experiments and performing computer calculations to observe the expected effect.
Through all the above depictions, we can certainly say that the Barnett Effect would be the only physical effect that would allow the production of some important magnetic field despite the fact that they are associated with those bodies that have an extremely small magnetization.