Concept of Adiabatic Demagnetization

The process of removal of a magnetic field from certain materials that serve to lower their temperature is known as adiabatic demagnetization. This procedure delivers a means for cooling a material that is already cold to a small fraction of 1 K, and this method was proposed by William Francis Giauque and chemist Peter Debye.

What is Adiabatic Demagnetization?

Adiabatic Demagnetization uses the paramagnetic nature in some materials to cool those materials, generally in the form of gaseous, into the colder range or millikelvin. To cool solid objects, this method can also be used, but the most extreme cooling in the fractions of a Kelvin range is normally achieved for gasses that have already been greatly cooled, which means low-density gasses.

To obtain extremely low temperatures, the method of adiabatic Demagnetization is widely used. A sample of a paramagnetic salt is magnetized isothermally, which is already cooled to low temperatures by other means. To conduct away any heat that is produced, the sample is often suspended in an atmosphere of helium, and hence this keeps the process isothermal. It is then adiabatically demagnetized when insulated by pumping out the helium. This process can be repeated consecutively that involves isothermal magnetization followed by adiabatic Demagnetization. In this manner, temperatures close to 0 K can be reached. If this process is repeated an infinite number of times, you could actually reach a temperature of absolute zero but not less than that.

What are Paramagnetic Materials?

Paramagnetic materials are the materials in which a magnetic field that is parallel to the applied field is induced when an outside magnetic field is applied to these materials. The strength of field strength decides the number of particles that align with the applied field, i.e. more particles are aligned with the field if there is a higher field strength.

What is the Process of Adiabatic Demagnetization?

The process of adiabatic Demagnetization includes the following steps:

1. To induce a magnetic field in the region of the sample, first, the sample is cooled and then allowed to touch a cold reservoir, maintaining a constant temperature of around 3-4 K.
2. The magnetic field strength is increased once the sample is in thermal equilibrium with the cold reservoir. Since the particles align with the magnetic field, the system becomes more ordered, and this causes the entropy of the sample to decrease. At this point, the temperature of the sample will be the same as that of the cold reservoir.
3. Then the magnetic field strength is reduced because, from the cold reservoir, the sample is isolated. In reaction to the reduction in the magnetic field strength, the temperature of the sample drops, but its entropy goes on the same. Permitting the sample to be cooled to a very low temperature, this process can be repeated.

Drawbacks of the Adiabatic Demagnetization Process

• The lowest temperatures that can be accomplished using these methods are on the order of 1 millikelvin if the sample material is an electronic paramagnet.
• Because of the weaker interactions between the dipoles, the lowest temperatures that can achieve becomes much lower if the sample is a nuclear paramagnet.

Electronic Paramagnets

The materials with net electromagnetic moments are known as electronic paramagnets. Since the electronic, magnetic moments incline to align themselves with a magnetic field, these materials are paramagnetic in nature.

What is a Magnetic Field? :

What are Nuclear Paramagnets?

The nuclear paramagnets are the materials in which the net magnetic moment is caused by the individual magnetic moments of their nuclei. As compared to the electromagnetic moments, the nuclear magnetic moments are about a thousand times smaller, and hence the dipole interactions are weaker.

Why is It Important to demagnetize a Magnet?

After reading the above information, you must be thinking about why it becomes important to destroy a perfectly good magnet. Well, the answer is simple, a magnet is demagnetized because, in some situations, magnetization is not necessary or desirable.

For instance, Demagnetization is one of the methods to dispose of or remove the data and improve security in data storage devices such as magnetic tape to protect them from easy access.

There are various circumstances in which metallic objects get magnetized and create trouble in their own functioning. In some cases, the problem is that the magnetic field itself presents issues, while in some, the metal will attract other metals.

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