Curie’s Law

Curie’s law was introduced and discovered by a French physicist, Pierre Curie. According to Curie’s law, a paramagnetic material’s magnetisation is directly proportional to the applied magnetic field. However, if the material is heated, then the magnetisation is inversely proportional to the temperature. Almost all the elements and some compounds are paramagnetic. Paramagnetism is shown in compounds containing palladium, iron, platinum, and some other rare earth elements. Read on to know more about Curie’s law statement and formula in detail.

Classification of Magnets 

Magnets can be classified in two ways: 

1. According to their occurrence 

Magnets occur in two ways which are natural and artificial. 

• Natural magnets are present naturally on earth. Examples of naturally occurring magnets are Lodestone, Pyrrhotite, Columbite. Lodestones are the strongest natural magnet and are also called magnetite.

• Artificial magnets are man-made magnets, and they are available in various shapes such as horseshoe, bar, disc, etc. 

2. According to their use 

There are three types of magnets based on their usage. They are:

• Permanent magnets

• Electromagnets 

• Temporary magnets

Permanent magnets- They emit magnetic fields without the requirement of an external source of magnetism. All naturally occurring magnets are permanent magnets. They do not lose their magnetic power once magnetised. For example, ceramic, Alnico, Neodymium Iron Boron. 

Temporary magnets-These are magnetised for a short period when they are present near magnetic fields. They lose their magnetism once the magnetic field is removed–for instance, nails and paper clips. 

Electromagnets- These are tenacious magnets consisting of wire coils wrapped around iron metalcore. These magnets are dependent on the strength of the electric current and the number of wire coils. These electromagnets are used in electric motors, televisions, telephones, and many other devices. 

Curie’s Law Formula 

Curie’s law can be represented in the following equation:

M= C x (B / T )

Where, 

• M stands for magnetism 

• C stands for curie constant 

• B stands for magnetic field 

• And T stands for temperature.

What is Diamagnetism, Ferromagnetism and Paramagnetism? 

Diamagnetism, ferromagnetism, and paramagnetism refer to how different materials respond to the same magnetic field. The main difference is that diamagnetism forms an opposite magnetism to the magnetic field and disappears once the external magnetic field is removed. 

Paramagnetism is when magnetism is formed in the same direction as the external magnetic field, and this also disappears once the magnetic field is removed. Whereas ferromagnetism is a type of magnetism where the material forms magnetism in the same direction as the external magnetic field, the magnetism retains when the magnetic field is removed. 

• Diamagnetism

It is the weakest of the three. It is magnetised weakly when placed in the external magnetic field. This happens when the electrons in the orbit spin and produce a spin magnetic moment. In this, the magnetic moments of the atom and the orbital magnetic moments become zero—for example, copper, silver, and silicon.

• Ferromagnetism 

This happens when the unpaired electrons in the atoms have a net magnetic moment. These materials retain their magnetic properties even after the magnetic field is removed. Ferromagnetic items move from the weaker to the stronger parts of external fields. For example, iron, cobalt, and nickel. 

• Paramagnetism 

It is a kind of magnetism where materials are weakly attracted to the magnetic field and form either an internal or an induced magnet. Paramagnetic materials include almost all chemical elements and some compounds. They have higher magnetic permeability, which is higher than 1, and are attracted to the magnetic field. Examples of paramagnetic materials are aluminium, gold, oxygen, etc. 

Other Terms related to Curie’s Law 

• Magnetic susceptibility – It is used to measure how much material will be magnetised in the external magnetic field. 

• Permeability- It is the measure of the ability of the material to support the formation of the magnetic field 

• Curie point- It is the temperature where some materials lose their magnetic properties. 

• Curie constant- This is a property that depends on the material related to their magnetic susceptibility to their temperature. 

Relationship between Curie’s law and Curie-Weiss law 

According to Curie’s law, the magnetisation of any paramagnetic substance is directly proportional to the applied magnetic field. It can be represented as M= C x (B/T). Curie constant is represented as,

 C = (μ0μ2B/3kB)*ng²J(J + 1) 

where, 

• kB represents Boltzmann’s constant

• n represents magnetic atoms per volume 

• g represents lande factor, μB is Bohr magneton 

• j represents the angular moment

Now the fluctuations that occur in the curie temperature are because of the changes in magnetic moments of the element. Therefore the more accurate method to represent Curie law is through Curie Weiss law. 

The equation for Curie-Weiss law is,

χ =M/H=Mμ0/B = C/T

Where,

μ0 is the permeability of free space. 

Conclusion 

Curie’s law and Curie’s temperature are important topics in magnetism. Some properties of magnetic fields are that they originate from the magnetic north pole and end at the south pole. They are denser near the poles but rarer at other places and do not intersect one another. The magnetic behaviour of a particular magnet is identified by the alignment of atoms in a particular substance. In this article, we learned that magnetic susceptibility is inversely proportional to temperature. The magnetisation of a substance is directly proportional to the Curie’s constant.