Paramagnetism: Definition, Properties, Curie's Law & Examples

Paramagnetism is a form of magnetism where some materials are weakly attracted by an externally applied magnetic field. They form internal induced magnetic fields in the direction of the applied magnetic field. Paramagnetic materials are attracted towards magnetic fields in which they move from a region of a weaker magnetic field to a stronger magnetic field, this phenomenon is called paramagnetism. These paramagnetic materials consist of most of the elements and some compounds that have unpaired electrons in their valence shells.

Key Terms: Paramagnetic Material, Paramagnetism, Diamagnetic Materials, Curie's Law, Dipole Moment, Ferromagnetic Material, Magnetic Field

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What is Paramagnetism?

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Paramagnetism is a characteristic of materials that are weakly attracted to magnetic fields. When a paramagnetic material is placed in a magnetic field, it moves from weaker to stronger regions in it and produces a magnetic field in the direction of the applied magnetic field. This phenomenon is called paramagnetism.

• In a magnetic field, the individual dipole moments of the atoms in a paramagnetic material get aligned in a single direction (in the direction of the applied magnetic field).
• This produces a magnetic field in the direction of the applied magnetic field.
• In the absence of the applied magnetic field, the magnetic moment of each atom does not interact with each other and results in the termination of the induced magnetic field.
• The magnetic field produced by a paramagnetic material is proportional to the strength of the applied magnetic field.

The video below explains this:

Magnetic Properties of Substances value Detailed Video Explanation:

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Paramagnetic Materials

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Paramagnetic materials are the materials that are attracted in the presence of a strong magnet. The magnetic permeability of the paramagnetic materials or materials showing paramagnetism is greater than or equal to one; magnetic permeability is the ability of a material to form a magnetic field within itself. 

• Paramagnetic materials have an unpaired electron in their valence shell.
• These unpaired electrons are in a constant spinning motion.
• This incessant spin of the electron forms a dipole moment; they act as small magnets themselves.
• However, the dipoles are in random directions and do not interact with one another, so the total magnetic field created by paramagnetic material is zero.

Magnetic field lines through paramagnetic material

Paramagnetic materials are quite different from diamagnetic materials. Diamagnetic materials have paired electrons in the outer valence shell, and they are repelled from the magnetic field, unlike paramagnetic materials.

Read More: Magnetic Poles and its Significance

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Examples of Paramagnetic Materials

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Most of the elements and some compounds are paramagnetic. Some of the examples of materials showing paramagnetism are as follows –

• Sodium
• Calcium
• Aluminium
• Tungsten
• Caesium
• Lithium
• Magnesium

Read More: Bar magnet

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Properties of Paramagnetic Materials

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Paramagnetic materials or the materials showing paramagnetism display the following properties – 

• The unpaired electrons in the atoms of paramagnetic materials are engaged in an incessant dipole moment due to the unpaired electron spin.
• Paramagnetic materials move from a weaker region to a stronger region in a nonuniform electric field.
• The degree of magnetization of paramagnetic materials in an external electric field (i.e. magnetic susceptibility) is positive and small.
• The magnetic permeability of a paramagnetic substance is greater than or equal to one.
• Paramagnetic materials are attracted towards the electric field weakly.
• Temperature is inversely proportional to magnetization in a paramagnetic material.
• When a paramagnetic material is placed in a magnetic field, the dipole moments in it become parallel to the applied magnetic field.

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Curie's law

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According to Curie’s law, paramagnetic materials are magnetically susceptible (can be magnetized), and they show paramagnetism at a wide range of temperatures.

Curie's law states that the magnetic susceptibility of paramagnetic materials is inversely proportional to the temperature.

Where,

• M is the magnetization of the material.
• C is called the material-specific curie's constant.
• T is the temperature in Kelvin.
• B is the applied magnetic field.

From Curie's law, we can infer that when the strength of the applied magnetic field increases or the temperature decreases, the magnetization increases. Magnetization increases until its value reach a specific saturation point. After this value, Curie's law is not valid.

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Curie's Constant

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Curie's constant is a material-specific value that is directly proportional to its magnetization. The Curie constant value for each substance is derived by using the following formula – 

Where,

• μ_B → Bohr magneton
• n → Number of magnetic atoms/molecules per unit volume
• g → Landé g-factor
• J → Angular momentum quantum number
• k_B → Boltzmann constant
• Curie constant unit is given by K.A/T.m

Read More: Difference between Electromagnet and Permanent magnet

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Curie's temperature

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At a certain temperature, the magnetic substances undergo acute changes in their behaviour and properties, this temperature is called Curie's temperature.

• Curie's temperature is also called Curie's point.
• Curie discovered the relationship of temperature with magnetic properties.
• Curie's point is different for different materials.
• A ferromagnetic material becomes paramagnetic above Curie's temperature, but paramagnetic materials suffer no change.

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Previous Year Questions

1. The ferromagnetic substance is converted into paramagnetic substances … [JIPMER 1996]
2. The relative permeability is represented by μ_r … [KCET 2001]
3. A device which converts electrical energy into mechanical energy … [JKCET 1999]
4. A circular loop of radius R, carrying current I, lies in x-y plane … [JEE Advance 1999]
5. When a material is placed in a magnetic field B … [COMEDK UGET]
6. Susceptibility of a magnetic substance is found to depend on temperature … [JEE Advance 1998]
7. The magnetic susceptibility is negative for … [NEET 2016]
8. Which of the following is a paramagnetic group? 
9. Nickel shows ferromagnetic property at room temperature … 
10. Two short bar magnets of length 1cm each have magnetic moments … [JEE Main 2013]
11. According to Curie's law, the magnetic susceptibility of a substance at an … [NEET 2003]

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Things to Remember

• Paramagnetism is magnetism where some materials are weakly attracted by an externally applied magnetic field.
• Paramagnetic materials have an unpaired electron in their valence shell.
• Paramagnetic materials are weakly attracted to a magnetic field.
• Curie's law states that magnetism is inversely proportional to temperature.
• Curie-Wiess law is derived from Curie's law.
• Ferromagnetic materials become paramagnetic materials when heated above Curie's temperature.
• Paramagnetic materials have a magnetic permeability greater than or equal to one.
• The unpaired electrons in the atoms of paramagnetic materials have an incessant dipole moment.
• The diamagnetic materials have paired electrons in their outer shell.

Read More: NCERT Solutions for Magnetism and Matter