Magnetic Properties of Solids

We are all aware of magnets, and you also probably know the metals that are magnetic. But did you know that the magnetic property of a solid is due to its atomic structure? Let us take a look at the different types of magnetic solids.

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Magnetic Property of Solids

The magnetic properties of a solid are the result of the magnetic property of the atoms or ions of these solids. More specifically the magnetism and magnetization of a solid will depend on the movement of electrons in an atom. It can thus be said that each electron of an atom behaves like a magnet, lending the whole solid its magnetic property.

This magnetic behaviour of the electrons of an atom is due to the movement patterns. They have specifically two types of movements,

• Electrons revolve around the nucleus of the atom
• Electrons also spin on their own axis, spins in opposite sides are labelled with + and – signs.

These two motions of the electrons give the atom and the substance their magnetic power. These constant motions make an electric field around the electrons, almost like a loop of current which lends it its magnetic property. On the basis of their magnetic properties, solids can be classified into five categories. Let us take a look.

Paramagnetic

These substances are weakly magnetized in an external magnetic field. The direction is the same direction of the magnetic field. So they gain a net magnetization When we remove the paramagnetic substance from the field, the alignment of electrons is interrupted and the substance will lose its magnetic property. Thus paramagnetic substances are not permanent magnets.

Paramagnetism is due to at least one pair of unpaired electrons in its orbit shell which get magnetized in the magnetic field. Some common examples are O2, Cu2 etc. These paramagnetic substances find a variety of applications in electronics.

Browse more Topics under The Solid State

• General Introduction
• Crystalline and Amorphous Solids
• Space Lattice or Crystal Lattice and Unit Cell
• Number of Particles in Unit Cells
• Close Packing in Crystals
• Tetrahedral and Octahedral Voids
• Radius Ratio Rules
• Density of a Cubic Crystal
• Imperfections or Defects in a Solid
• Electrical Properties of Solids

Diamagnetic

Just like paramagnetism, in diamagnetism too the substances are magnetized in an external magnetic field. But diamagnetic solids are repelled in the field. The magnetic property effected in them is in the opposite direction of the magnetic fields and thus they have a repulsive force.

In diamagnetic substances, all electrons in their last shell are paired, there are no valence electrons. This is the reason that the magnetic moment of their atoms is nearly zero. Examples are substances like Sodium Chloride, Benzene etc. Being such bad conductors, we use them as insulators.

Ferromagnetic

Now, these solids are strongly magnetized when we place them in an external magnetic field. Besides the very strong attraction forces, these solids can actually be magnetized permanently. This means that even when the external magnetic fields are removed the solids will retain their magnetic properties.

It is a widely believed theory that the ferromagnetic structures have certain special characteristics. They have what we call “domains’ which is a special grouping of metal ions. Each domain is similar to a small magnet. In an electromagnetic field, these domains rearrange themselves and align themselves with the magnetic field. In a non-magnetized metal, these domains are randomly arranged and it cancels out their magnetic properties.

The examples of ferromagnetic solids include Cobalt, Nickel, Chromium Oxide etc. And they have widespread industrial and every day uses.

Antiferromagnetic

In antiferromagnetism, the domain structures of the solid are very similar to those of ferromagnetic solids. But here the domains are oppositely oriented. This means they cancel out each other’s magnetism.

Ferrimagnetic

These substances occur when magnetic moments are aligned in both directions (parallel as well as anti-parallel) but in unequal numbers. These are weakly attracted to magnetic fields. Also on heating, these substances will lose their ferrimagnetism altogether. Examples are magnetite and ferrites of Zinc and Magnesium.

Solved Question for You

Q: The temperature at which the domain structure gets destroyed and ferromagnetic substance is converted into the paramagnetic substance are called as :

1. critical temperature
2. saturation temperature
3. curie temperature
4. Kraft temperature

Ans: The correct option is “C”. Curie temperature or Curie point is the temperature at which certain materials lose their permanent magnetic properties, to be replaced by induced magnetism. The Curie temperature is named after Pierre Curie, who showed that magnetism was lost at a critical temperature. And ferromagnetic substances get converted into paramagnetic substances