Magnetic Properties of Solids

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Magnetic Properties of Solids in Class 12

Magnetic properties of solids in Chemistry, otherwise known as magnetism arises from the magnetic dipole moment in solids. This magnetic dipole moment in magnetic materials appears from the spinning of electrons in its axis and orbital motion around the nucleus of the atom. The magnetic properties of solid are observed due to the magnetic fields created by electrons’ magnetic moment and electric currents. The magnetic property of solids is only one aspect of electromagnetism. The small charge of an electron generates a magnetic field along its axis. The magnetic moment is produced due to the angular momentum of the spinning motion of the electron.


Classification of Magnetism

Different solids can be classified into several groups depending on their magnetic properties. The classification can be given as:

  • Diamagnetic Substances: 

This category of substances are solids that are weakly repelled by magnets. The materials with diamagnetism have all paired electrons. Hence, the magnetic dipole moment is cancelled.  Examples of diamagnetic substances are H2O, TiO2, NaCl, and V2O5, etc. These substances have a small magnetic dipole moment which is opposite to the magnetic field.

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  • Ferromagnetic Substances: 

These substances are strongly attracted by the magnetic field. They can also be permanently magnetized. The ions of ferromagnetic substances group together in small regions to act like a tiny magnet. This small magnetic region is called a domain. Upon application of a magnetic field, these domains are oriented in the same directions. Even after the removal of the magnetic field, the domains remain oriented to form permanent magnets. Some examples are Fe, Co, Ni, etc.

  • Paramagnetic Substances: 

Solid substances that are weakly attracted by a magnetic field are called paramagnetic substances. They are magnetized in the same direction as the magnetic field. These are not permanent magnets. Paramagnetism is caused when one or more unpaired electrons are attracted by the magnetic field. So, they are temporary magnets. Some examples of paramagnetic substances are O2, Cu2+, VO, VO2, CuO and TiO, etc.

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  • Antiferromagnetic Substances: 

These substances possess a net 0 magnetic moment. However, they have the same domains as ferromagnetic substances. Since these domains are oppositely oriented they cancel out each other and result in zero magnetic moments. MnO, V2O are examples of antiferromagnetic substances.

  • Ferrimagnetic Substances: 

These substances possess little magnetic moment. Here, the magnetic moment of the domains of the substances is aligned in parallel and antiparallel directions in unequal numbers. The examples are magnetite and ferrites.


Electrical and Magnetic Properties of Solids

As stated earlier, the electrical and magnetic properties of solids are two different aspects of a single phenomenon, known as electromagnetism. Solids all have different electrical conductivities. Conductivity is the property of an object to conduct electricity. Other such electric properties of solids include resistivity, capacitance, and impedance. Metals and alloys are great electric conductors, whereas ceramics and glasses are good insulators. Semiconductors have both electrons and holes in them to contribute to current. Materials such as aluminium, tin, metal alloys, heavily doped semiconductors also exhibit superconductivity at low temperatures. 


The Origin of Magnetic Properties in Solids

To explain the origin of magnetic properties in solids, the electrons orbiting inside atoms of the object is considered. The magnetism origins from the rotating and orbital motions of the electrons. Just like the current flowing through solenoids generate a magnetic field, the charge of an electron causes a magnetic moment from the spin rotation of the electron. This magnetic moment is known as Bohr magneton(µB), the smallest unit of the magnetic moment of solids. The value of Bohr magneton is equal to 9.27 × 10-27 A m2. Since only two electrons with up and down spins occupy an orbit, the magnetic moment generated is cancelled out. Only in case of the transition elements with not fully occupied d- orbit and rare earth element with not fully occupied p- orbit magnetic moment due to spin rotation appears.  

FAQ (Frequently Asked Questions)

Q1. What is an Electromagnet?

An electromagnet is an instrument that has a magnetic core, the core is surrounded by a coil, known as a solenoid. When an electric current is passed through the coil, the core is magnetized. The generated magnetic field has similar field lines as those of a magnet and the orientation can be determined by the right-hand rule. The magnetic field is directly proportional to the number of loops of the coil around the core, and the cross-section of each loop. The magnetic field of an electromagnet can be controlled and changed by the amount of electric current passing through the winding. However, unlike permanent magnets, an electromagnet needs a supply of electric current to maintain the magnetic field. 

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Q2. Define Permanent Magnet. What are their Uses?

A magnet made up of material that can be magnetized and create a magnetic field, is called a permanent magnet.  The magnetization in these magnets can not be destroyed even if handled roughly. 

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They have many uses, such as:

  1. Videotapes contain magnetic tape, the magnetic coating on the tape encodes sound and information on the video. Floppy disks, hard disks also record data on magnetic coating.

  2. ATM, Credit, and Debit cards have a thin magnetic strip to encode information.

  3. Electric motors and generators use a combination of an electromagnet and permanent magnet, where they convert electric energy to mechanical energy. 

  4. It is used in compasses that have a magnetic pointer to align with the earth’s magnetic field. 

  5. They are also used in scrap and salvage operations to find magnetic metals from non-magnetic substances.