Magnetic properties of solids in Chemistry, otherwise known as magnetism, arise 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 solids 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.
What are the Main Properties of a Magnet?
Any substance that is capable of creating an invisible magnetic field is called a magnet. The three main properties of a magnet are:
1. The attractive property- As we already know that a magnet attracts other ferromagnetic materials. This is happening because of the attractive property of a magnet.
2. The repulsive property- There are two magnetic poles in any magnet. The similar magnetic poles will attract each other while the dissimilar magnetic poles will repel each other. This repulsion is due to the repulsive property of a magnet.
3. The directive property- Everybody has seen a compass. But the fundamental reason behind its working is due to the directive property of a magnet; this property states that a freely suspended magnet will always point towards the north-south direction.
Types of Magnets
There are essentially two types of magnets that are present in the world:
1. Natural magnets- The magnets which occur naturally and have an inherently permanent magnetic field are called natural magnets. One example of a natural magnet is lodestone.
2. Artificial magnets- All the other types of magnets which are formed by electromagnetism come under artificial magnets. Artificial magnets work on the molecular theory which states that every molecule has a magnetic substance, whether it is magnetised or not.
What is a Magnetic Field?
A magnetic field is a vector field, which means that it has a specific direction of movement and strength or magnitude. It determines the magnetic impact on electric charges and currents, and other magnetic materials. A magnetic field can be obtained by passing electric charge or current and is directly proportional to the magnetic movement.
What is the Intensity of a Magnetic Field?
Simply put, a magnetic field intensity is an evaluation of how strong or weak any solid’s magnetic field is. It is denoted by H and refers to the amount of force that is induced by the unit’s north pole at any specific point in the magnetic field. The SI unit of the intensity of a magnetic field is equivalent to Ampere/meter or A/m. The direction of the magnetic field is usually derived by drawing a tangent on the line of forces that are experienced at a given point.
Some of the common concepts that are derived from understanding the intensity of a magnetic field are:
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Magnetic Pole Strength- It is denoted by the symbol p and refers to the quantity of the strength of the poles of any bar magnet.
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Magnetic Movement- A solid experiences a certain amount of rotational force in an external magnetic field. The measurement of this quantity is known as the magnetic movement. Therefore, it is possible to find the magnetic movement in any loop of an electric current or an electron that revolves around an atom.
What are Some Common Applications of an Electromagnet?
Electromagnets are used worldwide in various electronic products- both big and small.
Some of the applications of electromagnets are discussed below-
1. Everyday home uses- From doorbells to induction cookers, almost all the appliances that are used in the everyday working of a housework under the principle of electromagnetism
2. Medical field applications- Electromagnetism is exclusively used to build an MRI machine, which uses electromagnets to perform scans of the human as well as animal bodies. MRI, hence, stands for Magnetic Resonance Imaging.
3. Used in computer hard wares and other memory storing devices- All the information that is stored in a computer, laptop, phone, or any kind of hard disk is stored in the form of bytes or bits that are electromagnets. The computer hardware has a magnetic tape that works on the fundamentals of electromagnetism.
4. Used in various communication devices- The everyday mobiles and telephones that we use to perform long-distance communication with other people work on the principle of electromagnetism- through the interaction between different signals and electromagnetic pulses.
Classification of Magnetism
Different solids can be classified into several groups depending on their magnetic properties. The classification can be given as:
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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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.
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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These substances possess a net zero 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.
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, and 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 are considered. Magnetism originates from the rotating and orbital motions of the electrons. Just like the current flowing through solenoids generates 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 the 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 the case of transition elements with not fully occupied d- orbital and rare earth elements with not fully occupied f- orbital magnetic moments due to spin rotation appears.