[Physics Class Notes] on Magnetic Classification of Materials Pdf for Exam

Every substance shows some kind of magnetic behaviour at a time. This magnetic behaviour is shown because these substances are made up of charged particles like electrons and protons. It is how the electrons are arranged by themselves in the atoms and how groups of these atoms behave that tell us the magnetic properties of the material. These atoms (or the group of atoms) as a result become a magnetic dipole or a minibar magnet that can align according to the magnetic field that has been applied. The resultant effect of these dipoles determines the magnetic properties of the magnetic materials.

Types of Magnetic Materials

To study the magnetic properties of magnetic materials, we generally keep the material in a uniform magnetic field, and then the magnetic field is varied. Based on their behaviour, the magnetic materials can be classified into three major types:

They are barely magnetized when they are placed in the presence of a magnetic field. Magnetic dipoles here tend to align in opposition to the applied field. As a result, an internal magnetic field is produced by them that opposes the applied field and the substances tend to repel the external force around them.

Some examples of diamagnetic materials are silver, mercury, lead, carbon (graphite and diamond), and copper.

In paramagnetic materials, the magnetic dipoles present in them tend to align along the applied magnetic field and hence reinforcing the applied magnetic field. Paramagnetic substances are attracted by a magnet if it applies a considerable amount of strong field. It is to be kept in mind that such materials are still feebly magnetized and the magnetization will disappear right when the external field is removed. Madame Curie, a very famous Nobel laureate, discovered the magnetization (M) of such materials and this is dependent on the external magnetic field (B) and temperature T by the equation

M=CBT

Here, C stands for Curie constant.

A few examples of paramagnetic materials are as follows: Tungsten, Caesium, Aluminum, Lithium, Magnesium, and Sodium.

These materials produce a very strong magnetism in the direction of the magnetic field when a magnetic field is applied to it. A domain is a tiny area in ferromagnetic materials with a specific overall spin orientation produced due to quantum mechanical effort. This effect is exchange interaction, that is when some unpaired electrons are under consideration, they interact with each other between two atoms, and they line up themselves in a small region in the direction of the magnetic field. This mechanism of ferromagnetic materials is known as ferromagnetism.

Some examples of ferromagnetic materials are cobalt, iron, nickel, gadolinium, and terbium.

Is Water Diamagnetic in Nature?

Water is known to be a diamagnetic material. Diamagnetic materials are the ones that contain only electron pairs. However, a molecule of water has two bonding pairs of electrons between the hydrogen and oxygen atoms and two lone pairs of electrons present in the oxygen atom. Paramagnetic molecules are said to have at least one pair of unpaired electrons. This occurs when the molecules have an odd number of electrons (like in nitric oxide). It also happens when there are even numbers (like in oxygen) in some molecules. We have seen that water repels the magnet. This happens because whenever there is a presence of any magnetic field near water, a new magnetic field is created by the water itself, thus repelling the magnet. This is called diamagnetism. 

Curie Temperature

Curie Temperature or Curie Point is the temperature at which a particular magnetic substance undergoes a steep change in its magnetic properties. In the case of rocks and minerals, remnant magnetism appears below the Curie temperature for the common mineral magnetite. This temperature is named after the French physicist Pierre Curie, who discovered the laws that relate some magnetic properties to change in temperature in 1895. Below the Curie temperature, atoms that behave as tiny magnets tend to spontaneously align themselves in certain magnetic materials. In ferromagnetic substances, such as pure iron, the atomic magnets are oriented within each microscopic region in the exact direction, so that their magnetic fields strengthen each other. 

Raising the temperature to the Curie temperature to ferromagnetic, antiferromagnetic, and ferrimagnetic substances entirely disrupts the various spontaneous arrangements, and only a weak kind of more general magnetic behaviour, known as paramagnetism, stays. Cobalt has one of the highest Curie points. When the temperature of these materials is brought below their Curie points, magnetic atoms spontaneously realign themselves so that the ferromagnetism, antiferromagnetism, or ferromagnetism revives.

 

Applications of Magnetism

• There are many real-life applications of magnetism as magnets are used in the majority of products and mechanisms involved, also they play a vital role in many of these such as electromagnets are used in motors and generators, as well as in power supplies that convert electrical energy from a wall outlet into direct current energy for a wide range of variety of electronic devices present around us. Also, there are many important applications of magnetism in the field medical field such as in MRI (magnetic resonance imaging) devices that are now widely used in hospitals and medical centres where high field superconducting magnets (where superconducting coils generate the magnetic field) provide the magnetic field.

• Permanent magnets are made of magnetic materials that are difficult to demagnetize. Loudspeakers, earphones, electric meters, and small motors all use permanent magnets. A loudspeaker is made up of a wire that transmits an alternating current. When the wire is in the permanent magnet’s magnetic field, it is subjected to a force that causes the surrounding air to alternately compress and rarely resulting in a sound wave.

• Computers which are a very important part of the modern world also comprise magnetic mechanisms such as storage devices and magnetic recording in computers, as well as audio and video systems or machines, are some of the more widely used applications of magnetism. The devices with magnetic storage work majorly on the basis of two stable magnetic states, which are represented by the binary numbers 0 and 1. 

• A write-head can digitally write in or store data on a floppy disk’s dozens of tracks, which can then be accessed or read using a read-head. A write-head generates a strong local magnetic field in the region where the disk’s storage track passes. As the disk passes over the read-head, it detects stray magnetic flux from the storage track. The magnetic stripe on the back of plastic debit and credit cards is another example of digital magnetic storage and reading. The magnetic strip contains identification data that can be accessed via an automatic teller machine, for example.