Magnetism

- Overview

The history of magnetism dates back before 600 BC, but it wasn't until the twentieth century that scientists began to understand it and develop technology based on this understanding.  

The Englishman William Gilbert (William Gilbert, 1540-1603) was the first person to use scientific methods to systematically study magnetic phenomena. He also discovered that the Earth itself is a weak magnet. German Carl Friedrich Gauss (1777-1855) conducted early theoretical studies of the nature of Earth's magnetism

Magnetism is the force created by the movement of electrons within atoms in matter. Magnetism and electricity represent different aspects of the electromagnetic force, which is part of the fundamental electroweak force of nature. 

The region of space traversed by imaginary magnetic field lines describes the magnetic field. The strength of a magnetic field is determined by the number of lines of force per unit area of space. 

Magnetic fields are created on a large scale by passing electric current through magnetic metals, or magnetized materials called magnets. 

Elemental metals—iron, cobalt, nickel, and their solid solutions or alloys with related metallic elements—are typical materials that respond strongly to magnetic fields. 

Unlike the fundamental gravitational field that is ubiquitous, the magnetic force field inside a magnetized body such as a bar magnet is polarized, that is, the magnetic field is strongest and has opposite signs at the two ends, or poles, of the magnet.

- Magnetizing

Magnetic fields are produced by electric currents. Permanent magnets are the result of a "magnetizing current" flowing inside the material. The magnetization current in a material is the result of the orbital motion and spin of electrons. 

Electrons have an inherent property called spin. Because they have spin, they have a magnetic moment, similar to a small current loop. Electrons themselves are like tiny magnets. 

If you choose an axis, an electron's magnetic moment can be parallel or antiparallel to that axis. In atoms, electrons are arranged in orbitals. 

An orbital electron can have an extra magnetic moment, similar to that of a tiny current loop. If all the magnetic moments of the electrons in the atom do not completely cancel out, the atom will work like a small magnet.  

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- Demagnetizing

To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on the coercivity of the corresponding material. "Hard" materials have high coercivity, while "soft" materials have low coercivity. 

The overall strength of a magnet is measured by its magnetic moment, or by the total magnetic flux it produces. The local magnetic strength in a material is measured by its magnetization.

- Electromagnet 

An electromagnet is made of a coil that acts as a magnet when current is passed through it, but ceases to be a magnet when the current stops. Typically, the coil is wound around a magnetic core of a "soft" ferromagnetic material, such as mild steel, which greatly enhances the magnetic field generated by the coil.

- Diamagnetism

When any material is placed in a magnetic field, its atoms acquire an induced magnetic moment that points in the opposite direction to the external field. The material becomes magnetic. This is called diamagnetism. 

The diamagnetic field generated by the material is the opposite of the external magnetic field, but except for superconductors, this diamagnetic field is very weak. 

If the atoms of a material have no magnetic moment themselves, then diamagnetism is the only magnetic property of the material, and the material is called diamagnetism. Copper is one such material.

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