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Magnetism

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"Magnetic" redirects here. For other uses, see Magnetic (disambiguation) and Magnetism (disambiguation).

A magnetic quadrupole

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Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Every material is influenced to some extent by a magnetic field. The most familiar effect is on permanent magnets, which have persistent magnetic moments caused by ferromagnetism. The prefix ferro- refers to iron, because permanent magnetism was first observed in a form of natural iron ore called magnetite, Fe₃O₄. Most materials do not have permanent moments. Some are attracted to a magnetic field (paramagnetism); others are repulsed by a magnetic field (diamagnetism); others have a more complex relationship with an applied magnetic field (spin glass behavior and antiferromagnetism). Substances that are negligibly affected by magnetic fields are known as non-magnetic substances. These include copper, aluminium, gases, and plastic. Pure oxygen exhibits magnetic properties when cooled to a liquid state.
The magnetic state (or magnetic phase) of a material depends on temperature and other variables such as pressure and the applied magnetic field. A material may exhibit more than one form of magnetism as these variables change.

Contents

• 1 History
• 2 Sources of magnetism
• 3 Materials
  • 3.1 Diamagnetism
  • 3.2 Paramagnetism
  • 3.3 Ferromagnetism
    • 3.3.1 Magnetic domains
  • 3.4 Antiferromagnetism
  • 3.5 Ferrimagnetism
  • 3.6 Superparamagnetism
  • 3.7 Other types of magnetism
• 4 Electromagnet
• 5 Magnetism, electricity, and special relativity
• 6 Magnetic fields in a material
• 7 Magnetic force
• 8 Magnetic dipoles
  • 8.1 Magnetic monopoles
• 9 Quantum-mechanical origin of magnetism
• 10 Units
  • 10.1 SI
  • 10.2 Other
• 11 Living things
• 12 See also
• 13 References
• 14 Further reading
• 15 External links

History

Main article: History of electromagnetism

Drawing of a medical treatment using magnetic brushes. Charles Jacque 1843, France.

Aristotle attributed the first of what could be called a scientific discussion on magnetism to Thales of Miletus, who lived from about 625 BC to about 545 BC.^[1] Around the same time, in ancient India, the Indian surgeon Sushruta was the first to make use of the magnet for surgical purposes.^[2]
In ancient China, the earliest literary reference to magnetism lies in a 4th-century BC book named after its author, The Master of Demon Valley.^[3] The 2nd-century BC annals, Lüshi Chunqiu, also notes: "The lodestone makes iron approach, or it attracts it."^[4] The earliest mention of the attraction of a needle is in a 1st-century work Lunheng (Balanced Inquiries): "A lodestone attracts a needle."^[5] The 11th-century Chinese scientist Shen Kuo was the first person to write – in the Dream Pool Essays – of the magnetic needle compass and that it improved the accuracy of navigation by employing the astronomical concept of true north. By the 12th century the Chinese were known to use the lodestone compass for navigation. They sculpted a directional spoon from lodestone in such a way that the handle of the spoon always pointed south.

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Ditulis Unknown — Monday 25 July 2016 — 2 Comments — Fisika