Magnetism · Concept (Overview)

Magnetism

Reading time: 9 minConfidence: HighLast verified: August 2026

Magnetism in solids arises from the magnetic moments carried by electrons (from both their intrinsic spin and their orbital motion around atomic nuclei) and the various ways these countless individual moments respond to an applied magnetic field or spontaneously align with one another — producing behaviours ranging from weak repulsion (diamagnetism) to strong, persistent alignment (ferromagnetism).

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One sentence that captures itEvery electron is a tiny magnet, thanks to its intrinsic spin and its orbital motion around the nucleus — whether a material as a whole ends up magnetic, and how strongly, comes down to how all those countless tiny individual electron magnets end up arranged relative to each other.

At the most fundamental level, every electron behaves like an extremely small magnet, possessing a magnetic moment arising both from its intrinsic quantum spin and from its orbital motion around the atomic nucleus. In most materials, these countless individual electron magnetic moments point in essentially random directions, or cancel out in pairs (as required by the Pauli exclusion principle for electrons occupying the same orbital with opposite spins), leaving the material with no significant overall magnetism.

But in certain materials and under certain conditions, these individual magnetic moments can respond collectively to an applied magnetic field, or even spontaneously align with each other without any external field at all — producing the range of distinct magnetic behaviours (diamagnetism, paramagnetism, ferromagnetism, antiferromagnetism, and others) that condensed matter physics classifies and explains.

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Real-world exampleA common refrigerator magnet is ferromagnetic — its electron magnetic moments are locked into strong, spontaneous parallel alignment by the quantum mechanical exchange interaction, producing a substantial, permanent magnetic field with no need for any external field to sustain it, unlike the much weaker and field-dependent magnetism found in most other materials.

Type	Response to field	Typical strength	Example material
Diamagnetism	Weakly repelled	Very weak	Bismuth, water, most organic materials
Paramagnetism	Weakly attracted	Weak, field-dependent	Aluminium, oxygen gas
Ferromagnetism	Strongly attracted; can be permanently magnetised	Strong, persists without field	Iron, cobalt, nickel

Common mistake — Commonly ConfusedDiamagnetism is a property of essentially all materials, not a rare or special phenomenon — every material has some diamagnetic response, arising from the way applied magnetic fields perturb orbiting electrons' motion (via Lenz's-law-like induced currents at the atomic scale). It's usually simply too weak to notice in materials that also have stronger paramagnetic or ferromagnetic contributions, which is why diamagnetism is typically only directly observed and discussed in materials, like bismuth or water, that lack these stronger competing effects.

Deep Dive

Primary sourceHeisenberg, W. (1928). "Zur Theorie des Ferromagnetismus." Zeitschrift für Physik, 49(9–10), 619–636.

Werner Heisenberg's 1928 paper provided the first successful quantum mechanical explanation for ferromagnetism, identifying the crucial role of the exchange interaction — a purely quantum mechanical effect (with no classical analogue) arising from the combination of the Pauli exclusion principle and electrostatic repulsion between electrons, which can make it energetically favourable for neighbouring atoms' unpaired electron spins to align in parallel. Without this quantum exchange effect, ordinary magnetic dipole-dipole interactions between atoms are actually far too weak to explain the strong, persistent magnetism observed in materials like iron — a puzzle that classical physics could not resolve.

Antiferromagnetism and the Curie/Néel temperatures: Not all quantum exchange interactions favour parallel alignment — in antiferromagnetic materials, the exchange interaction instead favours neighbouring spins aligning in opposite (antiparallel) directions, producing a material with no net macroscopic magnetisation despite an underlying, highly ordered magnetic structure. Both ferromagnetic and antiferromagnetic order are disrupted by sufficient thermal energy: ferromagnets lose their spontaneous magnetisation above a characteristic Curie temperature (named after Pierre Curie, who studied this transition), while antiferromagnets lose their ordered antiparallel arrangement above a corresponding Néel temperature — both transitions are examples of continuous (second-order) phase transitions, extensively studied as prototypical examples in the broader theory of critical phenomena.

Modern data storage technology — hard disk drives, and historically, magnetic tape — relies directly on controlled, localised regions of ferromagnetic alignment (magnetic domains, see the Codex's forthcoming Magnetic Domains entry) to encode binary information, making the quantum mechanical exchange interaction, first properly explained by Heisenberg in 1928, one of condensed matter physics' most economically significant discoveries.

Concept Relationship Map

Requires: magnetic field, quantum mechanics
Enables: ferromagnetism [PENDING FULL ENTRY], exchange interaction [PENDING FULL ENTRY], magnetic domains [PENDING FULL ENTRY]
Commonly confused with: assuming diamagnetism is rare (it's universal, just usually masked by stronger effects)

Sources

Heisenberg, W. (1928). Zeitschrift für Physik, 49(9–10), 619–636.
Kittel, C. (2004). Introduction to Solid State Physics, 8th ed. Wiley, Ch. 11–12.

Last verified: August 2026 · Source: Heisenberg (1928); Kittel (2004) · Confidence: high

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