--- title: "Magnetisation: Diamagnetism, Paramagnetism and Ferromagnetism" description: "Magnetisation is magnetic moment per unit volume. Diamagnetic and paramagnetic materials usually respond weakly in opposite directions. Below its Curie temperature, a ferromagnet has ordered domains a" canonical: https://lightmysky.com/learn/science/magnetisation-diamagnetism-paramagnetism-and-ferromagnetism-mt_1apyQ1_1gg source: https://lightmysky.com/learn/science/magnetisation-diamagnetism-paramagnetism-and-ferromagnetism-mt_1apyQ1_1gg.md retrieved: 2026-11-12 --- > **Agent view.** This is the Markdown twin of the page, for tools and assistants. > When to use this site, and the call that answers each job: https://lightmysky.com/agent-instructions.md > API description (OpenAPI 3.1): https://lightmysky.com/openapi.json · Authentication: https://lightmysky.com/auth.md > Pricing: https://lightmysky.com/pricing.md · Catalog: https://lightmysky.com/llms.txt · Full catalog: https://lightmysky.com/llms-full.txt > Every machine-readable file on this domain: https://lightmysky.com/.well-known/ai-catalog.json > Ask for Markdown with `Accept: text/markdown`, a `.md` address, or `?mode=agent`. # Magnetisation: Diamagnetism, Paramagnetism and Ferromagnetism Magnetisation is magnetic moment per unit volume. Diamagnetic and paramagnetic materials usually respond weakly in opposite directions. Below its Curie temperature, a ferromagnet has ordered domains and can retain magnetisation after an applied field is removed. Differently directed domains can also cancel, leaving a sample unmagnetised. Subject: Science · Area: Electricity & Magnetism · Ages 20 to 21 Page: https://lightmysky.com/learn/science/magnetisation-diamagnetism-paramagnetism-and-ferromagnetism-mt_1apyQ1_1gg ## Ready when they can - Classifies diamagnetic, local-moment paramagnetic and ferromagnetic responses using induced opposition, partial alignment and cooperative domain order - Explains why an iron core can greatly increase a solenoid's field while a copper core changes it only slightly at the same coil current - Interprets B-H loop area and zero crossings, relating them to hysteresis loss per volume per complete cycle and B-coercivity ## Lesson: Magnetisation and magnetic history Magnetisation is magnetic moment per unit volume. An applied field induces an opposing diamagnetic response. Copper has a small net response of this kind. In a nonuniform field, a diamagnetic sample tends to move toward weaker-field regions. A uniform field alone does not give this translational force. Stronger effects can hide the diamagnetic contribution in other materials. In a local-moment paramagnet, atoms or ions have permanent magnetic moments. Without an applied field, the moments point in many directions, giving zero average magnetisation. A field produces partial alignment and weak attraction toward stronger-field regions. At fixed applied field, warming generally reduces the alignment because thermal motion competes with it. Exchange interactions favour parallel neighbouring moments in a ferromagnet. Below the Curie temperature, moments align within domains without an applied field. Differently directed domains can cancel. A coil field changes domain sizes and directions, increasing net magnetisation. At fixed coil current, iron can greatly increase a solenoid's field; copper slightly reduces it. Iron's response depends on field strength and magnetic history. *(drawing: Ordered domains can cancel at first. After magnetising, some net alignment may remain. Domains in a permanent magnet are not immovable.)* **Example.** To magnetise an iron or steel nail, stroke it with the same magnet pole in one direction. Lift the magnet and return through the air before repeating. An opposite contact pass can reduce net alignment. Compare how many similar paper clips the nail lifts before and after. Do not heat or strike the nail. High-temperature demonstrations require laboratory equipment and protection from burns. Above its Curie temperature, iron loses spontaneous ferromagnetic order and becomes paramagnetic. An applied field can still produce magnetisation, but removing it leaves no spontaneous magnetisation. A mechanical shock can change domain patterns and reduce a magnet's strength without destroying its underlying ferromagnetic order. On a B-H loop, B is flux density and H is magnetising field. The branches record magnetic history. The reverse H needed to reach B = 0 defines B-coercivity. For a symmetric loop, each zero crossing has magnitude HcB; their separation is 2HcB. With slow field changes and negligible eddy-current loss, loop area gives hysteresis energy lost per volume per full cycle, in J/m^3. Transformer cores reverse magnetisation repeatedly. Compare hysteresis loss at equal core volume, cycle frequency and peak B: the smaller B-H loop area gives less heating. Small coercivity often accompanies low loss, but width alone does not determine area. Eddy currents add another loss, so hysteresis alone does not predict total core heating. In the example, A loses 20 J/m^3 per full cycle and B loses 50 J/m^3. **Recap.** Diamagnetism opposes the field; paramagnetism weakly aligns. Ferromagnets have ordered domains below the Curie temperature. B-H loop area gives hysteresis loss per volume per complete cycle. *Lesson, questions and flashcards written for this dataset. Scientific background was studied in OpenStax's Magnetism in Matter and Ferromagnets and Electromagnets sections; their prose and figures are not reproduced.* ## Practice 8 questions on this page, each with its working shown. ## Needs first - [Dielectrics and the Polarisation of Matter](https://lightmysky.com/learn/science/dielectrics-and-the-polarisation-of-matter-mt_OYRr_k3IW6) - [Ampere's Law: Wires, Solenoids and Toroids](https://lightmysky.com/learn/science/amperes-law-wires-solenoids-and-toroids-mt_uTzRcSiUQ-) ## Opens up - [Critical exponents, scaling and universality](https://lightmysky.com/learn/science/critical-exponents-scaling-and-universality-mt_EaJOjyvjjj)