Magnetic hysteresis occurs when ferromagnetic materials retain magnetization after field removal. Field strength-magnetization relationship is not linear in ferromagnetic materials. Magnetization follows initial curve then approaches saturation. Main loop width equals twice material's coercivity
Saturation occurs when external magnetic field cannot increase material magnetization further. Different ferromagnetic materials have varying saturation levels. Saturation is most clearly seen as right-bending magnetization curve. Above saturation, magnetization continues at paramagnetic rate
Ferromagnetism is the strongest type of material magnetism. Materials with significant magnetic permeability can form permanent magnets. Three other types exist: paramagnetism, diamagnetism, and antiferromagnetism
Ancient people used lodestones, the word "magnet" comes from Greek "magnesian stone". Thales investigated magnetism around 625-545 BCE. Compass navigation began in China in 11th century, Europe in 1187. Ørsted discovered magnetic fields around live wires in 1819
Natural ferromagnets include lodestone and iron discovered over 2,000 years ago. Iron, cobalt, nickel, and their alloys are commonly used ferromagnets. Ferromagnets are used in electric motors, transformers, and everyday devices
Paperclip magnet can be made by rubbing small metal with refrigerator magnet. Test magnet by moving paperclip 50 times quickly in same direction. Experiment with different paperclip sizes and metals to find strongest magnet