Permanentmagnete

Permanentmagnete are materials that generate a persistent magnetic field without external energy input. They retain their magnetization after being exposed to a magnetic field, although their strength can decrease with temperature or opposing fields. The main families are hard ferrites, Alnico, and rare‑earth magnets (neodymium–iron–boron NdFeB and samarium–cobalt SmCo).

Key properties include the remanent flux density, coercivity, and the energy product BHmax, which quantify how much magnetic field the material can supply. NdFeB magnets offer the highest energy density, followed by SmCo, ferrites, and Alnico. Temperature stability varies and excessive heat can demagnetize magnets with lower coercivity.

Manufacture and magnetization: Ferrites are ceramic oxides; Alnico is a metallic alloy; NdFeB and SmCo are produced as sintered or bonded magnets. They are magnetized in strong external fields to saturation and then cut or formed into shapes. Corrosion resistance is often improved with coatings such as nickel, zinc, or epoxy. NdFeB magnets are particularly prone to oxidation and often require protective coatings. They are also relatively brittle, requiring careful handling during machining and assembly.

Applications include electric machines (motors and generators), magnetic separation, loudspeakers and headphones, sensors, magnets for medical devices, and various holding and latching devices. Permanent magnets enable energy-efficient, compact designs but require design considerations for temperature, demagnetization, and mechanical stress.

History: Natural magnets have been known for centuries; modern permanent magnets emerged in the 20th century with Alnico and were significantly advanced by NdFeB and SmCo, expanding capabilities for compact, powerful magnetic devices.