Continuous-action or permanent magnets, in contrast toelectromagnets have the advantage that their magnetic field does not continuously need to be regenerated by a flow of electrical current but instead is able to sustain flux on a lasting basis. To achieve this, magnetizable material such as iron, nickel or cobalt needs to be exposed to a magnetic field and this leads to permanent static magnetization. All alloys from which permanent magnets can be manufactured share in common a hysteresis curve that extends across a large surface area.
Having said that, permanent magnets can also be demagnetized at an early stage, i.e. prematurely, if they are exposed to a strong opposing field or to heating action, i.e. to an increase in temperature. Even a diminishing reciprocal magnetic field can trigger this process.
The field lines in a permanent magnet, from the point they enter the South pole, describe an arc-shaped track towards the North pole, where they re-emerge.