Magnets that can maintain their magnetism for a long time is called permanent magnet, such as natural magnets and artificial magnets and so on. In addition to permanent magnets, there are also electromagnets that need to be energized to be magnetic.
Permanent magnets are not easily demagnetized or magnetized. However, if the permanent magnet is heated above the curie temperature, or placed in an environment with a reverse high magnetic field strength, its magnetism will also decrease or disappear.
Some magnets are brittle and may crack at high temperatures. The maximum operating temperature of alnico magnets exceeds 540 °C (1,000 °F), samarium cobalt magnets and ferrites are about 300 °C (570 °F), neodymium magnets and soft magnets are about 140 °C (280 °F) F), but the actual value will still vary according to the grain of the material.
Most of the materials used as magnetizers and electromagnets are soft magnets. The polarity of the permanent magnet does not change, but the polarity of the soft magnet changes with the polarity of the applied magnetic field. They can all attract ferrous objects, and we call this property magnetism.