<P> Magnetic imaging devices (e.g. MRIs) generate enormous magnetic fields, and therefore rooms intended to hold them exclude ferrous metals . Bringing objects made of ferrous metals (such as oxygen canisters) into such a room creates a severe safety risk, as those objects may be powerfully thrown about by the intense magnetic fields . </P> <P> Ferromagnetic materials can be magnetized in the following ways: </P> <Ul> <Li> Heating the object above its Curie temperature, allowing it to cool in a magnetic field and hammering it as it cools . This is the most effective method and is similar to the industrial processes used to create permanent magnets . </Li> <Li> Placing the item in an external magnetic field will result in the item retaining some of the magnetism on removal . Vibration has been shown to increase the effect . Ferrous materials aligned with the Earth's magnetic field that are subject to vibration (e.g., frame of a conveyor) have been shown to acquire significant residual magnetism . Likewise, striking a steel nail held by fingers in a N-S direction with a hammer will temporarily magnetize the nail . </Li> <Li> Stroking: An existing magnet is moved from one end of the item to the other repeatedly in the same direction . </Li> <Li> Electric Current: Applying an electric current via a coil can get all of the domains to line up . Once all of the domains are lined up, increasing the current will not increase the strength of the magnetic field . </Li> </Ul> <Li> Heating the object above its Curie temperature, allowing it to cool in a magnetic field and hammering it as it cools . This is the most effective method and is similar to the industrial processes used to create permanent magnets . </Li>

How can you turn an iron or steel object into a magnet
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