The polarity of a magnet defines its orientation: which end is the North pole and which is the South pole. This characteristic is responsible for the forces of attraction and repulsion between magnets. Reversing the polarity of a temporary magnet is simple, but changing a permanent magnet is difficult, requiring specific conditions and specialized, high-power equipment. Achieving this reversal means overcoming the magnet’s inherent stability and forcing a complete reorientation of its internal magnetic structure.
The Fundamentals of Polarity
Magnetic polarity originates at the atomic level within ferromagnetic materials like iron, nickel, and cobalt. Electrons spinning around atoms create tiny magnetic fields, or magnetic moments. In ferromagnetic substances, groups of atoms align these moments to form regions called magnetic domains, unlike most materials where these moments cancel out.
Within a single magnetic domain, the magnetization is uniform. The overall polarity of a permanent magnet is determined by the collective alignment of all these domains. When the material is magnetized, nearly all domains align in one direction, creating a strong, stable external field. The magnetic field lines flow from the North pole to the South pole outside the magnet, establishing the defined polarity.
Applying an Opposing Magnetic Field
The most direct way to reverse a permanent magnet’s polarity is to subject it to an opposing magnetic field stronger than its own internal resistance. This resistance is known as coercivity. To successfully reverse the magnet, the external field must exceed the magnet’s coercivity value to neutralize the existing field.
The external field is typically generated by specialized equipment like a pulse magnetizer or a powerful industrial solenoid. These devices deliver an extremely intense, short-duration magnetic pulse to the material. The required opposing field strength depends heavily on the magnet’s material; for high-strength neodymium magnets, fields of up to 4 Tesla or more may be necessary. This process forces the magnetic domains to flip their alignment by 180 degrees, establishing the new poles.
The energy required to flip the polarity is considerable, often exceeding the energy initially used to magnetize it. The industrial equipment needed to safely generate these powerful fields is not available to the average person. Attempting this reversal without specialized gear is ineffective and potentially hazardous.
Demagnetization Through Heating
An indirect method for reversing polarity involves a two-step process: first demagnetizing the material completely, then remagnetizing it in the opposite direction. Demagnetization is achieved by heating the magnet above a specific temperature known as the Curie temperature. This is the temperature at which a material loses its permanent magnetic properties.
When a ferromagnetic material reaches its Curie temperature, the thermal energy disrupts the alignment of the magnetic domains. The organized magnetic moments become randomly disordered, and the material ceases to be ferromagnetic, becoming paramagnetic with no permanent external field. For example, the Curie temperature of magnetite is around 585 °C (1,085 °F).
Once the magnet cools below its Curie point, its magnetic moments spontaneously realign. To achieve polarity reversal, the hot, demagnetized material must be cooled while exposed to a weak external magnetic field oriented in the new direction. As the material cools, the domains “freeze” into alignment with the new field, permanently setting the reversed polarity.
Reversing Electromagnets
Reversing the polarity of an electromagnet is significantly simpler than reversing permanent magnets. An electromagnet is a temporary magnet created by running an electrical current through a coiled wire, and the magnetic field exists only while the current is flowing.
The polarity is instantly reversed by changing the direction of the electrical current in the coil. This is typically done by switching the connections of the coil’s leads to the power supply, reversing the positive and negative terminals. Switching the current direction causes the magnetic field lines to reverse their flow, immediately flipping the North and South poles. Devices like an H-bridge circuit or a double pole double throw switch can achieve this rapid reversal electronically.