Permanent magnets are all around us, with the most common being our decorative refrigerator
magnets. These objects are critical components in many of the appliances and equipment we
use today, from MRI scanners to audio devices, motors, generators, security systems, and
many more. As a result, permanent magnet technology makes our lives easier and more
comfortable. Look below to know more about permanent magnets, how they work, how they
differ from electromagnets, types, and how one is made.
What is a Permanent Magnet?
Permanent magnets are objects made from materials that are magnetized, producing their own persistent magnetic field. They are made from special alloys or ferromagnetic materials such as iron, nickel, and cobalt.
Magnetic Field of a Permanent Magnet
Permanent magnets possess two poles with opposite effects, called the “north pole” and the
“south pole.” Like electrical charges, these poles have a positive and negative charges. When
similar poles are placed together, it will cause a repelling force, while different poles cause an
attractive force. Thus, permanent magnets will always possess two poles, even if they are
broken in half. Magnetic fields of permanent magnets are generated by the nucleus and electrons of the atoms that make up the material. The nucleus and electrons act like little magnets, spinning around, each having a persistent magnetic field. The electrons also produce a magnetic field as it rotates around the orbit of the nucleus. When the spins and orbits of the electrons and nucleus line up in a uniform direction, magnetism is produced.
How Permanent Magnets are made
Ferromagnetic materials like iron, cobalt, and nickel have inherent properties that allow the
spins of their nucleus and electrons to align in a uniform direction when an external magnetic
field is applied to them. Applying a very strong magnetic force causes the nucleus and electrons of these materials to permanently spin in a uniform direction, thus turning these materials into permanent magnets.
The strength of a magnet is dependent on the properties of the ferromagnetic material. For
example, magnets made from rare earth metals like Neodymium have high saturation magnetization allowing them to store greater magnetic energy, therefore stronger pulling force. Magnets that use compound metals like iron nitride permanent magnets also produce strong magnetic force due to their material having localized electrons that spin in a uniform direction.
Permanent Magnets vs. Electromagnets
While a permanent magnet is a type of magnet that has a persistent magnetic field, an electromagnet generates its magnetic field via electric currents. Electromagnets are made from wires wound into a coil.
Key Differences
Magnetic Properties – The properties of a permanent magnet are due to its magnetization
process. An electromagnet only exhibits its magnetic property when an electric current is
applied to it.
Strength – The strength of a permanent magnet is dependent on the material and cannot be
changed. Meanwhile, electromagnets can be adjusted depending on the amount of electric
current allowed to flow through them.
Loss of Magnetization – Permanent magnets can lose their magnetization when heated to
specific maximum temperatures as it causes the electrons and nucleus to spin in different
directions. Electromagnets only lose their magnetic properties when their electric current is
turned off.
Polarity – The polarity of electromagnets depends on the direction of flow of the electric current
passing through it. On the other hand, the poles of permanent magnets cannot be changed.
Materials – Permanent magnets are made from hard materials like steel, while electromagnets
are made from soft materials like copper.
Electricity Supply – To maintain its magnetic field, an electromagnet needs a continuous
supply of electricity. However, permanent magnets do not need electricity to generate their
magnetic field.
Electro-permanent Magnets
Electro-permanent magnets or EPM are permanent magnets whose magnetic field can be
switched on or off by an electrical pulse through a wire winding around a part of the magnet.
Similar to thermocouple devices, EPMs contain two different types of metal, one with a high
demagnetization resistance, and one with a low demagnetization resistance. An electric pulse
can cause the direction of their magnetization to align therefore producing a magnetic field.
Meanwhile, an electric pulse of the opposite polarity can cause their magnetization to oppose,
making them lose their magnetic field.
