Dr Ewan Goodier is Technical Manager at Eclipse Magnetics. He has worked extensively in magnetic system design and has a PhD in Electrical Machine Design and Permanent Magnets. Here, he answers some common magnetic questions (click on the question to see the answer).
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Frequently Asked Questions
What Are Magnets & What Is Magnetism?
A magnet is an object that can create an invisible magnetic field which can be used to interact with other magnetic fields (attraction or repulsion) or to attract to ferromagnetic materials such as iron, mild steel, cobalt and nickel. Magnetic fields always exit the magnet from its North pole and enter the magnet at its South pole.
There are three types of magnet. Permanent Magnets (Hard Magnets) produce a magnetic field all the time. Electromagnets produce magnetic fields only when electrical current passes through an electrical conductor (ideally in the shape of a coil). Soft magnets are temporary – they only produce magnetic fields while an external magnetic field is present and lose nearly all their magnetism once the external field is removed.
Magnetism is the physical event due to the forces occurring between magnets – it is noticed as attraction or repulsion. All materials will experience magnetism (except a vacuum). Some are strongly attracted to magnetic fields (ferromagnetic materials). Some are weakly attracted (paramagnetic materials). Some are actually very weakly repelled (diamagnetic materials). Some are attracted reasonably strongly (antiferromagnetic materials).
Magnetism can only be seen with the aid of other materials (e.g. iron filings, ferrofluid, compasses) – the materials align with the lines of magnetic flux (the field lines) to indicate how the magnetism moves around the magnet (they can impact on the actual field paths). Magnetic field lines are 3 dimensional – they can travel in all directions and interact with all materials (they can even pass through vacuums).
How Long Do Magnets Last?
As permanent magnets, neodymium magnets perform at their peak every 100 years if maintained at optimum conditions. A magnet's lifespan can be shortened by two factors:
- Heat - Magnets lose magnetism if their temperature exceeds the maximum operating temperature (80°C for N42-grade neodymium magnets). Samarium cobalt magnets are not as strong as neodymium magnets, but they operate at temperatures as high as 350 degrees Celsius.
- Corrosion - The magnet will rust if the plating on it is damaged and water gets inside, resulting in deteriorated performance. Magnets made with samarium cobalt and ferrite resist corrosion but are not as strong as neodymium magnets
What Is the Strongest Part of a Magnet? or Where is a Magnet the strongest ?
Basically, the pole of a magnet is its strongest part. It doesn't matter how small the magnet is; it will always have two poles. The magnet will always point to the south when it is stationary on a horizontal plane, and the pole will always point to the north when it is stationary on a horizontal plane. The pole pointing south is called the South Pole (S pole), and the pole pointing north is called the North Pole (N pole).
Where is the Strongest Magnetic Field around a Bar Magnet ?
Magnetic fields are strongest at either pole of a bar magnet. There is no difference between the north pole and the south pole in its strength.
Does Stacking Magnets Make Them Stronger?
Stacking multiple magnets together can make them stronger. The combined strength of two magnets the same size or smaller will be virtually equal to the strength of a single magnet. However, It is impossible for a magnet to become stronger if it has been fully magnetised. By stacking magnets together, the strength of the stack increases until its diameter equals its length. Any further magnets added after this point will give only a marginal performance boost.
What's N52 Neodymium Magnet?
A neodymium magnet grade of N52 has a BHMax of 52MGOe (MGOe stands for Mega-Gauss Ohresteds) energy product. There are currently no permanent magnets stronger than a N52 rare earth magnet, and it is the most powerful magnet in the world. The neodymium magnets with a "N" followed by any of "35", "40", "42", "45", "48", "50" or "52" indicate the magnet rating. The number represents the maximum weight that can be magnetised. Along with being an indication of the magnet's strength, the number is also a measure of the strength in Megagauss Oersted. According to the N rating system, a 52 is the strongest.
Do Neodymium Magnets rust?
Like iron, neodymium magnets tend to rust if left unprotected. Nickel-copper-nickel (Ni-Cu-Ni) is a three layer plating most neodymium magnets use to prevent corrosion. For many years, corrosion protection has been provided by this specific plating combination.
Why is Neodymium so Magnetic?
The ferromagnetic nature of neodymium makes it magnetic. Having the capability of being magnetized or attracted by a magnet. As a rare-earth material, neodymium can be made into a powerful magnet by combining it with iron and boron.
What Temperature do Neodymium Magnets lose their Magnetism?
Magnetism is caused by alignment of the atoms in a magnet between its two poles, under normal conditions. Heat, however, causes these atoms to begin to move faster and more sporadically. As a result of the jumbling, magnetism is lost. Therefore, Neodymium magnets are sensitive to extreme heat. As soon as the temperature rises above 80°C, the magnet's pull starts to decrease. Magnets that are quickly returned to room temperature will be able to regain their full magnetism. The magnetism of a material can be permanently destroyed if left at temperatures above 80 °C for an extended period of time.