Magnets attract and repel with invisible forces.
But what determines the strength of a magnet?
In this post, we’ll dive into the key factors that influence magnetic strength.
You’ll learn important things like material composition, magnet grades, sizes and shapes, and more.
And, also learn how temperature, magnetization, and surface contact affect a magnet’s pull force.
By the end, you’ll have a solid understanding of what makes some magnets much stronger than others.
Let’s dive in!
What is Magnet Strength?
Magnet strength refers to the ability of a magnet to attract or repel other magnets or magnetic materials.
Several key factors determine the strength of a magnet:
Material composition
Different magnetic materials have varying inherent strengths.
Rare earth magnets like neodymium (NdFeB) and samarium cobalt (SmCo) are the strongest.
Followed by alnico, and then ceramic or ferrite magnets.
Magnet grade
Within each material type, magnets are graded by their maximum energy product (BHmax), measured in Mega Gauss Oersteds (MGOe).
Higher grade numbers like N52 indicate a stronger magnet than lower grades like N35 for neodymium magnets.
Size and shape
Larger magnets are generally stronger than smaller ones of the same material and grade.
The shape also impacts the concentration of magnetic field.
Temperature
Magnets lose strength when exposed to temperatures above their maximum operating range, which varies by material.
Neodymium has the lowest and alnico the highest temperature tolerance.
Magnetization
How completely and uniformly a magnet is magnetized to saturation affects its strength.
Air gaps and surface contact
Any gaps between a magnet and the attracted material, due to rough surfaces or coatings, will reduce the effective pull force.
Magnet strength is quantified in several ways:
- Pull force in pounds or kilograms to separate a magnet from a thick steel plate
- Flux density in Gauss or Teslas of the magnetic field at a given distance
- Maximum energy product (BHmax) as an overall figure of merit
In summary, magnet strength depends on a few things:
- Material properties, magnet grade, physical dimensions, operating conditions, and measurement method.
- Choosing the optimal magnet requires carefully considering the specific application requirements.
Measuring Magnet Strength
There are several ways to measure the strength of a magnet:
Magnetic field strength (H)
This measures the strength and direction of the magnetic field at a particular point near the magnet.
- It is typically measured in amperes per meter (A/m) or oersteds (Oe).
- A magnetometer or gaussmeter can be used to measure magnetic field strength.
Magnetic flux density (B)
Also known as magnetic induction.
This measures the actual magnetic field within a material, expressed as a concentration of magnetic flux per unit cross-sectional area.
- It is measured in teslas (T) or gauss (G). 1 tesla = 10,000 gauss.
Maximum energy product (BHmax)
This is the maximum product of the magnetic flux density B and magnetic field strength H.
It indicates the overall strength or “magnetic potential” of a magnet
- Measured in megagauss-oersteds (MGOe).
- The higher the BHmax, the stronger the magnet.
Pull force
This measures the maximum weight or force required to separate a magnet from a steel plate.
It provides a practical indication of a magnet’s strength in terms of how much it can lift or attract.
- Pull force is typically measured in pounds or kilograms.
Gauss meter or flux meter
These instruments can directly measure the magnetic flux density at various points on a magnet’s surface or at a distance.
- This provides a detailed map of the magnet’s field strength.
In summary, a magnet’s strength can be quantified by its magnetic field intensity, flux density, maximum energy product, and pull force.
Magnetometers, gauss meters, and pull force tests are common methods to experimentally measure these properties.
The choice of measurement depends on the specific application and the aspect of magnetic strength that is most relevant.
Strongest Magnet Strength
The magnets with the strongest magnetic strength are rare earth magnets, specifically neodymium (NdFeB) magnets.
Here are the key points:
Rare earth magnets, which include neodymium and samarium cobalt:
- They are the strongest type of permanent magnets available.
- Produce significantly stronger magnetic fields than other types such as ferrite or alnico magnets.
Neodymium magnets are considered the most powerful commercially available magnets.
- They can have a maximum energy product (BHmax) up to 40 MGOe, which is a measure of a magnet’s overall strength.
In comparison,
- Samarium cobalt magnets have a BHmax ranging from 16 MGOe to 32 MGOe
- Alnico magnets range from 5.5 MGOe to 10 MGOe.
- Ferrite (ceramic) magnets have a BHmax around 3.5 MGOe.
The magnetic field strength,
- Neodymium magnets can exceed 1.2 teslas
- Ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla.
- Neodymium magnets have a very high coercivity, meaning they are extremely resistant to demagnetization.
So in summary, while there are various types of permanent magnets available, rare earth neodymium (NdFeB) magnets exhibit the highest magnetic field strength and energy product, making them the strongest type of permanent magnet currently available.
Samarium cobalt magnets are the second strongest rare earth magnet type.
Common Misunderstandings
Here are some common myths and misunderstandings about magnet strength:
1. All metals are attracted to magnets.
- While magnetic materials are always metals, not all metals are magnetic.
- Iron, nickel, cobalt and some rare earth elements are attracted to magnets.
- Most other metals like copper, gold, aluminum and zinc are not magnetic.
2. The size of a magnet dictates its strength.
- A larger magnet is not always stronger than a smaller one.
- The material composition is more important in determining magnetic strength.
- For example, a small neodymium magnet can be much stronger than a large ceramic magnet.
3. Magnets will erase computer hard drives.
- Theoretically possible with an extremely powerful magnet.
- However, the magnets found in common household items are not nearly strong enough to affect a hard drive.
- Most hard drives have strong built-in magnets already.
4. Magnets lose strength over time.
- Permanent magnets can lose some strength very gradually over long periods of time, but this is usually negligible.
- Factors like heat, physical damage, reluctance changes and external magnetic fields are more likely to weaken magnets than simply the passage of time.
5. Magnetic fields exist only outside a magnet.
- The magnetic field lines actually pass through the inside of the magnet as well.
- They go from the south pole to the north pole to form a complete loop.
6. Magnets increase blood flow.
- While often repeated, research studies have not conclusively shown that static magnetic fields significantly increase blood flow.
- Especially, in healthy individuals.
- The therapeutic effects of magnets likely stem from other mechanisms.
7. Magnets emit harmful radiation.
- The magnetic fields produced by permanent magnets do not constitute the type of electromagnetic radiation that can be harmful to human health.
- Magnetic fields are distinct from radiation like x-rays or gamma rays.