History of Permanent Magnets
The history of permanent magnets goes back to ancient times. Records from early Greek, Roman and Chinese civilisations make reference to rare and mysterious stones called lodestones. These lodestones could attract each other and also small pieces of iron. When suspended from a thread it was noted that they always pointed in the same direction. We now know that lodestones contain magnetite, an oxide of iron and that they are a naturally occurring magnet Although lodestones were considered an intriguing phenomenon by scientists of the day, they were not really utilised in any constructive way until around 1200 AD with the introduction of the mariner’s (magnetic) compass. The mariner’s compass is a device housing a pivoting magnetised needle, which freely and consistently points towards magnetic north. This enables travellers to consistently and safely navigate their way from one place to another. Modern research into magnetism is heading in many different directions involving a vast array of materials, however, at this time there are only four types of magnets that are commonly used throughout the world. They are Alnico, Ferrite, Samarium Cobalt and the most recently invented, Neodymium or “Rare Earth magnets”.
Alnico magnets came onto the scene in the 1940’s and they started a revolution in the use of permanent magnets. For the first time, it was now possible to replace electromagnets with permanent (Alnico) magnets. This provided a design flexibility that had previously been unthinkable. The Discovery of these magnets allowed Alnico magnets to replace electromagnets in devices such as generators, electric motors and microphones which was a major technological advancement Alnico magnets are made from Aluminium, Nickel and Cobalt. They have an excellent temperature tolerance of up to 550ﾰC and are relatively corrosion resistant. Alnico’s biggest downfall is its poor resistance to demagnetisation. This instability sometimes makes Alnico unsuitable for certain demanding engineering requirements. Although they are still widely used today, Alnico Magnets are gradually becoming priced out of the market with the availability of newer, high tech and lower priced magnets that are now commonplace.
In the early to mid-1950’s came the creation of Ferrite magnets. Often referred to as ceramic magnets, Ferrites quickly became the preferred choice over Alnico due to their low cost and their strong resistance to demagnetisation. The availability of Ferrite magnets rapidly increased the momentum in the abundance of inventions and improvements to existing products using magnets. Ferrite magnets are used in all manner of products including electronic sensing devices, electric motors, lifting devices and magnetic separators Ferrite magnets are low cost and they have excellent corrosion resistance. They are very hard and as such, they are very brittle. This also makes them difficult to machine or drill holes. They have a very good temperature tolerance with relative magnetic stability at temperatures of up to 250°C.
Samarium Colbalt Magnets
1970 saw the entrance of Samarium Cobalt magnets into the marketplace. In a similar way that Ferrite and Alnico magnets had done before, Samarium Cobalt magnets brought a whole range of new characteristics, applications and possibilities to the industry. Samarium Cobalt magnets have several features that made them far superior to any magnet available during the time. They have a magnetic strength that is several times greater than either Alnico or Ferrite magnets, while at the same time they offer a very high-temperature stability. Temperatures of 300ﾰ C can be easily withstood by Samarium Cobalt magnets and in addition to this, they also demonstrate excellent corrosion resistance. However, samarium cobalt does have its disadvantages two of which are that they are very brittle and therefore extremely fragile and they are a very expensive magnet to produce. Samarium Cobalt magnets properties make them a perfect choice for high strength and high-temperature applications such as stepper motors and furnace sensors etc. Their corrosion resistance opens up numerous opportunities in marine environments and also in chemical industries.
Neodymium (Rare Earth) Magnets
1983 saw the discovery of Neodymium Iron Boron Magnets. The invention of this new magnet was announced almost simultaneously by two separate companies, (General Motors and Sumitomo Special Metals) who were working independently of each other on very different production methods of a very similar product. This announcement created a huge amount of interest as magnet technology had now taken another leap forward to produce an entirely new magnetic material. Neodymium Iron Boron Magnets, or “Rare Earth” magnets as they are more commonly known, are the strongest type of magnet available on today’s market. Their manufacturing process is also considerably cheaper making Neodymium’s a very cost effective. Unfortunately, Rare Earth magnets do have two disadvantages. They have poor corrosion resistance and they are more temperature sensitive than other magnets. However new high-temperature tolerant grades of Rare Earth magnets are being created and released on a regular basis. Rare Earth magnets offer high magnetic energy and good stability making them the logical choice for many electronics and engineering projects. Rare Earth magnets are used in all manner of ways in almost every sector of the magnetics industry such as mining, health, construction, electronics, education and the food industry. They have become the industry standard when size, strength and efficiency are required.
Frequently Asked Questions
How can I identify the poles of the magnets?
There are several simple methods that can be used to identify the (Scientific) North and South poles of neodymium magnets.
- The easiest way is to use another magnet that is already marked. The North Pole of the marked magnet will be attracted to the South Pole of the unmarked magnet.
- If you take an even number of magnets and pinch a string in the middle of the stack and dangle the magnets so they can freely rotate on the string, the North Pole of the magnets will eventually settle pointing north. This actually contradicts the “opposites attract” rule of magnetism, but the naming convention of the poles is a carryover from the old days when the poles were called the “North-seeking” and “South-seeking” poles. These were shortened over time to the “North” and the “South” poles that we know them as.
- If you have a compass handy, the end of the needle that normally points north will be attracted to the South Pole of the neodymium magnet.
- Use one of our Pole Identifier Devices.
Is one pole stronger than the other?
No both poles are equal in strength.
Which is the strongest type of magnet?
Neodymium (more precisely Neodymium-Iron-Boron) magnets are the strongest permanent magnets in the world.
What materials do magnets attract?
Ferromagnetic materials are strongly attracted by a magnetic force. The elements iron (Fe) nickel (Ni) and cobalt (Co) are the most commonly available elements. Steel is ferromagnetic because it is an alloy of iron and other metals.
What materials can I use to block/shield magnetic fields?
Magnetic fields cannot be blocked, only redirected. The only materials that will redirect magnetic fields are materials that are ferromagnetic (attracted to magnets) such as iron, steel (which contains iron), cobalt, and nickel.
Can you supply monopole magnets?
No we don’t, nor does anyone else, because they don’t exist. All magnets must have at least two poles.
Does stacking magnets together make them stronger?
Yes, two or more magnets stacked together will behave exactly like a single magnet of the combined size for example, if you stacked two of our ND155 disc magnets to form a 15 x 10mm combined size magnet, the two magnets would have the same strength and behave identically to our ND1510 discs, which are 15mm diameter x 10mm thick.
How to measure the strength of a magnet?
Gaussmeters are used to measure the magnetic field density at the surface of the magnet. This is referred to as the surface field and is measured in Gauss (or Tesla). Pull forces are used to test the Holding force of a magnetic that is in contact with a flat steel plate. Pull forces are measured in pounds (or kilograms).
Will a magnet with a 20 kg pull force lift a 20 kg object?
Because pull force values are tested under laboratory conditions, you probably won’t achieve the same holding force under real-world conditions. The effective pull force is reduced by uneven contact with the metal surface, pulling in a direction that is not perpendicular to the steel, attaching to metal that is thinner than ideal, surface coatings, and other factors.
What are neodymium magnets? Are they the same as “rare earth”?
Neodymium magnets are a member of the rare earth magnet family. They are called “rare earth” because neodymium is a member of the “rare earth” elements on the periodic table. Neodymium magnets are the strongest of the rare earth magnets and are the strongest permanent magnets in the world.
What are neodymium magnets made from and how are they made?
Neodymium magnets are actually composed of neodymium, iron and boron (they are also referred to as NIB or Knife magnets). The powdered mixture is pressed under great pressure into moulds. The material is then sintered (heated under a vacuum), cooled, and then ground or sliced into the desired shape. Coatings are then applied if required. Finally, the blank magnets are magnetized by exposing them to a very powerful magnetic field.
What does the “N rating”, or grade of the neodymium magnets mean?
The grade, or “N rating” of the magnet refers to the Maximum Energy Product of the material that the magnet is made from. It refers to the maximum strength that the material can be magnetized to. The grade of neodymium magnets is generally measured in units millions of Gauss Oersted (Moe). A magnet of grade N42 has a Maximum Energy Produce of 42 MGOe. Generally speaking, the higher the grade, the stronger the magnet.
Can I cut, drill, or machine neodymium magnets?
The Neodymium Iron Boron material is very hard and brittle, so machining is difficult at best. The hardness of the material is RC46 on the Rockwell “C” scale, which is harder than commercially available drills and tooling, so these tools will heat up and become damaged if used on Knife material. Diamond tooling, EDM (Electrostatic Discharge Machines), and abrasives are the preferred methods from shaping neodymium magnet material. Machining of neodymium magnets should only be done by experienced machining familiar with the risk and safety issues involved. The heat generated during machining can demagnetise the magnet and could cause it to catch fire posing a safety risk. The dry powder produced while machining is also very flammable and great care must be taken to avoid combustion of this material.
Can I solder or weld to neodymium magnets?
You definitely cannot solder or weld to neodymium magnets. The heat will demagnetize the magnet and could cause it to catch fire posing a safety risk.
Do I have to worry about temperature with neodymium magnets?
Yes, Neodymium Iron Boron magnets are sensitive to heat. If a magnet heated above its maximum operating temperature [176ﾰ Farenheight (80ﾰ C) for standard N grades] the magnet will permanently lose a fraction of its magnetic strength. If they are heated above their Curie temperature (590ﾰ F (310ﾰC) for standard N grades), they will lose all of their magnetic properties. Different grades of neodymium different maximum operating and Curie temperatures.
What is the Gauss rating of your magnets?
This depends on the context it is used. Most magnetic therapy people like to present the largest number possible, so they often use the Residual Flux Density (Brmax) of the material, which really doesn’t specify much about the actual magnet. This value is essentially the magnetic field density inside the magnet material. Since you will never be inside the magnet or use the field inside the magnet, this value doesn’t really have any practical value. The surface field of a magnet is a much more accurate specification for a magnet. The surface field is exactly what it sounds like. It is the magnetic field density at the surface of the magnet as measured by a Gaussmeter and this is how we rate all our magnets.
Do neodymium magnets require a keeper?
No, neodymium magnets do not require a keeper for storage like Alnico magnets.
Will my neodymium magnets lose strength over time?
Very little. Neodymium magnets are the strongest and most permanent magnets known to man. If they are not overheated or physically damaged, neodymium magnets will lose less than 1% of their strength over 10 years – not enough for you to notice unless you have very sensitive measuring equipment. They won’t even lose their strength if they are held in repelling or attracting positions with other magnets over long periods of time.
Will neodymium magnets lose strength if they are held in repelling or attracting positions for a long time?
In most applications, the answer is simply “no”. If the magnets will be exposed to higher temperatures while in repelling applications, the answer is ‘possibly’. The exact answer is a bit too complicated for a FAQ answer, and require specifics about the application.
Can I make a magnet that I have any stronger?
No, once a magnet is fully magnetized (saturated), it cannot be made any stronger.
I have metal dust all over my magnets. How can I remove it?
Using adhesive tape to capture the metal dust is the best way to clean magnets.
Why are most neodymium magnets plated or coated?
Neodymium magnets are composed mainly of Neodymium, Iron, and Boron. If neodymium magnets are not plated, the iron in the material will oxidize very easily if exposed to moisture. Even normal humidity will rust the iron over time. To protect the iron from exposure to moisture, most neodymium magnets are plated or coated.
Can I paint over the nickel plating?
Yes, you can use any paint formulated for use on metal surfaces. Spray-on paint seems to work best.
What is the best adhesive to use with your magnets?
We and several customers have had great success adhering to the nickel-plating using Loctite 39205 with Loctite 7380 activator. A Loctite representative also has also recommended Loctite 3032 with Loctite primer 770. For more commonly found adhesives, we have also had good results using Plesxus Methacrylate adhesive, “Liquid Nails”, and “Gorilla Glue”, which are available in most hardware and home supply stores.
I need a special size/shape of neodymium magnet. Can you supply custom magnets?
Yes, we can supply custom magnets. Advise us of the size and quantity you require and we will give you a quote?
Are there health or safety concerns with neo magnets?
There are no known health concerns with exposure to permanent magnetic fields. In fact, many people believe that magnets can be used to speed up the healing process. There may be issues with people with pacemakers handling or being around strong magnets we are not medical professionals, so we cannot offer guidance on pacemaker safety. Please consult a physician for this information. There are several safety concerns when handling strong magnets.
What is a safe distance to keep magnets away from pacemakers?
We are not medical professionals, so we cannot offer guidance on pacemaker safety. Please consult a physician for this information.
Will magnets harm my electronics?
Maybe… the strong magnetic fields of these magnets can damage certain magnetic media such as optical media, credit cards, magnetic I.D. cards or other such devices. They can also damage televisions, DVD players, computer monitors and other displays. Never place neodymium magnets near any of these appliances. As for other electronics such as cell phones, iPods, flash drives, calculators and similar devices that do not contain magnetic storage media, probably not, but it is best to err on the safe side and try to avoid close contact between neo magnets and electronics.
Will using magnets on my refrigerator, stove, oven, or microwave harm the appliance?
Magnets will not harm any of these appliances.
Will magnets erase my hard drive or harm my computer?
Not unless you really work at it. While you probably don’t want to stick magnets directly to your computer case, having them nearby will not harm your computer. Magnets can damage Optical storage media and magnetic media such as magnetic tape, so you must keep magnets away from these items. They will not, however, damage any data on your hard drive unless you place a very large and powerful magnet directly on top of the drive. Every hard drive already contains a powerful neodymium magnet, so one moving around outside the case will not affect the data. Storage such as Solid state drives are immune to magnetic fields as data is written electronically not magnetically like a hard disk drive (HDD).
Which magnets should I use for holding pins/badges through clothing instead of using pins?
For holding average-sized pins and badges, we recommend our BadgeMag as they provide the appropriate amount of pull strength through a wide range of fabric thicknesses.
I need magnets for a binder/brochure closure. Which magnets work for this?
We have many printers and other customers that use our magnets in brochures and binders to hold them closed. The most common sizes used for brochures and binders are our ND916, ND925, ND121ADH sold by the pair, ND201ADH sold by the pair.