What Is a Permanent Magnet? Complete List Of Perma-Magnets
Permanent magnets are most commonly seen in the household within the magnets used to hold papers and notes on refrigerator doors. They also are used in things like purse clasps, MRI machines, and cell phones. There are a lot of individual details to learn about permanent magnets, which is why I did all of the research on the topic.
What is a permanent magnet? Permanent magnets are magnets that continue to persistently create a magnetic field. This permanent field is continuously created by the structure of the magnet, which has an inherent positive and negative end.
There are two types of magnets that are commonly referred to. There are temporary magnets, and there are permanent magnets. Surprisingly, you are almost guaranteed to have both kinds of magnets commonly within your home.
However, in this article we will be focusing in on permanent magnets: from what they are to their different types as well as how you can characterize them. Keep reading to find out everything you need to know about these intriguing objects.
What Is a Permanent Magnet?
All permanent magnets have their own persistent magnetic field. This magnetic field is also sometimes referred to as the magnetic flux density, or the magnetic B field, which sounds more like something you would see in a sci-fi film.
Permanent magnetic materials can magically attract some specific materials from a distance since they generate this magnetic field. These fields extend out invisibly beyond the magnet itself.
This magnetic field that permanent magnets create around themselves is what causes them to stick to certain kinds of metal.
The kinds of metal that these magnets can stick too usually is iron, or any kind of metal that contains iron like steel. They also stick to cobalt, nickel, gadolinium, lodestone, and manganese. These metals are commonly referred to as ferromagnetic materials.
Examples of Ferromagnetic Materials:
|Cobalt||Co||High melting point (resistant)|
|Steel||Combination/Alloy||Mixture of nickel, boron, titanium, manganese, etc.|
|Manganese||Mn||Brittle with high melting point|
|Nickel||Ni||Malleable and Ductile element|
|Gadolinium||Gd||Rare-earth metal (somewhat malleable and ductile)|
|Terbium||Tb||Soft metal, ductile, malleable|
|Dysprosium||Dy||Soft metal, sensitive to damages|
Ferromagnetic materials are characterized not only by their inherent material makeup, but also by the crystalline structure. Most of these materials are metals, which means it is pretty difficult to make a ferromagnetic insulator.
The real question is how these magnetic fields are created. Magnetic fields, simplified, are basically what electrical fields change into when an object that has been electrically charged begins to move. This may sound confusing, since magnets that you think of seems like just pieces of metal.
Within magnets, which at a surface level just seem like a metal material, there are tons of electrons that spin around atoms. This leads us to a concept called the magnetic moment.
All magnetic fields have a magnetic moment. Though there is a lot of complex science that can go into explaining what the magnetic moment is, it is much more easily summarized by saying that it is a vector that defines the magnet’s general magnetic properties.
In even more simple terms, small particles that have an electric charge are tiny little magnets.
An easy example is to think of a rectangular magnet. This magnet will have a north pole and south pole. The magnetic moment will point from the south pole of this magnet, to the north pole!
Magnets will always either repel or attract one another. This has to do with the positive and negative poles of a magnet, also known as the north pole and south pole. The best way to remember how these interact is to remember that opposites attract.
The north pole of a magnet will be attracted to the south pole of another magnet. Likewise, the north pole of a magnet is going to be repelled by the north pole of another magnet.
To summarize, permanent magnets have a persistent magnetic field, which is what sets them apart from temporary magnets.
This magnetic field has a north pole and south pole. They interact with ferromagnetic materials most commonly, but also have an effect on paramagnetic materials and diamagnetic materials.
All magnets have something called a magnetic moment, which is a complex concept that helps explain magnetic fields.
The Different Types of Permanent Magnets (Complete List)
There are many types of permanent magnets, which you can find in the list down below.
Types of Permanent Magnets:
- Neodymium (which is an alloy of neodymium, iron, and boron)
- Samarium cobalt
- Injection molded
One of the most commercially powerful permanent magnets is the neodymium magnet. This kind of magnet is called a rare earth magnet, as neodymium is classified as a rare earth element.
Neodymium magnets are made up of an alloy of neodymium, iron, and boron. The iron within the magnets is to help raise the temperature at which they will hold their magnetic charge. The boron helps with bonding.
While neodymium magnets are some of the strongest magnets out there, they also oxidize very easily and require a protective coating often made from nickel, or a copper nickel combination. They also are quite brittle, but this isn’t unique to neodymium magnets.
These magnets can be costly, but relative to their strength they are quite cheap. They require extremely small amounts due to their power. They are often used when the small size is particularly advantageous, like in very small jewelry clasps or in the clasps on accessories like purses and bags.
There are different grades of neodymium magnets. The higher the number within the grade, the higher the strength of the magnet.
For example, N52 is more powerful than N42. With that being said, the price gets exponentially higher as the grade goes up, and the magnets can get more brittle. Because of this, though the most powerful grade is N55, N42 is the most commonly used.
Samarium cobalt permanent magnets are also a rare earth magnet. In comparison to neodymium, they are quite a bit weaker, however they make up for that in durability.
These magnets can stand extremely high operating temperatures, making them a great choice for niche applications that need the magnet to withstand heat.
Unlike neodymium magnets, samarium cobalt magnets also don’t need to be coated and are inherently resistant to corrosion.
With that being said, they also are quite brittle, and is extremely costly. Because of the high cost, they are almost always only used when the high resistance to corrosion and high operating temperature is necessary.
Alnico magnets, though much weaker than rare earth magnets, have uses as well. As their name implies, they are made up mainly of aluminum, nickel, and cobalt.
As with most of the magnet types we will be mentioning, they have trace amounts of other elements in order to help enhance things like operating temperature and resistance to corrosion.
The alnico strain of permanent magnets work well in higher heats, however they are quite easily demagnetized by other magnetic fields. They can be made in multiple ways, however they usually are made via sintering or casting.
Alnico magnets were much more popular in the past, however with the increased production of ceramic permanent magnets as well as rare earth magnets, they have become less popular.
They are a high cost magnet that very often doesn’t have as much power as it’s counterparts. These magnets used to be used more commonly in audio speakers, but have been slowly replaced by neodymium magnets.
The grades of alnico magnets are anisotropic, the most common being eight, five, and two. The lower grades can be magnetized in whatever direction is preferred, but this also causes the magnetic strength to be weaker.
Ceramic magnets are a very common type of magnet. These magnets are also known as ferrite magnets. They are commonly created from iron oxide, and either strontium carbonate or barium.
Because of the materials used to create these magnets, they are quite cheap to produce in very large quantities. This also means the magnets are one of the cheaper magnets on the market.
When making ceramic magnets, a few processes can be used. Often they are either sintered or pressed. Because of how brittle these magnets are, very special tools are needed if they need to be ground.
They are also anisotropic, which means that their magnetic field is created in the same direction as the pressing takes place.
Ceramic magnets are commonly used in households for things like fridge magnets, sensors, and door catches. Their price also makes them a great choice for personal projects and small carpentry.
There are grades of ceramic, which are very similar to alnico grading in that it is anisotropic. Ceramic-1, while potentially weaker, has magnetic properties in any direction. There are also grades ceramic-5 and ceramic-8 that are commonly used.
Injection molded magnets are a combination of magnetic element powders that are blended together with a variety of polymer materials as a base.
There is an extremely wide range of products available, and many of these combinations include the magnetic materials used in the previously mentioned magnets.
The benefits to injection molded magnets is that they can be made into much more complex shapes. This makes them ideal for very specific builds or projects, and are often custom-engineered to fit a specific dimension.
Due to the process of injection molding, this usually is a very high cost magnet variety in comparison to things like your typical ceramic magnet.
They also often have a low max operating temperature, but can make up in that they often have a very high corrosion resistance.
Since injection molded magnets can be made out of a variety of materials, they have differing strengths. Because of the mixture used in this process, however, they often end up being weaker than their pure counterparts.
Another type of permanent magnet that is similar to the injection molded variety are flexible magnets.
These magnets are produced in flat sheets, which can allow for bending. These are usually made by combining a magnetic material with some kind of plastic binding agent. In order to press this mixture, a special extruder machine is used.
These magnets are used for specific applications that require bendable shapes that won’t crack or become easily damaged. Like injection molded magnets, they are not as strong as their permanent magnet counterparts due to the plastic binding agent.
Due to the low price of production, and the lower price of the plastic binding agent, these often are a very low cost choice. Though they have low power and also a low max operating temperature, they have a high resistance to corrosion.
Flexible magnets are used in a ton of applications. A common use is for advertising or promotional items that can be stuck right on the fridge. They are also used in car components and watches. It is also a great option for home crafts.
Characteristics Of a Permanent Magnet
As we have covered, permanent magnets are called so because they continuously create a magnetic field. While this field does deteriorate over time, it can take years and years, sometimes even centuries, before the magnets become ineffective.
These invisible fields that permanent magnets persistently create can attract other magnets at a distance, whether temporary or permanent.
To look at the specific characteristics of permanent magnets, one of the first things we should talk about is how we measure the strength of their magnetic field. Depending on the type of magnet, there are dramatically different strengths.
In order to compare different types of magnets, we should first talk about the measurements used.
MGOe, or mega gauss-oersteds, is used to measure the energy stored within a magnet. This is also called the maximum energy product, or the magnet performance. While we can compare typical MGOe, it is important to note that this depends dramatically on the manufacturer and the materials used to make the magnet.
Approximate Strength of Permanent Magnets (In MGOe):
- Neodymium magnets – 40-55 MGOe
- Samarium cobalt magnets – 15-30 MGOe
- Alnico magnets – 5.5 MGOe
- Ceramic magnets – 3.5 MGOe
- Injection molded and flexible magnets vary dramatically depending on the materials used.
Let’s put some of these numbers into a more understandable format. If a 1” x 1” x ½” thick piece of neodymium magnet had a MGOe of 52, it would take about 65 pounds of force to pull it straight off of a piece of steel.
To put that into perspective, a person can safely pull 30% of their body weight. That means that a 150 pound person could only safely pull up to 45 pounds of force. That wouldn’t be nearly enough to remove this magnet from steel!
As you can see, ceramic magnets and alnico magnets are significantly less powerful than the two types of rare earth magnets.
Again, it is important to note that while injection molded magnets and flexible magnets vary, they are dramatically less strong than their normal magnet counterparts.
Another commonly measured characteristic of permanent magnets is the max operating temperature.
This is the max heat that a magnet can be in without becoming demagnetized. There also is a curie temperature, which is the temperature at which the magnet completely loses its magnetic field.
When magnets are exposed to heats above their max operating temperature, two things can happen. If the temperature is only slightly above the max operating temperature, then the magnet is only less effective when it is overheated.
Once it cools down, it will regain its original power. If the magnet is exposed to temperatures that are significantly above the max operating temperature, they permanently loose magnetic power even after completely cooling.
Even with this being said, you can repair magnets that have become demagnetized if it goes through a strong enough external magnetic field.
This number also varies quite a bit between the different types of permanent magnets. Neodymium magnets have an approximate max working temperature of about 176 degrees Fahrenheit, while their curie temperature is closer to 590 degrees Fahrenheit.
In comparison, samarium cobalt magnets which are known for their high operating temperatures have a max working temperature of about 1,020 degrees Fahrenheit, with a curie temperature of 1,470 degrees Fahrenheit.
Alnico magnets, while less powerful, actually have a pretty temperature tolerance as well. Their max operating temperature is usually about 1,000 degrees Fahrenheit, and their curie temperature is about 1,400 degrees Fahrenheit.
Ceramic magnets, the other weaker variety of magnet, only has a max operating temperature of 480 degrees Fahrenheit and curie temperature of 840 degrees Fahrenheit.
So, while both the samarium cobalt magnets and alnico magnets are expensive, they have extremely high temperature tolerance. The largest difference between the two is their dramatically different magnetic field strength.
On the other hand, both neodymium and ceramic magnets are less heat tolerant, but neodymium is quite a bit less so. Ceramic magnets are cheaper than neodymium, however exponentially less powerful.
These differences are what makes all of these magnet types special depending on the application.
If you are looking for a cheap magnet with a substantial max operating temperature, ceramic magnets are potentially the right choice for your project. If you need an extremely powerful magnet however it will be a hot environment, perhaps samarium cobalt magnets would be best.