Overview of Neodymium Magnet Measurement Methods
The first and most common question people ask about neodymium magnets is their strength. If you’re holding a piece of This can be done through various methods, such as filtration, magnetic nano adsorbents, magnetic water treatment, AOPs, etc., neodymium magnet, and you bump into someone, they will most likely ask you, “how strong is it?” This curiosity, of course, is normal because a neodymium magnet’s strength is its value.
When people shop for neodymium magnets online, the first thing they often look for among the specifications is “strength.” In this case, they usually look for how much weight they should expect the neodymium magnet to pull or hold or how strong they can expect the magnetic field to be.
The problem, however, is that when we talk about a neodymium magnet’s strength, several other factors come into play. All of which affect the neodymium magnet’s strength in one way or another. And for all of these factors, which also bear different names, there are different measurement methods. In this article, we will consider different neodymium magnet testing equipment and measurement methods of neodymium magnets.
Magnet Measurement Equipment
The following are some of the most popular equipment professionals use to measure neodymium magnets.
Micrometer
The micrometer, also known as a micrometer screw gauge, is a tool that incorporates a calibrated screw. It is commonly used to take accurate linear measurements of dimensions such as length, width, diameter, and height of solid materials.
Slide Caliper Rule
The slide caliper rule is an instrument with one fixed jaw and one movable jaw. You can use it to measure objects’ inside and outside dimensions. Using the caliper rule involves sliding the movable jaw back and forth the dimension to be measured. Four types of the caliper rule include the Vernier, digital, and dial caliper. The difference is only in the way they display measurements.
Gaussmeter
A gaussmeter is a device that can measure the strength and direction of a relatively small magnetic field. To measure larger magnetic fields, a Tesla meter is used instead. To better understand the difference, you can see Gauss as equivalent to a megabyte and Tesla as equivalent to 10 gigabytes. Both gaussmeter and Tesla meter are classified as magnetometers.
Fluxmeter
A fluxmeter is an electronic digital display instrument used to measure the magnetic flux of a permanent neodymium magnet. It can be used for quality control and sorting magnetic products. Magnetic flux refers to the amount of magnetic field that passes through an area.
Tesla Meter
As explained above, a Tesla meter measures relatively large magnetic fields. It functions exactly like a gaussmeter, but its measurement value is in Tesla, which is 10,000 times larger than Gauss. I.e., 1 tesla equals 10,000 Gauss.
Pull Tester
The pull tester is a device we use to measure the strength of neodymium magnets to help determine how effective they would be in their applications. It is also used to compare two neodymium magnets that look alike but may possess different strengths.
Permanent Neodymium Magnet Characteristics Automatic Tester
This machine helps to perform various analyses of our products like defect analysis, process analysis, and others. It can help detect and analyze the characteristics of metal materials and the possible causes of failure in production and application. The production process can then be improved for better end products.
Magnetic Property Detector
Magnetic Property Detector or magnetic sensors are devices that can detect magnetic fields through non-magnetic materials. They can also be used in security applications such as the detection and localization of ferromagnetic objects.
Image Mapping Instrument
An image Mapping Instrument can quickly detect variations in complex products where precision is essential. They can detect contours and size variations on surfaces, angles, and dimensions. They help with quality control and ensure customers’ requirements are met.
Fully Automatic Optical Size Detector
Automatic optical size detectors are also known as CNC image measuring machines. They are used in industrial processing, where the machine automatically uses image processing software to perform fast and accurate measurements. They help detect products with uneven edges to ensure they don’t make shipping.
Salt Spray Test Chamber
This chamber is used to test the surface coating of neodymium magnets to check the resistance of the coating against a corrosive environment. Then we can project the durability of the coating.
PCT Test Chamber
The Pressure Cooker Test chamber is used to test the resistance of our neodymium magnets against moisture, high pressure, and high temperature. It helps to analyze their performance in application in harsh environments.
Spectroscopic Coating Thickness Gauge
We use a spectroscopic coating thickness gauge to measure the thickness of the coating on our neodymium magnets. It helps to meet the customer’s expectations in case of custom orders and check other information such as the coating components, performance, expected life, and compliance with international standards.
Neodymium Magnet Intrinsic Performance Analysis
The Maximum Energy Product
The maximum energy product, or BHmax, refers to the maximum energy density a neodymium magnet can hold. It is the maximum magnetic flux density and field strength product for a piece of neodymium magnet.
This metric indicates strength. And it is not affected by size or volume, which means that two neodymium magnets of different sizes but the same rating, such as N48 or N42SH, will have the same maximum energy product. However, they generate vastly different magnetic fields.
Although the size of a neodymium magnet does not affect its maximum energy product, it bears some significance. That’s because the size and BHmax of a neodymium magnet required for an application are inversely proportional. I.e., as one goes up, the other goes down.
Why is this so?
Naturally, a larger neodymium magnet can generate larger magnetic fields and more flux than a smaller neodymium magnet because of its volume. Hence, it is stronger.
On the other hand, a smaller neodymium magnet has fewer magnetic fields and less flux. Hence m, it is weaker. If used in the same application, the smaller neodymium magnet will reach BHmax faster than the larger one.
So for your needs, you can purchase either a large neodymium magnet with a lower max energy product or a small neodymium magnet with a higher max energy product. The bottom line is that as your required material volume reduces, your required BHmax should increase.
We measure our neodymium magnets’ max energy product in MGOe, and the number in a product grade indicates this. For instance, the 48 in N48M indicates that the product has a maximum energy product of 48MGOe. The larger this number, the higher the BHmax. The M after 48 in the example above indicates its intrinsic coercivity.
We’ll get into that later.
The Pull/Holding Force
The pull force refers to the force or energy required to pull a neodymium magnet free from a steel plate vertically without sliding or tilting it sideways. Usually, the pull force gives an idea of the neodymium magnet’s holding power, and we can also rely on it to measure the neodymium magnet’s maximum strength. Unlike the maximum energy product, which is measured in MGOe and KJ/m³, the pull force is measured in pounds and kilograms.
It is noteworthy that a neodymium magnet may not be able to exercise its full strength or force during use. Other factors affect the actual pull force of a neodymium magnet during application. These factors include the surface, placement, material permeability, and air gap.
The surface: also called attaching surface, is the load to which the neodymium magnet is attached. When measuring a neodymium magnet’s pull force in a controlled environment, we use a thick, flag, solid steel larger than the tested neodymium magnet. In real-life applications, however, the attaching surface usually differs. Coating and an uneven surface can affect the neodymium magnet’s pull strength.
Placement: when testing a neodymium magnet’s pull strength, we usually fix the neodymium magnet vertically, usually to the underside of a steel beam. In this situation, the neodymium magnet can use its full force. But in a horizontal placement, a neodymium magnet will only hold a maximum of 30% of its total force.
Material permeability: refers to the surface’s ability to absorb magnetism. Neodymium magnets will stick harder to materials with high permeability than those with low permeability. While steel is one of the most permeable materials, gold, silver, chrome, brass, marble, plastic, and tile have zero permeability. Hence, neodymium magnets won’t stick to them.
Air gap: if there is anything between your neodymium magnet and the surface you’re attaching it to, be it coating, paper, paint, wood, foam, and others, that is the air gap, and it can make a big difference in a neodymium magnet’s pull force.
To measure the pull force of a neodymium magnet, you will need a pull force tester. But the equation to calculate it is mass divided by acceleration. I.e., the mass of the load divided by the pull speed.
Remanence
Remanence, sometimes called residual magnetism or retentivity, refers to the magnetic field stored in a ferromagnetic material after removing it from an external magnetic field that is enough to give it saturation.
Magnets, including neodymium magnets, don’t have magnetic abilities right from the beginning of production. They’re first manufactured into the desired shape and then exposed to an external magnetic field to make them magnetic.
After exposure to external magnetic force, hard magnetic materials like neodymium retain a high degree of magnetism permanently, and they don’t lose it quickly. And because neodymium magnets have higher remanence, it requires a much larger coercive force to demagnetize them. That is, they have high coercivity. Neodymium magnets typically have around 1 to 1.3 tesla (10 – 13k Gauss). That’s about 3X the remanence value of ferrite magnets.
Coercive Force
Coercive force, or coercivity, refers to the measure or ability of a neodymium magnet to resist an opposing external magnetic field or other demagnetization forces like heat and alternating current. Basically, the higher the coercivity, the better.
Like there are different levels of heat resistance and performance losses in neodymium magnets, there are also coercivity levels. They are the “normal coercivity” (Hcb) and intrinsic coercivity (Hcj).
Hcb: is mostly called coercivity but, in some cases, normal coercivity. The amount of opposing external magnetic field is required to reduce the net flux density to zero.
When you expose a neodymium magnet to an opposing external field of this value, it loses its internal field and suffers reversible loss. The neodymium magnet will regain magnetism if the external force is removed because its polarity remains intact.
Hcj: is the intrinsic coercivity, and it is the point where a neodymium magnet suffers an almost permanent loss. Every neodymium magnet has an intrinsic coercivity value. Suppose you expose a neodymium magnet to an opposing external magnetic field equal to or higher than that value. In that case, the neodymium magnet will not recover even after removing the external magnetic field.
What happens here is that the external magnetic field not only reduces the internal field to zero it also reduces the polarization to zero. And for the neodymium magnet to become magnetic again, you will have to remagnetize it unless there has been physical damage, which may hinder it from becoming magnetized.
Temperature
Another essential metric to pay attention to when measuring the capabilities of your neodymium magnets is temperature. Temperature influences the performance of magnetic materials, including neodymium magnets. And the two terms you should pay attention to here are operating temperature and curie temperature.
The operating or working temperature describes the temperature range where a neodymium magnet can function correctly. The figure you should care about here is the max operating temperature or MaxOpTemp.
The max operating temperature describes the limit to which your neodymium magnet can get hot before it begins to suffer irreversible loss of magnetic force. The MaxOpTemp does not refer to the heat generated by the heat generator but the neodymium magnet’s temperature.
So, given enough time, it is possible to heat a neodymium magnet to its MaxOpTemp even when the available heat is within the operating temperature limit.
The Curie Temperature indicates how hot a piece of neodymium magnet can get before it permanently loses its magnetic force. I.e., it will not regain magnetism when it cools down and attempts to remagnetize it may fail.
Neodymium magnets’ curie temperatures are graded like maximum operating temperature, using letters after the neodymium magnet’s grade.
Neodymium magnets are popular due to their strength and durability. They can function for a long time and still not lose their magnetism.
Below are the max operating temperature and curie temperature of our neodymium magnets.
| Grade | Max Operating Temperature | Curie Temperature |
| N | 80°C or 176°F | 310°C or 590°F |
| M | 100°C or 212°F | 340°C or 644°F |
| H | 120°C or 248°F | 340°C or 644°F |
| SH | 150°C or 302°F | 340°C or 644°F |
| UH | 180°C or 356°F | 350°C or 662°F |
| EH | 200°C or 3922°F | 350°C or 662°F |
Where to Get Quality Neodymium Magnets?
ROBO Magnetic is available to help you design neodymium magnets for both custom and standard applications. Our engineers are certified professionals who use cutting-edge technology to deliver the best quality throughout the production process. As a company, we have nearly two decades of experience manufacturing neodymium magnets for businesses worldwide. Contact us today with your requirements for your next project.
