Understanding the key properties of magnetic materials is essential for choosing the right magnet for your needs. In this blog, we explain five key magnetic properties:
By exploring these properties, we will provide insights into how different magnetic materials perform under various conditions, helping you make an informed decision when it comes to selecting the right magnet.
Remanence
Magnetic remanence refers to the magnetisation retained by a material after an external magnetic field is removed. If we think of a magnet as a sponge, remanence is like the water left in the sponge when it is fully saturated.
The remanence value is denoted by the symbol (Br). It is measured in units of tesla (T) or gauss (G), with 1 tesla being equal to 10,000 gauss.
In materials such as neodymium magnets, remanence is high. These magnets retain a significant level of magnetisation even after the magnetising field is removed. This characteristic makes them highly effective in applications requiring strong and enduring magnetic fields, such as in motors and lifting machinery.
Conversely, magnetic materials with low remanence lose their magnetisation quickly once the external magnetic field is removed. This proves useful in various applications: in transformers and inductors, it minimizes energy losses from hysteresis, thereby enhancing efficiency and preventing overheating. In hard disk drives, the low remanence of these materials in read-write heads allows for rapid and precise changes in magnetisation, crucial for maintaining data accuracy and preventing corruption.
It is important to note that while remanence influences a magnet’s surface magnetism, factors such as shape and size also play a role. For magnets with the same shape, performance, and size, a higher remanence indicates stronger magnetism. However, when comparing magnets of different shapes, properties, and sizes, Br value alone is not sufficient to compare surface magnetism.
Coercivity
Magnetic coercivity is a measure of a material’s resistance to demagnetisation, indicating the amount of reverse magnetic field required to reduce the material’s magnetisation to zero.
It is expressed in the SI system as amperes-per-meter (A/m) or kiloamperes-per-meter (kA/m) and in the CGS system as oersteds (Oe) or kilooersteds (kOe).
N.B: The SI system and CGS system are two sets of units used for measuring magnetic properties; the SI system is internationally standardised and widely adopted, while the CGS system is historically significant (used more commonly in the 19th and 20th century) and still used in some areas of physics for its simplicity in certain equations.
There are two types of coercivity:
- Intrinsic Coercivity (Hcj): The magnetic field required to reduce magnetisation to zero. This is more commonly used as it better represents the material’s resistance to demagnetisation.
- Normal Coercivity (Hcb): Less frequently used in practical applications, this is a measure of the magnetic field required to reduce the magnetic flux to zero.
Materials with strong coercivity, known as hard magnetic materials or permanent magnets, can withstand significant external magnetic fields without losing their magnetisation. Examples include neodymium, samarium cobalt, and alnico magnets.
These materials are stable in challenging environments and are used in applications where they must retain their magnetism despite fluctuating magnetic fields or high temperatures, as often required in industrial, automative and aerospace industries.
Materials with low coercivity – known as soft magnets – are easily demagnetised, making them ideal for applications requiring rapid polarity reversals, such as in transformer cores. These materials can undergo constant magnetisation and demagnetisation with minimal energy losses.
Magnets can be demagnetised by a variety of factors, including temperature, kinetic force and external magnetism. For instance, Neodymium magnets (NdFeB magnets) are extremely powerful but can become demagnetised at temperatures above 80°C. In high-temperature situations, samarium cobalt and alnico magnets are preferable due to their excellent resistance to demagnetisation, with working temperatures of up to 350°C and 550°C respectively.
Maximum Energy Product
Maximum energy product (also known as BHmax) is a key parameter for evaluating the strength and efficiency of a magnet. It represents the maximum amount of magnetic energy stored in the material, expressed in Mega Gauss Oersteds (MGOe) in the CSG system or kJ/m³ (Kilojoule per cubic meter) in the SI system.
A higher BHmax indicates a more powerful magnet capable of delivering greater performance. The higher the BHmax of the magnetic material, the smaller the magnet required for a particular application.
In practical terms, BHmax is crucial when designing magnetic circuits and devices. In electric motors, sensors and actuators, a higher maximum energy product means a smaller, more efficient and powerful magnet can be used, optimising the device’s performance and size.
Maximum Working Temperature
Maximum working temperature is the highest temperature at which a magnet can operate before it beings to irreversibly lose its magnetic properties. Beyond this temperature, the material’s magnetisation decreases significantly, and the magnet can become permanently demagnetised. It is crucial to take this into account when deciding what magnet best suits your needs.
The temperature at which a magnet will lose its magnetisation entirely is known as the Curie Temperature.
Different magnetic materials have varying maximum working temperatures. As we covered previously, neodymium magnets typically have a lower maximum working temperature compared to samarium cobalt magnets. Choosing the right magnet with an appropriate maximum working temperature is crucial for applications involving high temperatures, such as in aerospace, automotive, and industrial environments.
Temperature Coefficient
The temperature coefficient is a measure of how a magnetic material’s properties change with temperature, specifically indicating the rate at which the material’s magnetic strength decreases as the temperature increases.
Temperature Coefficient is typically expressed as a percentage per degree Celsius (%/°C) and can affect both the remanence and the coercivity of the magnet.
Materials with a low temperature coefficient maintain their magnetic performance more consistently across temperature variations, making them suitable for applications that involve fluctuating or high temperatures.
Get In Touch with Goudsmit UK
Understanding the magnetic properties of remanence, coercivity, maximum energy product, and maximum working temperature is essential for selecting the right magnet for your specific needs. At Goudsmit UK, we offer a wide range of high-quality magnets designed to meet diverse applications and environments. Our team of experts is always ready to help you choose the best magnetic solution, ensuring optimal performance and longevity for your projects.
For more information on our magnetic products and services, please contact us directly. Let Goudsmit UK be your trusted partner in all things magnetic!
