What is Remanence(Br)?

Have you ever wondered what makes a neodymium magnet a strong magnet?

There are three significant properties to consider. One of the three is curie point (Tc) – the transition temperature for neodymium magnets to change magnetic properties. Another property is coercivity (Hc) which measures the resistance of the neodymium magnet to demagnetization. The third property is remanence(Br), which we’ll be learning more about today.

The Concept of Remanence (Br)

Remanence is the magnetism remaining after removing it from a successful magnetization while no longer being under any external magnetic influence. Simply speaking, it’s what’s left of the magnetic force even after removal. Retentivity, residual induction, or remaining flux density are used as alternatives to remanence. Remanence is usually represented by the symbol Br while its units are in either Gauss(Gs) or Tesla(T). Gauss is the CGS unit of magnetic flux density. It is equivalent to 1 Maxwell per centimeter square. Tesla is the SI unit equivalent to 1 Weber per meter square. The corresponding value for these units is 10,000 Gs per 1 T. Furthermore. Tesla can also be derived by dividing 1 Newton(N) by a current in Amperes(A), then multiplying it in meters (m). (1 Tesla = 1 Newton(N)/Current(A) x Meter(m)). Both Gauss and Tesla are vector quantities; this means they measure in a three-dimensional unit system.

Values of remanence have a direct correlation with magnetic flux density. A direct correlation indicates that a higher remanence value indicates a higher amount of magnetic flux density. So, a neodymium magnet with 1000 Gs has more remanence than a neodymium magnet with 100 Gs. Neodymium magnets that have high remanence values are referred to as hard neodymium magnets. They are usually categorized when the inherent coercivity values exceed approximately 10 kiloAmpere per meter. Hard neodymium magnets do not easily magnetize or demagnetize. Because of this, they are usually used for and are suitable materials for making permanent neodymium magnets—alloys of neodymium, iron, and boron compromise this specific type of magnet. Permanent magnets, on the other hand, are types of magnets that create their magnetic field. Examples of permanent magnets are neodymium magnets. They have the highest magnetic properties in the category of permanent magnets. The high remanence of neodymium magnets makes it a go-to magnet for many technical, industrial, and commercial applications.

Consequently, magnets that have low remanence are soft. Their magnetic fields are reversible and can easily be magnetized and demagnetized. The main difference between permanent and temporary magnets is the generation and remanence. Permanent neodymium magnets can create their magnetic field and retain it. Meanwhile, temporary magnets can only attach to something when a magnetic field is externally emitted. Thus, a withdrawn magnetic field makes it lose its attachment. So, soft magnets are best used as temporary magnets. Electrical equipment like switching circuits and generators commonly utilize these types of magnets. An excellent example of a soft magnet is iron. Iron can easily be attracted and removed to the point that it can be dusted or flicked off from where it is magnetized.

A neodymium magnet’s remanence should be considered when canvassing for its uses. However, we should never forget that other factors like temperature and conditions may disrupt the magnetic field. While remanence is directly related to magnetic flux density, it is inversely related to temperature. This means that when temperature increases, remanence decreases. Another factor we should consider checking when checking for a neodymium magnet’s quality and remanence is erosion and oxidation. A humid area can induce oxidation and corrosion. These events can lessen and worsen the performance of a neodymium magnet.

Moreover, it’s essential to determine where the neodymium magnet should be used. If a neodymium magnet should be exposed heavily or consistently to collision, then temporary neodymium magnets might not be the best option. Applying these concepts in the industrial setting can affect many more factors and may even have a ripple effect wherein one factor affects another. Therefore, remanence measurement and determination should always be tied with their practical uses when looking for a neodymium magnet.

Today, hard and permanent neodymium magnets are more utilized. The growing consumer electronics and motors market has significantly demanded them, especially neodymium magnets. Although there is still a great demand for soft and temporary neodymium magnets, the gap between their demands widens as we continue moving forward on the path of innovation and technology.

How is Magnetic Remanence Measured?

Measuring a neodymium magnet’s remanence requires professional instruments to draw the neodymium magnet’s hysteresis curve. A hysteresis curve or loop is a graph that shows the relationship between the induced magnetic flux density and the magnetic force. Three instruments can measure remanence: Field indicators, Gauss meter, and Tesla meter.

• Field Indicators

Due to their limited range, field indicators are most suitable for detecting the magnetic field that remains after demagnetization. Small mechanical devices called field indicators to use a soft iron vane that is redirected by a magnetic field. The scale’s pointer is rotated and moved by the vane, fastened to a needle. Field indicators can be calibrated and altered to provide quantitative information. However, the device’s mechanics typically limits field indicators’ measuring range. The measurement range of the one below is plus 20 Gauss to minus 20 Gauss.

• Gauss meter

A Gauss Meter, formerly known as the Gauss Magnetometer, is a device used to measure the magnitude and direction of relatively small magnetic fields. It comprises a meter, a cable that connects the meter, and an essential part of the Hall probe, the Gauss Meter. Named after the Hall effect that Edwin Hall discovered in 1879, the meter utilizes the probe to send current through the cable, and voltage is produced, then measured and recorded by the meter.

• Tesla meter

Tesla meters, on the contrary, measure larger magnetic fields and use the larger quantity SI measurement, as compared to the metric system of measurement used in Gauss meters (1 Tesla = 10,000 Gauss units). Although the Tesla meter differs from the Gauss meter with the measurement system used by the device, both have similar components and working principles by using the Hall effect, which refers to the movement of charge in a conductor in the direction of a magnetic pull.

Relationship between Remanence and Coercivity

After reaching magnetic saturation following the removal of an external magnetic field, the remaining amount of magnetization at zero driving field refers to remanence. The remaining magnetic field must be driven back to zero by an opposite driving field. This is where coercivity comes in because coercivity refers to the specific amount of reverse field required to push magnetization back to zero after reaching the material’s maximum magnetic strength. Vital measurements for remanence and coercivity make up the characteristics of permanent neodymium magnets because of their strong magnetism. Motors and magnetic storage media, including hard disks and tapes, conventionally utilize these times of neodymium magnets.

Relationship between Remanence and Surface Magnetism

Surface magnetism refers to the magnetic field strength on a particular point on a ferromagnet’s surface wherein Gauss (Gs) or Tesla (T) is used as the unit for measurement. While remanence can be used to determine the surface magnetism of a ferromagnet, it can only apply to a certain extent because surface magnetism can also differ depending on the physical properties of a magnetic material. For instance, the neodymium magnet with a higher remanence will be the stronger neodymium magnet between two neodymium magnets of the same shape, size, and magnetism. On the other hand, in comparing two neodymium magnets with different shapes, sizes and magnetism, surface magnetism will vary and cannot simply be used to determine remanence magnitude.

Relationship between Remanence and Magnetic Flux

Regardless of their shape, all neodymium magnets will have two magnetic poles that will generate magnetism and create a chain of organized and balanced patterns of invisible lines called magnetic flux, collectively called a magnetic field. The core is considered magnetized upon reaching magnetic saturation due to the magnetic flux density acting on the magnetic core. Once the external magnetic field is removed, the magnetization does not entirely return to zero or their neutral starting positions. Instead, the magnetism will remain at its remanent value before removing the external magnetic force.

Conclusion

Remanence is a significant factor in measuring neodymium magnet quality. As neodymium magnets become more and more utilized because of modernization, it is crucial to know how their remanence affects their applications, especially for industries that rely heavily on a neodymium magnet’s strength & magnetization, and demagnetization.

A neodymium magnet’s remanence is correlated with many things and can be made better or worse depending on its relationship with other factors. The diversity of remanence in different neodymium magnets helps us progress and innovate. As we advance, there has been an increase in demand for neodymium magnets with higher remanence. This demand is best exemplified in the production of neodymium magnets, where it was mentioned that they had become the go-to neodymium magnet for industries. They have become one of the most desirable neodymium magnets for commercial applications and have since become the standard for their uses.