Peculiar Rare Earth Magnets

Do you ever wonder what is a “material” made up of? Material is a structural composition of atoms and molecules whose structure is defined by magnetic action. Hence, we can define a material as some type of magnetic composition; one of the most commonly known magnets is the Rare earth magnet. The story started in early 1970s/80s when these rare earth magnets were first produced from alloys of rare earth elements. These are categorized under strong permanent magnets that produce comparatively stronger magnetic fields as compared to other magnets like alnico or ferrite.
How do you interpret these magnets from their name “rare earth magnets”? Actually the term is a misnomer as these metals are not rare, they are rather found abundant. These are formed from the earth elements that are ferromagnetic in nature. Ferromagnetic metals are those that have the capability to be magnetized only when they are exposed to low temperature conditions. In terms of the strength of magnetic field produced by these magnets, these strongest type of permanent magnets can have strong magnetic fields of 1.4 tesla as compared to others like ceramics that produce fields of only 0.5 to 1 tesla.

Peculiar behavior of rare earth elements:
These metals are ferromagnetic, like iron they can be permanently magnetized, with their curie temperature much below the room temperature which means that in pure form their magnetic behavior can be seen only at low temperatures. But they do possess the ability to form compounds with iron and nickel, also known as transition metals, and few of these compounds have their curie temperature more than the room temperature. Due to their crystalline structure, they have high magnetic anisotropy which means that a single crystal of this metal can be easily magnetized in one direction and will resist getting magnetized in any other direction. This results in high field strength of the magnets.

Types of rare earth magnets:
These high strength magnets can be broadly classified under two types Magnets: Neodymium Magnets and Samarium Cobalt magnets. Talking about Neodymium magnets, they were first invented in 1980s. These are the most affordable and the strongest type of rare earth magnets ever known. Composition wise these are made of neodymium, boron and iron. These three metals combine to form a tetragonal crystalline structure which is the strongest type of structure of permanent magnet ever made. Because of this brilliant feature, they have replaced many other types of magnets used in numerous applications and products. Products that need strong and permanent magnets like hard disk drives make use of these neodymium magnets.

What makes Neodymium magnets so popular?
These rare earth metals are the most affordable type of magnets and can be used in applications that need strong, compact and permanent magnets. The credit also goes to another brilliant feature that these metals possess – high coercivity, also known as the coercive force, which is the measure of ferromagnetic material to bear any external force like electric or magnetic field. Although they are vulnerable to oxidation process, use of protective treatments like metal plating (gold, nickel, tin and so on) can prevent the surface of the metal from getting corroded. Considering the cost factor, initially the high cost of these metals restricted their use to applications that require high field strength but with time the cost has reduced so much that these can now be used extensively in various sectors such as magnetic toys. Listing the magnetic properties of the permanent magnets we have:
• Remanence – This defines the measure of strength of the magnetic field. Neodymium magnets have high value of remanence.
• Coercivity – This measures the material’s resistance in the process of demagnetization. Neodymium magnets have much higher value of coercivity as compared to samarium cobalt magnets.
• Energy Product – this tells us the density of the magnetic energy possessed by the metal. Neodymium has high energy product.
• Curie temperature – this is the amount of temperature at which the material loses its property of being magnetic. Neodymium magnets have lower value of Curie temperature.
Cons of Neodymium rare earth metals:
These rare earth metals have some of the amazing features which have made them quite popular in various industries but apart from these Pluses, there are certain hazards of using these metals which can’t be seen with other type of permanent magnets. These hazards are mainly because of the great force implemented by these metals. If these metals are not restricted to get too close to each other with enough force, these can shatter and chip the brittle material and can cause injuries too. These have been incidents when kids who swallowed these magnets were affected in such a way that it lead to death. The high strength of magnetic field can prove to be harmful to various mechanical and electronic devices as they can remove the information in magnetic media like swipe cards, credit cards, floppy drives, and other devices.

Applications of neodymium magnets:
After having learnt the pluses and minuses of these magnets, what can you think about their applications? Well, the pluses have overshadowed the few cons of these magnets and hence these have replaced other ferrite magnets in many of the appliances that make use of latest technology. Their marvelous strength has permitted the use of small and light magnets for the tools that need strong permanent magnets. Now -a -days these are being used in Magnetic resonance Imaging, magnetic guitars, loudspeakers, headphones, electric motors like servo motors, cordless motors, electric power steering, electric generators and the list goes on. Apart from all these appliances, the great magnetic strength of these neodymium rare earth magnets has provided inspiration to many new applications where magnetic energy was not being used previously. To quote a few examples we have magnetic jewelry clasps, kids’ magnetic buildings and other magnetic toys. These strength and homogeneity of these metals have opened the doors in the medical sector as well where now these can be used in open MRI scanners which are used to scan the body.
Not even this, the US department of energy has recognized these rare earth magnets to be used in critical technologies and have started funding for a program titled as REACT that stands for Rare Earth Alternatives in Critical Technologies.

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