Magnets are an exciting thing for all of us. We have seen it one form or the other in our lives. The magnets kept in our Physics laboratories did intrigue us when we had to do experiments. But these magnets are tied to us in more ways than we ever thought of. Everything from motors to the metal detectors of our malls, use some kind of magnet or the other. A commonly used variety of magnets are the rare earth magnets which were developed in the 1980’s. Among them, the Neodymium is the most popular rare earth magnets that are used these days. So, let us know a little more about this magnet.
What are the Neodymium Magnets?
The Neodymium magnet is a form of the permanent magnet that is derived from an alloy made from using rare earth elements. It is the most widely used rare earth magnet because of its affordability and strength of the magnetic field. The alloy contains Neodymium, iron, and boron which form the tetragonal crystal structure of Nd2Fe14B. The magnet was first discovered by General Motors and Sumitomo Special Metals in 1982. Microcrystalline grains form the alloy which allows the magnet to become aligned so that it may have a powerful magnetic field. The magnetic energy value of a Neodymium Magnet is about eighteen times more than the normal magnets in volume.
How are the Neodymium Magnets made?
The classical powder metallurgy or the sintered magnet process: In this type of production the base materials of the magnet are treated in a furnace and then set into moulds to form ingots. Then they are transformed into a powder which is sintered into dense blocks. Then they are treated with heat and cut into shapes so that they can become magnetized. But a new technique was devised in 2015 where the alloy may take a clay-like structure and then it can be made into different shapes and sizes before magnetization.
The Rapid solidification or the bonded magnet process: This is another process in which the melt spinning method is utilized on a thin strip of the NdFeB alloy to form the magnet. Then they are made into particles and a polymer is added to it to inject them into bonded moulds. They have low flux intensity but they easily take difficult shape.
The Neodymium magnets come in different grades. The grades depend upon the magnetic flux output that it has on per unit volume. Higher the values, higher the strength of the magnet. It mainly ranges from N35 to N 52. These types of magnets are used in every sphere of life. The most common usages of the Neodymium magnets are in computer hard disks, locks, loudspeakers, electrical motors, cordless tools, voice coils etc.
These days the magnets are also widely used in things like jewelry clasps, children’s toys, and MRI scans. So, it is an important discovery in the field of magnets. The world produces more than 80,000 tonnes of the Neodymium magnet to make our lives easier.
Rare earth magnets are one of the strongest magnets which are commercially available on earth and as a type of it, neodymium magnets are also useful in many purposes, so much so that it is generally believed that earth’s technology would have been a good two or three decades behind of this magnet wasn’t invented. So let’s check how and why this type of magnet is better than others:
Relative strength: The strength of a magnet’s magnetic field is measured with BHmax, so the higher the BHmax, the more powerful the magnet. Ceramic magnets contain a BHmax of 3.5 whereas the two rare earth types called samarium cobalt contains a BHmax of 25 and Neodymium contains a BHmax of 40. So ceramic magnets are around 10 times weaker than permanent magnets. Also because of its strength, handing permanent magnets over 2″ required caution.
Relative resistance to thermal stress: It should be noted that magnets tend to lose their strength and other properties when heated above their Tcurie temperature. Ceramic magnets have a Tcurie of 460 degree Celsius whereas samarium and neodymium have a Tcurie of 750 and 310 respectively. But if they are cooled below their top temperature, called Tmax, then they can regain their properties. So in lieu of this, ceramic magnets have a Tmax of 300 degree Celsius whereas samarium cobalt and neodymium magnets have a Tmax of 150 degree Celsius.
Relative durability: Neodymium magnets are brittle and as a result are difficult to use. On top of this, it also corrodes easily. SmCo or samarium cobalt magnets are slightly less brittle and are also corrosion resistant. Ceramic magnets provide good resistance to both corrosions as well as demagnetization.
Cost: Ceramic magnets are less costly than both SmCo and NdFeB (neodymium) magnets.
So these two magnets are used in different applications. Like ceramic magnets are used in fridges or in stereos whereas rare earth and neodymium magnets are used in generators, levitation machines, jewellery, hard disk drives, motors and more. Both of them are useful in their own unique way and so these above properties should be kept in mind while choosing which magnet to go for.
Before exploring the applications of rare earth and neodymium magnets, it’s time to know what exactly these magnets are. First of all, neodymium magnets are a type of rare earth magnets. They are called rare earth because they are made up of the lanthanide. These are the strongest and permanent magnets which are commercially available in the world. Their features include:
Unparalleled levels if magnetism
Resistance to demagnetization (when compared to other magnets like alnico, ferrite and even samarium cobalt ones)
These magnets are so strong that even tiny ones are effective so much so that a magnet just 5mm long and 8mm in diameter can generate a force of above 1,700 grams in spite of weighing only 2 grams. So with these properties, all available in pocket sizes, there are bound to be major users of this substance, like:
Hard disk drives: Hard disk drives record data by constantly magnetizing and demagnetizing a thin film of ferromagnetic material present on the disk. Apart from this, each disk is also divided into sectors and each sector contains numerous individual magnetic disks which are magnetized when the read or write head of the drive is written to the drive.
Audio Equipment: In speakers, these permanent magnets are used right alongside a current carrying coil which assists in changing electricity into mechanical energy. For microphones, the reverse is applicable- the permanent magnet creates a magnetic field, which allows the coil to move through it, thus producing an electrical signal which is similar to the original sound made.
Dentures: This might come as a surprise but neodymium magnets are useful in holding together replacement dentures in case of several missing teeth.
Door catches: Neodymium magnets are pretty widely used in various residential, commercial and public building to make magnetic door catches. These magnets hold the weight of the door quite easily and with the help of the leverage provided by the door, it results in the magnets being easily separated.
Generators and motors: These two work in reverse, as in electric motors are dependent upon a combination of an electromagnet and a neodymium magnet to convert the electric energy into a mechanical one. As said above, the opposite is true for the generator.
MRI scanners: This is pretty obvious as MRI scanners generate a huge magnetic field which aligns the protons present in the human body in the direction if the magnetic field.
ABS system sensors: ABS or anti-lock braking sensors uses rare earth magnets but wrapped up inside copper coils. A sensor is positioned close to the ABS reluctor ring and as the ring revolves, a voltage is introduced in the copper wire. This signal is then monitored by the computer system of the vehicle and thus used to define wheel speed.
Apart from this, they are used in lifting machinery, jewelry, bearings, levitation machines and more. In fact, these are so widely used that it is commonly regarded that without this magnet; our world would be two or three decades behind on technological advancement.