What are Rare Earth Magnets?

We know magnets attract other magnetic materials. There are two types- permanent & temporary magnets. This session will cover rare earth magnets- a type of permanent magnet, in detail.

Rare Earth Magnets:

Rare-earth magnets are the strongest permanent magnets, made from alloys of rare earth elements, mainly from the lanthanide series. Developed in the 1970s and 1980s, they produce much stronger magnetic fields (over 1.4 Tesla) compared to other magnets like alnico and ferrite (0.5 to 1.0 Tesla).

There are two main types:

1. Neodymium magnets
2. Samarium–cobalt magnets

Another type, Terfenol-D, is used in audio systems due to its magnetostrictive properties (changes shape when magnetized).

Rare-earth magnets are fragile and prone to corrosion so they are often coated or plated for protection. Despite the name, rare earth elements are not actually rare and are as common as tin or lead.

Types of Rare Earth Magnets

There are two main types of rare earth magnets:

1. Samarium-Cobalt
2. Neodymium

Samarium-Cobalt Magnets

Samarium-cobalt magnets were the first rare earth magnets discovered. They are less commonly used than neodymium magnets due to their higher cost and weaker magnetic field strength. These magnets have a high Curie temperature and excellent resistance to oxidation, but they are fragile and can chip, crack, or crumble when exposed to thermal shock.

Advantages and Disadvantages:

Advantages	Disadvantages
High corrosion resistance	Expensive
High-temperature stability	Low mechanical strength
High coercive force	….

Neodymium Magnets

Discovered in the 1980s, neodymium magnets are the most affordable and strongest type of rare-earth magnet. They are made from an alloy of iron, neodymium and boron (NIB). Neodymium magnets have a high coercivity and are used in various applications such as electric motors, jewelry clasps, hard disk drives and magnetic hold-downs.

Advantages and Disadvantages:

Advantages	Disadvantages
High corrosion resistance	Expensive
High-temperature stability	Low mechanical strength
High coercive force	….

How Are Rare Earth Magnets Made?

Rare earth magnets are made from elements with atomic numbers between 57 and 71. Most common and strongest type is made from an alloy of neodymium, boron and iron.

Manufacturing Process:

Powder Production: Solid ingots of neodymium, boron, and iron are crushed and ground into a fine powder through three phases:

• Phase 1: Coarse particles are mechanically crushed.
• Phase 2: Particles are ground into finer grains.
• Phase 3: Particles are jet-milled into tiny spherical particles.

Molding: Powder is shaped into magnets using steel or rubber molds. For neodymium alloy- a process called isostatic pressing is used.

Magnetization: A magnetic field of about 4 Tesla is applied to give magnet its magnetic properties.

Sintering: The magnet is heated to 1000°C in a process called liquid phase sintering.

Coating: Finally magnet is coated to prevent corrosion. Common coatings include- gold, nickel, zinc, tin, or epoxy resin.

Strong & long-lasting rare earth magnets with numerous uses are product of this method.

Uses of Rare Earth Magnets

Common Applications:

Numerous common gadgets & technology include following that use rare earth magnets:

• Bicycle dynamos: Produce energy to run bicycle lights.
• Drills & screwdrivers are examples of power tools with cordless tool motors.
• Magnetic Resonance Imaging (MRI) Devices: Strong magnetic fields are produced by MRI devices to facilitate medical imaging.
• Audio Headphones: Provide strong magnetic fields for high-quality sound.
• High-Performance AC Servo Motors: Used in precision machinery and robotics.
• Computer Hard Disk Drives: Help in reading and writing data.
• Industrial Uses: Assist in product purity, equipment protection, and quality control.
• Wind Turbine Generators: Improve efficiency in generating wind power.
• Electric Vehicle Motors: Power starter-generators and traction motors.
• Fishing Reel Brakes: Enhance performance in fishing gear.

Other Applications:

• LED Throwies: Small magnetic LED lights for decoration.
• Roller Coasters: Use magnetic propulsion for thrilling rides.
• Electrodynamic Bearings: Reduce friction in machinery.
• Linear Motors: Power magnetic levitation trains.
• Electric Guitar Pickups: Capture string vibrations for sound.
• Stop Motion Animation: Create smooth animations with precision.
• Diamagnetic Levitation: Study interactions between superconductors and magnetic fields.
• Neodymium Magnet Toys: Offer fun and educational play.

Rare earth magnets are essential in both advanced technology and everyday items due to their strength and versatility.

Difference Between Rare Earth Magnets and Ceramic Magnets

Aspect	Rare Earth Magnets	Ceramic Magnets
Composition	Made from rare earth elements (e.g., neodymium, samarium-cobalt)	Made from iron oxide (ferrite) mixed with other materials
Magnetic Strength	Very strong, with fields greater than 1.4 Tesla	Weaker, with fields between 0.5 to 1.0 Tesla
Cost	Generally expensive	More affordable
Temperature Stability	Moderate, some are sensitive to high temperatures	Good, generally stable up to moderate temperatures
Corrosion Resistance	Low, often coated to prevent rust and damage	High, naturally resistant to corrosion
Mechanical Strength	Low, prone to chipping and cracking	High, more durable and robust
Common Uses	Electronics, motors, medical devices, high-performance applications	Toys, household items, some industrial uses

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More Details

Rare Earth Magnets:

• Strength: Known for their high magnetic strength and compact size.
• Applications: Used in advanced technologies like MRI machines, high-performance motors, and hard disk drives.
• Coating: Often coated with nickel, zinc, or epoxy to protect against corrosion and physical damage.
• Fragility: They are brittle and can break easily if dropped or subjected to stress.

Ceramic Magnets:

• Strength: Weaker than rare earth magnets, but still useful for many applications.
• Applications: Commonly found in refrigerator magnets, speaker systems, and low-cost industrial uses.
• Coating: Typically does not need additional coating due to its natural corrosion resistance.
• Durability: More durable and less likely to break under normal conditions compared to rare earth magnets.

This comparison should help you understand the differences and applications of each type of magnet.

FAQ

Why are rare earth magnets normally coated or plated?

Rare earth magnets are coated or plated because they are brittle and can easily break, chip, or crumble. Coating helps protect them from physical damage and corrosion, ensuring they stay intact and functional for longer.

Do neodymium magnets lose their strength over time?

Neodymium magnets do lose a small amount of their strength over time, but it is minimal. They typically lose less than 1% of their strength every 10 years.

What does “rare-earth” mean when discussing rare-earth metals?

The term “rare earth” can be misleading. While some of these metals are as abundant as tin or lead in the Earth’s crust, they are called rare because they are not evenly distributed. They are found in scattered, low-concentration deposits, unlike metals like coal or copper that exist in more concentrated seams.

Which is the strongest magnet in the world?

The strongest magnet in the world is made of neodymium. It is known for its exceptional strength compared to other types of magnets.

Are neodymium magnets sensitive to temperature?

Yes, neodymium magnets are sensitive to temperature. Excessive heat can demagnetize them, causing them to lose their magnetic strength.