A magnet is defined as an object or piece of material which generates a magnetic field. The magnetic field is moving electrical charges that cause other magnetic objects to either be attracted to or repelled from the magnet. Magnets come in a variety of types, with varying degrees of magnetic strength, resistance to heat, permanence, and tolerance of corrosion.
Magnets can basically be categorized in two ways: permanent and non-permanent. Non-permanent magnets are electromagnets, meaning an external source of power is required to electrically trigger them to be magnetic. Electromagnets are used in numerous industrial applications, including solenoid valves, biomagnetic separation, AC and DC motors, and electric transformers.
Ceramic or ferrite magnets, alnico magnets, and rare earth magnets fall under the category of permanent magnets. Ceramic magnets have a low amount of magnetic power. They are very brittle and are more easily prone to breakage compared to other magnets. Despite this, ceramic magnets are very cost-effective, and are used in applications such as magnetic tools, magnetic chucks, and motors.
Rare earth magnets are much less cost effective to manufacture than ceramic magnets. However, they are much more powerful and are much more likely to retain their magnetism. Rare earth magnets are utilized as industrial magnets, and are used for applications including MRI’s, testing, sensors, speakers, motors, holding, and lifting.
A tool or system that utilizes ceramic magnets, electromagnets, alnico magnets, rare earth magnets, or a combination to perform a specific type of function is known as a magnetic assembly. Magnetic assemblies are used to do specific kinds of holding, lifting, or separation of magnetic materials. The force of the magnetic assembly can be increased by combining certain types of magnets in assemblies.
Magnetic assemblies can be commonly found in the industrial and manufacturing field. The functions they perform include mounting, holding, water treatment, and the lifting of sheet metals and metal parts. Other industries that extensively use magnetic assemblies are electric motor activation, blood testing and separating, linear actuators, ignition timing systems, power meters, welding equipment, TV monitors, sensors, sound speakers, MRI’s, automotive, electronics, biomedical, aerospace, and film and software disk programming and erasing.
There are some types of magnets that are relegated to a specific industry or application. For example, in the automotive and consumer industries, sheet magnets are commonplace. Sheet magnets are flexible and composed of a ferrite and plastic composite which is extruded into a magnetic sheet and can be cut into magnetic strips of rubber material. The most common magnet is the bar magnet, which is also made from a ferrite metal material.
There are several properties that magnet manufacturers take into consideration when fabricating magnets. These properties are porosity, ease of fabrication, magnetic retention under heat and corrosion, magnetic strength, and cost. Different types of permanent magnets are made from a variety of materials and will have their own set of characteristics.
There is not a magnet out there that has all of the characteristics listed above. Ceramic magnets are made from a sintered powder composite of iron oxide, ceramic powder, and either barium or strontium. Ceramic magnets can be extruded, compressed, or sintered into a multitude of shapes. The combination of these materials makes a ceramic composite that is charcoal gray in color, porous, brittle, and cost-efficient.
Alnico magnets are slightly more expensive, and are made from a composite of cobalt, iron, aluminum and nickel. Although they are similar to ceramic magnets, Alnico magnets are less brittle, have higher magnetic resistance, and can be more easily shaped.
Rare earth magnets are more powerful than ceramic or alnico magnets. Types of rare earth magnets include samarium cobalt magnets and neodymium magnets. The elements samarium and neodymium contain outer f-electron shells that are partially filled, and act as a powerful source behind their magnetic fields.
Neodymium magnets have a stronger magnetic pull than any other type of magnet. These magnets are made from a composite of boron, iron, and neodymium. Despite their powerful magnetic force, they are much less resistant to heat and corrosion. Samarium cobalt magnets are made of a combination of cobalt and samarium, and are known for their high resistance to corrosion and demagnetization.
Another key characteristic is that is has a thermal stability of up to 550 degrees Celsius. Therefore, samarium cobalt is used in applications that involve exposure to extreme heat, like medical tools and motors. Finally, neodymium magnets are harder than ceramic magnets, and are coated with nickel for protection due to its brittle nature.
Rare earth magnets are typically costlier than their non-rare-earth counterparts due to the scarcity of rare earth materials and the lengthy process of the extraction of the materials from lanthanide ores.