Magnets have come a long way since the days of your youth when you spent hours arranging those brightly-colored plastic alphabet magnets to your mom’s refrigerator door. Today’s magnets are stronger than ever and their variety makes them useful in a wide variety of applications.
Rare earth and ceramic magnets – especially large rare earth magnets – have revolutionized many industries and businesses by expanding the number of applications or making existing applications more efficient. While many business owners are aware of these magnets, understanding what makes them different can be confusing. Here’s a quick rundown of the differences between the two types of magnets, as well as a synopsis of their relative advantages and disadvantages:
These extremely strong magnets may be composed of either neodymium or samarium, both of which belong to the lanthanide series of elements. Samarium was first used in the 1970s, with neodymium magnets coming into use in the 1980s. Both neodymium and samarium are strong rare earth magnets and are used in many industrial applications including the most powerful turbines and generators as well as scientific applications.
Sometimes called NdFeB magnets for the elements they contain – neodymium, iron and boron, or just NIB – neodymium magnets are the strongest magnets available. The maximum energy product (BHmax) of these magnets, which represents the core strength, can be more than 50MGOe.
That high BHmax – roughly 10 times higher than a ceramic magnet – makes them ideal for some applications, but there is a tradeoff: neodymium has a lower resistance to thermal stress, which means that when it exceeds a certain temperature, it will lose its ability to function. The Tmax of neodymium magnets is 150 degrees Celsius, about half that of either samarium cobalt or ceramic. (Note that the exact temperature at which magnets lose their strength when exposed to heat can vary somewhat based on the alloy.)
Magnets can also be compared based on their Tcurie. When magnets are heated to temperatures exceeding their Tmax, in most cases they can recover once cooled; the Tcurie is the temperature beyond which recovery cannot occur. For a neodymium magnet, the Tcurie is 310 degrees Celsius; neodymium magnets heated to or beyond that temperature will not be able to recover functionality when cooled. Both samarium and ceramic magnets have higher Tcuries, which makes them a better choice for high-heat applications.
Neodymium magnets are extremely resistant to becoming demagnetized by external magnetic fields, but they do tend to rust and most magnets are coated to provide protection from corrosion.
Samarium cobalt, or SaCo, magnets became available in the 1970s, and since then, they’ve been used in a wide variety of applications. Although not as strong as a neodymium magnet – samarium cobalt magnets typically have an BHmax of about 26 – these magnets have the advantage of being able to withstand much higher temperatures than neodymium magnets. The Tmax of a samarium cobalt magnet is 300 degrees Celsius, and the Tcurie can be as much as 750 degrees Celsius. Their relative strength combined with their ability to withstand extremely high temperatures makes them ideal for high-heat applications. Unlike neodymium magnets, samarium cobalt magnets have good resistance to corrosion; they also tend to have a higher price point than neodymium magnets.
Made of either barium ferrite or strontium, ceramic magnets have been around longer than rare earth magnets and were first used in the 1960s. Ceramic magnets are generally less expensive than rare earth magnets but they are not as strong with a typical BHmax of about 3.5 – about a tenth or less than that of either neodymium or samarium cobalt magnets.
Regarding heat, ceramic magnets have a Tmax of 300 degrees Celsius and, like samarium magnets, a Tcurie of 460 degrees Celsius. Ceramic magnets are highly resistant to corrosion and usually do not require any protective coating. They are easy to magnetize and are also less expensive than neodymium or samarium cobalt magnets; however, ceramic magnets are very brittle, making them a poor choice for applications involving significant flexing or stress. Ceramic magnets are commonly used for classroom demonstrations and less powerful industrial and business applications, such as lower-grade generators or turbines. They may also be used in home applications and in the production of magnetic sheets and signage.
Post time: Mar-09-2022