Pot magnets (also known as holding magnets) are available basically into three material types and there is a great variety of size available. 

1) Ferrite Pot Magnet - This material offers a good performance from an inexpensive magnet, however, they tend to be bulky and are not always suitable where space is an important factor. The steel parts are plated & the Ferrite is inert thus corrosion is limited. Maximum operating temperature is +120 C.