Neodymium magnets, also called Rare Earth Element or REE Magnets, are valued for their strength, luminescence and – of course- magnetic properties. The two most common rare earth elements in the magnetic industry are neodymium and samarium. The term rare earth magnets refers to two types of magnets: neodymium iron boron (NdFeB) and samarium cobalt (SmCo) magnets. Magnets are commonly used to secure a geocache to an appropriate surface (e.g. nanos), keep a geocache closed, in a locking mechanism of a gadget cache, or as a retrieval tool.
Commercially available neodymium magnets range from N35 to N55 grade, which basically reflects the maximum pull strength of the magnet. A N55 grade magnet is approximately 50% stronger than an N35 magnet of the same size.
Rare-earth magnets are extremely brittle and also vulnerable to corrosion, so they are usually plated or coated to protect them from breaking, chipping, or crumbling into powder; however, better to have them protected from the elements when using them in a geocache.