▁energy ▁product ▁B · H ▁of ▁ne od ym ium ▁magnet s ▁is ▁about ▁ 1 8   times ▁greater ▁than ▁" ordinary " ▁magnet s ▁by ▁volume . ▁This ▁allows ▁rare - ear th ▁magnet s ▁to ▁be ▁smaller ▁than ▁other ▁magnet s ▁with ▁the ▁same ▁field ▁strength . ▁ ▁Mag net ic ▁properties ▁ ▁Some ▁important ▁properties ▁used ▁to ▁compare ▁permanent ▁magnet s ▁are : ▁rem an ence ▁( Br ), ▁which ▁measures ▁the ▁strength ▁of ▁the ▁magnetic ▁field ; ▁co erc ivity ▁( H ci ), ▁the ▁material ' s ▁resistance ▁to ▁becoming ▁dem agnet ized ; ▁energy ▁product ▁( B · H max ), ▁the ▁density ▁of ▁magnetic ▁energy ; ▁and ▁Cur ie ▁temperature ▁( TC ), ▁the ▁temperature ▁at ▁which ▁the ▁material ▁los es ▁its ▁magnet ism . ▁R are - ear th ▁magnet s ▁have ▁higher ▁rem an ence , ▁much ▁higher ▁co erc ivity ▁and ▁energy ▁product , ▁but ▁( for ▁ne od ym ium ) ▁lower ▁Cur ie ▁temperature ▁than ▁other ▁types . ▁The ▁table ▁below ▁comp ares ▁the ▁magnetic ▁performance ▁of ▁the ▁two ▁types ▁of ▁rare - ear th ▁magnet s , ▁ne od ym ium ▁( N d 2 Fe 1 4 B ) ▁and ▁sam arium - c ob alt ▁( Sm Co 5 ), ▁with ▁other ▁types ▁of ▁permanent ▁magnet s . ▁ ▁Source : ▁ ▁Types ▁ ▁Sam arium - c ob alt ▁▁ ▁Sam arium – c ob alt ▁magnet s ▁( chem ical ▁formula : ▁Sm Co 5