▁or ▁cer am ic ▁magnet s ▁typically ▁exhib it ▁fields ▁of ▁ 0 . 5 ▁to ▁ 1 ▁t es la . ▁ ▁There ▁are ▁two ▁types : ▁ne od ym ium ▁magnet s ▁and ▁sam arium – c ob alt ▁magnet s . ▁ ▁R are - ear th ▁magnet s ▁are ▁extremely ▁brit t le ▁and ▁also ▁vulner able ▁to ▁cor ros ion , ▁so ▁they ▁are ▁usually ▁pl ated ▁or ▁co ated ▁to ▁protect ▁them ▁from ▁breaking , ▁ch ipping , ▁or ▁cr umb ling ▁into ▁pow der . ▁ ▁The ▁development ▁of ▁rare - ear th ▁magnet s ▁began ▁around ▁ 1 9 6 6 , ▁when ▁ ▁K . ▁J . ▁Str nat ▁and ▁G . ▁Hof fer ▁of ▁the ▁US ▁Air ▁Force ▁Material s ▁Labor atory ▁discovered ▁that ▁an ▁al loy ▁of ▁y tt rium ▁and ▁c ob alt , ▁Y Co 5 , ▁had ▁by ▁far ▁the ▁largest ▁magnetic ▁an is ot ropy ▁constant ▁of ▁any ▁material ▁then ▁known . ▁ ▁The ▁term ▁" rare ▁earth " ▁can ▁be ▁mis leading , ▁as ▁some ▁of ▁these ▁met als ▁can ▁be ▁as ▁abund ant ▁in ▁the ▁Earth ' s ▁cr ust ▁as ▁tin ▁or ▁lead , ▁ ▁but ▁rare ▁earth ▁or es ▁are ▁une ven ly ▁distributed , ▁not ▁existing ▁in ▁se ams ▁like ▁coal ▁or ▁co pper , ▁so ▁in ▁any ▁given ▁cub ic ▁kilomet re ▁of ▁cr ust ▁they ▁are ▁" rare ". ▁The ▁major ▁source ▁is ▁currently ▁China . ▁Some ▁countries ▁class ify ▁rare