Metal found by graduate in young horse (6)
I believe the answer is:
cobalt
'metal' is the definition.
(I know that cobalt is a type of metal)
'graduate in young horse' is the wordplay.
'graduate' becomes 'BA' (someone with a Bachelor of Arts degree).
'in' means one lot of letters goes inside another.
'young horse' becomes 'colt' (I've seen this before).
'ba' inserted inside 'colt' is 'COBALT'.
'found by' is the link.
(Other definitions for cobalt that I've seen before include "Deep blue colour" , "Metal giving its name to type of deep blue" , "Metal element" , "Magnetic metal" , "given radiotherapy with this?" .)