Demagnetiser smashed in quarrel (12)
I believe the answer is:
disagreement
'quarrel' is the definition.
(I've seen this before)
'demagnetiser smashed' is the wordplay.
'smashed' indicates anagramming the letters.
'demagnetiser' is an anagram of 'DISAGREEMENT'.
'in' acts as a link.
(Other definitions for disagreement that I've seen before include "Contretemps" , "Quarrel" , "Difference of opinion" , "Conflict" , "Lack of consensus" .)