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Electrical detection of spin precession in freely suspended graphene spin valves on cross - linked poly ( methyl methacrylate ) .
 Chemical: graphene; Chemical: poly ( methyl methacrylate )
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: graphene; Chemical: poly ( methyl methacrylate )