clearly not a surface defect. For some materials it can be due to dopants or 2nd phases (nano crystals for example within the matrix). they are many models which explains DMS. It really depends on which materials you are talking about and the dopant concentration...

http://www.amazon.com/Spintronics-Semiconductors-Semimetals-Tomasz-Dietl/dp/0080449565/ref=sr_sp-atf_title_1_1?s=books&ie=UTF8&qid=1392759246&sr=1-1

The magnetism in some compounds is really due to dopants, this is the case in GaMnAs, GaMnN, ZnCrTe,.... However , one should be careful, there are over-simplified theoretical approaches that lead to incorrect and misleading conclusions concerning its origin and nature: in reality in these systems TC do not increase with the carrier density , the couplings are not of RKKY form,..... one can find many papers discussing these apparent controversies,.. but there are situations where the origin may be attributed to other defects, vacancy for example or non magnetic dopant in some cases,...

@Georges Bouzerar: could you, please, give a link to one of these papers?

Thank you Georges Bouzerar ...........,

Dear Moritz, most of the manuscripts are accessible on research gate, otherwise you can download the papers on Arxiv or in the respective journals.

Dear Chithira, thank you for your positive feedback on my comment.