In　this　paper,　we　studied　the　magnetic　hardening　mechanism　of　SmCo6.6Nb0.4　nanoflakes　prepared　by　surfactant-assisted　high　energy　ball　milling.　The　hysteresis　loop　with　the　initial　magnetization　curve　and　the　corresponding　differential　susceptibility　curve　of　thermally　demagnetized　SmCo6.6Nb0.4　nanoflakes　were　studied.　It　is　concluded　that　the　magnetization　reversal　process　of　the　specimen　is　determined　by　domain　wall　motion,　i.e.,　the　magnetic　hardening　mechanism　of　the　magnetic　powders　is　dominated　by　domain　wall　pinning.　Moreover,　the　dependence　of　coercive　field　of　the　nanoflakes　on　the　maximum　applied　field　derived　from　minor　hysteresis　loops　also　confirms　the　pinning　effect　in　the　magnetization　reversal.　(C)　2014　AIP　Publishing　LLC.