Magnetocaloric　materials　can　be　useful　in　magnetic　refrigeration　applications,　but　to　be　practical　the　magneto-refrigerant　needs　to　have　a　very　large　magnetocaloric　effect　(MCE)　near　room　temperature　for　modest　applied　fields　(＜2　T)　with　small　hysteresis　and　magnetostriction,　and　should　have　a　complete　magnetic　transition,　and　environmentally　friendly.　One　system　that　may　fulfill　these　requirements　is　Mn2-xFexP1-yGey,　where　a　combined　first-order　structural　and　magnetic　transition　occurs　between　the　high　temperature　paramagnetic　and　low　temperature　ferromagnetic　phase.　We　have　used　neutron　diffraction,　differential　scanning　calorimetry,　and　magnetization　measurements　to　study　the　effects　of　Mn　and　Ge　location　in　the　structure　on　the　ordered　magnetic　moment,　MCE,　and　hysteresis　for　a　series　of　compositions　of　the　system　near　optimal　doping.　The　diffraction　results　indicate　that　the　Mn　ions　located　on　the　3f　site　enhance　the　desirable　properties,　while　those　located　on　the　3　g　sites　are　detrimental.　The　phase　fraction　that　transforms,　hysteresis　of　the　transition,　and　entropy　change　can　be　affected　greatly　by　both　the　compositional　homogeneity　and　the　particle　size,　and　an　annealing　procedure　has　been　developed　that　substantially　improves　the　performance　of　all　three　properties　of　the　material.　We　also　establish　a　correlation　between　applied　magnetic　field　to　complete　the　transition　and　the　temperature　range　of　coexistence　of　the　PM　and　FM　phase.　On　the　basis　of　these　results　we　have　identified　a　pathway　to　understand　the　nature　and　to　optimize　the　MCE　properties　of　this　system　for　magnetic　refrigeration　applications.　(C)　2016　Elsevier　B.V.　All　rights　reserved.