This　work　demonstrates　that　Mn　can　be　a　beneficial　candidate　for　the　performance　modulation　of　permanent　magnetic　materials　like　SmCo5.　Theoretical　calculations　reveal　that　Mn　has　a　large　positive　contribution　to　the　magnetization　of　SmCo5,　owing　to　the　strong　ferromagnetic　exchange　interaction　between　Co　and　Mn　atoms.　It　is　also　found　that　Mn　could　occupy　both　2c　and　3g　crystal　sites　because　of　the　minute　energy　difference　between　them　can　be　easily　overcome　through　thermal　activation.　Co　atoms　on　the　same　site　with　Mn　have　increasing　moments　with　the　increase　in　Mn　content,　whereas　those　on　the　other　sites　show　decreasing　moments.　The　experimental　substitution　of　Mn　for　Co　leads　to　a　contraction　of　the　SmCo5　single-phase　region,　and　thus　pure　Sm(Co,　Mn)5　phase　could　only　be　obtained　through　subtle　control　of　Sm　content　by　annealing.　Significantly,　a　13　%　increase　in　saturation　magnetization　of　SmCo5　is　achieved　through　Mn　substitution.　A　slight　rise　in　the　Curie　temperature　is　also　obtained,　suggesting　that　Mn　substitution　does　not　strongly　disturb　the　exchange　interactions　of　the　Co　sublattice.　This　study　offers　a　new　option　for　enhancing　magnetic　properties　in　Sm–Co　systems　and　introduces　novel　physical　phenomena　resulting　from　Mn　substitution,　which　is　worthy　of　further　investigation.　©　2024　Elsevier　Ltd