Magnetic and structural results on (Mn,Co)3(Si,P) and (Fe,Co)3(Si,P) alloys

•A new system with remarkable properties for inverse magnetocaloric effect applications was discovered.•Co content and the transition temperature limits of the (Fe,Co)2P system described in previous papers appears to be faulty.•Quaternary samples belonging (Fe,Co)3(Si,P) and (Mn,Co)3(Si,P) systems are not present a single phase. A systematic study of the (Fe,Co)3(Si,P) and (Mn,Co)3(Si,P) systems was performed. Although both these quaternary systems proved they do not exist as single phase compounds, a great deal of new information and results was generated about them. Previously reported value for transition temperatures and compositional limits have been found to be incorrect for the (Fe,Co)3P system and a novel inverse magnetocaloric effect compound has been discovered as a consequence of the study performed in the (Mn,Co)3(Si,P) system.