  We report the magnetic changes from canted antiferromagnetic to ferromagnetic
orderings in anti-115-type MnPt$_{5-x}$Pd$_x$P ($x$ = 1, 2, 2.5, 3, 4, and 5)
and the discovery of a new rare-earth-free ferromagnet, MnPd$_5$P by both
theoretical prediction and experimental investigation. The family compounds
were synthesized using high temperature solid state method and characterized to
crystalize in the anti-CeCoIn$_5$ type with the space group P4/mmm exhibiting a
two-dimensional layered structural feature. The magnetic property measurements
indicate that the compounds ordered from canted A-type antiferromagnet in
MnPt$_5$P to ferromagnet above the room temperature with varying degrees of
coercivity and magnetic moments in MnPd$_5$P by reducing the spin orbital
coupling. The results of the MnPt$_{5-x}$Pd$_x$P have been analyzed in
comparison to the other candidates of the 151 family of Mn(Pt/Pd)$_5$(P/As) to
understand the complex structure-magnetism relationships.
