  ThCr2Si2-type phosphide ACo2P2 (A=Rare earth elements) has the same structure
as iron arsenides, but their magnetic behaviors are quite distinct. In this
paper, we for the first time grew a series of La1-xCexCo2P2 single crystals
(x=0.0 to1.0), and made structural and magnetic characterizations. This allows
us to carry out a careful investigation on the evolution of magnetism with
cerium content and build a magnetic phase diagram. We found that the
introduction of cerium induces a rapid decrease of c-axis and a change from
ferromagnetic (FM) to antiferromagnetic (AFM) states. By employing
first-principles band-structure calculations, we identify the formation of P-P
bonding with the shortening of c-axis, which effectively drives an increase of
AFM interaction and eventually leads to AFM ordering in the high doping region.
The present study may shed light on the interplay between the structural
collapsing and electronic/magnetic properties in 122 iron pnictides.
