Mechanisms for anomalous magnetic orderings in Yb monopnictides

Anomalous magnetic orderings in Yb monopnictides YbXp were investigated in detail. Even though the nearest and next nearest-neighbour exchange constants J₁ and J₂ are nearly independent of Xp, various types of orderings are observed. Nonmagnetic order in YbSb is attributed to the pair singlet ground state due to a pair exchange Jahn-Teller. From two different types of orderings in YbN, YbAs and in YbP with reduced ordered moments, J₁ = 2J₂ is obtained and it is shown that the above condition is consistent with the instability of the pair singlet. The relation J₁ = 2J₂ is shown to be consistent with the superexchange mechanisms through the p-f mixing. Differently from GdXp, the ferromagnetic exchange for J₁ through the d-f mixing is weak particularly in the Γ₆ ground state.