Theory of a new type of antiferromagnetism in the ideal fcc system Cu

In Cu the competition between the dipolar and Ruderman-Kittel interaction results in a simple type-I-antiferromagnetic ordering with Q= (2 π/a)(1, 0, 0), which is nearly degenerated with a ΓK ordering with Q = (2π/a)(0, η, η) for 0.6 < η < 1. I is shown that the observed new three sublattice structure with η = 2/3 is indeed stabilized by quantum fluctuation effects.