Phase diagram of the bcc S=1/2 Heisenberg antiferromagnet with first and second neighbor exchange -: art. no. 064416

We use linked-cluster series expansions, both at T=0 and high temperature, to analyze the phase structure of the spin-1/2 Heisenberg antiferromagnet with competing first- and second-neighbor interactions on the three-dimensional body-centered-cubic lattice. At zero temperature we find a first-order quantum phase transition at J(2)/J(1)similar or equal to0.705+/-0.005 between AF(1) (Neel) and AF(2) ordered phases. The high-temperature series yield quite accurate estimates of the bounding critical line for the AF(1) phase, and an apparent critical line for the AF(2) phase, with a bicritical point at J(1)/J(2)similar or equal to0.71, kT/J(1)similar or equal to0.34. The possibility that this latter transition is of first order cannot be excluded.