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We have studied the Heisenberg antiferromagnets characterized by the magneticstructures with the periods being two times larger than the lattice period. Wehave considered all the types of the Bravais lattices (simple cubic, bcc andfcc) and divided all these antiferromagnets into 7 classes i.e. 3 plus 4classes denoted with symbols A and B correspondingly. The order parametercharacterizing the degeneracies of the magnetic structures is an ordinary Neelvector for A classes and so-called 4-complex for B classes. We have taken intoaccount the fluctuation corrections for these states within the spin-wave andlarge-N expansions ($N$ is the number of spin components). Below the Neeltemperature $T_{\rm{N}}$ quantum and thermal fluctuations lift the degeneracymaking simple one-wave vector collinear structure preferable for all theclasses. A satellite of this effect is opening of the exchange gaps at certainwave vectors in the spin wave spectrum (there is an analogous effect for thenonuniform static transverse susceptibility). However, as the temperatureapproaches $T_{\rm{N}}$, the exchange gaps are closing. We have calculated thecritical indices $\eta$ and $\nu$ to order of $1/N$ and found that they differfor A and B classes.

Frustrated Heisenberg Antiferromagnets on Cubic Lattices: Magnetic Structures, Exchange Gaps, and Non-Conventional Critical Behaviour