Phases of anisotropic dipolar antiferromagnets

We study systems of classical magnetic dipoles on simple cubic lattices with dipolar and antiferromagnetic exchange interactions. By analysis and Monte Carlo (MC) simulations, we find how the antiferromagnetic phases vary with uniaxial and fourfold anisotropy constants, C and D, as well as with exchange strength J. We pay special attention to the spin reorientation (SR) phase, and exhibit in detail the nature of its broken symmetries. By mean field theory and by MC, we also obtain the ratio of the higher ordering temperature to the SR transition temperature, and show that it depends mainly on D/C, and rather weakly on J. We find a reverse SR transition.Comment: 10 LaTeX pages, 14 eps figures. Submitted to PRB on 03 October 2005. Accepted on 13 December 200