Phase diagram for a two-dimensional uniaxial dipolar antiferromagnet with an exchange interaction

Abstract Monte Carlo simulation are used to study the magnetic properties of a two dimensional unixial spin system in which the spins are constrained to lie in the plane and couple through a combination of dipolar and nearest neighbour exchange interactions. The phase diagram that results from the variation of the coupling constant J is presented and discussed in relation to the observed ordering of the Er ions in the high Tc superconductor ErBa 2 Cu 3 O 7−δ . An estimate of the value of the coupling constant in ErBa 2 Cu 3 O 7−δ is given.