Antiferromagnetic orders in Ising model simulations in an icosahedral Zn-Mg-Ho structure

Antiferromagnetic orders were investigated in an icosahedral Zn-Mg-Ho model structure in simulated annealing of 12524 and 67896 Ising spins interacting via a Ruderman-Kittel-Kasuya-Yosida (RKKY)-like alternating exchange. Magnetic orders were analyzed by means of diffraction patterns arising from spin-dependent elastic scattering amplitudes. The diffraction patterns from the magnetic structure consisted of spots at low temperatures in the case of an antiferromagnetic interaction for the shortest distance (3.37 Angstrom) and a ferromagnetic interaction for the second shortest one (5.46 Angstrom). A reversed sign interaction, ferromagnetic for the shortest distance and antiferromagnetic for the second shortest one, resulted in broad intensity minima. The characteristics were clearer in the larger system consisting of 67896 spins. The broad feature in the patterns for the reversed sign interactions was concluded to result from the frustrated second shortest interactions on the basis of an energetic view of the neighboring magnetic connections. (C) 2000 Elsevier Science B.V. All rights reserved.