Antiferromagnetic states in Co_pMg_1−pO (abstract) Available to Purchase

Co_pMg_1−pO offers an excellent prototypical example for the study of antiferromagnetism in diluted fcc lattices. The system retains the same crystallographic structure (NaCl type) over the entire 0≤p≤1 range. The Co²⁺ ions form a randomly diluted fcc spin lattice with predominantly next‐nearest‐neighbor antiferromagnetic (AF) exchange coupling. No significant changes in J are expected with magnetic dilution, since the lattice parameter changes only slightly (∼1%) between p=1 and p=0. The χ(p,T) data¹ for the system reveal a distinct crossover effect at p≊0.45. A similar behavior of the χ(p,T) curve was observed in an isostructural system Eu_pSr_1−pTe, and was interpreted as an AF→SG (SG=spin glass) transition.² Recently, we have reported low‐T neutron‐diffraction data³ from Co_pMg_1−pO samples with various p, showing a breakdown of the type‐II AF long‐range order (LRO) in the system at p≊0.47. In this paper we present the results of measurements of the temperature dependence of magnetic peak intensities and widths which provide a further evidence for a sharp LRO‐SRO (short‐range order) phase boundary in the system. However, neutron‐diffraction data alone cannot answer the question of whether the SRO phase is a SG state. In order to obtain a closer understanding of the LRO‐SRO transition in type‐II antiferromagnets, we have carried out Monte Carlo simulations on diluted fcc spin arrays. Since Co_pMg_1−pO is an Ising‐like system (due to significant crystal‐field anisotropy), and some other materials of current interest (e.g., Eu_pSr_1−pTe) are Heisenberg systems, we discuss this question in context of simulation data obtained from both Heisenberg and Ising spin arrays.