58 research outputs found
Noncollinear magnetic order in quasicrystals
Based on Monte-Carlo simulations, the stable magnetization configurations of
an antiferromagnet on a quasiperiodic tiling are derived theoretically. The
exchange coupling is assumed to decrease exponentially with the distance
between magnetic moments. It is demonstrated that the superposition of
geometric frustration with the quasiperiodic ordering leads to a
three-dimensional noncollinear antiferromagnetic spin structure. The structure
can be divided into several ordered interpenetrating magnetic supertilings of
different energy and characteristic wave vector. The number and the symmetry of
subtilings depend on the quasiperiodic ordering of atoms.Comment: RevTeX, 4 pages, 5 low-resolution color figures (due to size
restrictions); to appear in Physical Review Letter
Spin-spin correlations in ferromagnetic nanosystems
Using exact diagonalization, Monte-Carlo, and mean-field techniques,
characteristic temperature scales for ferromagnetic order are discussed for the
Ising and the classical anisotropic Heisenberg model on finite lattices in one
and two dimensions. The interplay between nearest-neighbor exchange, anisotropy
and the presence of surfaces leads, as a function of temperature, to a complex
behavior of the distance-dependent spin-spin correlation function, which is
very different from what is commonly expected. A finite experimental
observation time is considered in addition, which is simulated within the
Monte-Carlo approach by an incomplete statistical average. We find strong
surface effects for small nanoparticles, which cannot be explained within a
simple Landau or mean-field concept and which give rise to characteristic
trends of the spin-correlation function in different temperature regimes.
Unambiguous definitions of crossover temperatures for finite systems and an
effective method to estimate the critical temperature of corresponding infinite
systems are given.Comment: 7 pages, 5 figures, EPJB (in press
Magnetic properties of single atoms of Fe and Co on Ir(111) and Pt(111)
In using the fully relativistic versions of the Embedded Cluster and Screened
Korringa-Kohn-Rostoker methods for semi-infinite systems the magnetic
properties of single adatoms of Fe and Co on Ir(111) and Pt(111) are studied.
It is found that for Pt(111) Fe and Co adatoms are strongly perpendicularly
oriented, while on Ir(111) the orientation of the magnetization is only
out-of-plane for a Co adatom, for an Fe adatom it is in-plane. For comparison
also the so-called band energy parts of the anisotropy energy of a single layer
of Fe and Co on these two substrates are shown. The obtained results are
compared to recent experimental studies using e.g. the spin-polarized STM
technique
Observation of a Complex Nanoscale Magnetic Structure in a Hexagonal Fe Monolayer
We have observed a novel magnetic structure in the pseudomorphic Fe monolayer on Ir(111). Using spin-polarized scanning tunneling microscopy we find a nanometer-sized two-dimensional magnetic unit cell. A collinear magnetic structure is proposed consisting of 15 Fe atoms per unit cell with 7 magnetic moments pointing in one and 8 moments in the opposite direction. First-principles calculations verify that such an unusual magnetic state is indeed lower in energy than all solutions of the classical Heisenberg model. We demonstrate that the complex magnetic structure is induced by the strong Fe-Ir hybridization
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