Volume 91, Issue 10, 15 May 2002
Index of content:
- QUANTUM DOTS, NANO-WIRES, AND LAYERS
91(2002); http://dx.doi.org/10.1063/1.1452701View Description Hide Description
We studied magnetic properties of regular arrays of magnetic dots on a magnetic layer. We took into account the exchange interaction, the dipolar interaction of amplitude D between spins, and the perpendicular anisotropyA. The spins are of the classical Heisenberg model. Due to the competition between D and A, the ground state (GS) can be perpendicular or parallel to the substrate. We have studied the body-centered-cubic and hexagonal-close-packed dot lattices. We have determined the GS magnetic structure as a function of A and D by a steepest descent method. The results show that below (above) a critical value of the GS spin configuration is perpendicular (parallel). We have studied finite-temperature properties of our system of dots in the vicinity of the critical by Monte Carlo simulations. The obtained results show spectacular features, in particular on the spin reorientation. A phase diagram in the vinicity of the critical value of is presented.
91(2002); http://dx.doi.org/10.1063/1.1450762View Description Hide Description
We present experimental studies of the magnetization of electrons in semiconductorquantum dots. Starting from a modulation-doped AlGaAs/GaAs heterostructure an array of dots was patterned by laser-interference lithography and deep mesa etching. The quantum-dot array was integrated into a highly sensitive micromechanical cantilever magnetometer. At a temperature of 0.3 K we observe pronounced oscillations in the magnetization. With regard to their periodicity and temperature dependence they differ from the de Haas–van Alphen effect observed in a two-dimensional electron system. We find that the magnetization calculated from the single-particle Fock–Darwin energies of a quantum dot does not reproduce the experiment. From this we conclude that the electronic ground state of the dots is strongly influenced by electron–electron interaction.
91(2002); http://dx.doi.org/10.1063/1.1458923View Description Hide Description
We investigate the magnetic ground states of iron inclusions embedded in fcc copper using first principles calculations. Of main interest are linear monatomic chains of atoms aligned along different directions in a Cu matrix. The method of calculation we employ is the locally selfconsistent multiple scattering (LSMS) real space method for solving the LDA Kohn–Sham–Dirac equation. We have extended our code to perform fully relativistic calculations to enable us to investigate the spin–orbit coupling effects leading to anisotropic and potentially noncollinear ordering of magnetic moments in these systems of iron inclusions in copper. With this approach we find that the magnetocrystallineanisotropy in systems of magnetic iron chains embedded in copper strongly prefers an orientation of the magnetic iron moments perpendicular to the direction of the chain. This competes with the magnetostatic energy of the chains, which is lowest when the moments are aligned parallel to the chain. Our parameter free calculations suggest that, depending on whether the chains of magnetic atoms are embedded in copper along the 100 or 110 directions, the ground state orientation of the magnetic moments on the iron sites can be either parallel or perpendicular to the chain, due to the balance of these competing effects.
Ultrathin Co films on flat and stepped Cu(111) surfaces: Determination of per atom orbital and spin moments91(2002); http://dx.doi.org/10.1063/1.1450782View Description Hide Description
We have used the x-ray magnetic circular dichroism technique to characterize ultrathin Co filmsdeposited on flat and vicinal Cu(111) single crystal surfaces. All films were prepared and characterized in situ, in ultrahigh vacuum. Similar to other investigators we report a 40% increase of the ratio (orbital to spin moment) of ultrathin Co on both flat and vicinal Cu(111). In addition, an apparently correlated enhancement of both the orbital and spin moments is observed for Co on vicinal Cu(111). This finding is in contrast to what has earlier been reported for a similar system, Co on vicinal Cu(100).