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Register a new userStructural and magnetic properties of FeMn$_x$ ($x=$1...6) chains supported on Cu$_2$N / Cu (100)
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Heterogeneous atomic magnetic chains are built by atom manipulation on a Cu$_2$N/Cu (100) substrate. Their magnetic properties are studied and rationalized by a combined scanning tunneling microscopy (STM) and density functional theory (DFT) work completed by model Hamiltonian studies. The chains are built using Fe and Mn atoms ontop of the Cu atoms along the N rows of the Cu$_2$N surface. Here, we present results for FeMn$_x$ ($x$=1...6) chains emphasizing the evolution of the geometrical, electronic, and magnetic properties with chain size. By fitting our results to a Heisenberg Hamiltonian we have studied the exchange-coupling matrix elements $J$ for different chains. For the shorter chains, $x leq 2$, we have included spin-orbit effects in the DFT calculations, extracting the magnetic anisotropy energy. Our results are also fitted to a simple anisotropic spin Hamiltonian and we have extracted values for the longitudinal-anisotropy $D$ and transversal-anisotropy $E$ constants. These parameters together with the values for $J$ allow us to compute the magnetic excitation energies of the system and to compare them with the experimental data.
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Scanning tunnelling microscopy and density functional theory studies of manganese chains adsorbed on Cu$_2$N/Cu (100) reveal an unsuspected electronic edge state at $sim 1$ eV above the Fermi energy. This Tamm-like state is strongly localised to the last Mn atom of the chain and fully spin polarised. However, no equivalence is found for occupied states, and the electronic structure at $sim -1$ eV is mainly spin unpolarised due to the extended $p$-states of the N atoms that mediate the coupling between the Mn atoms in the chain. Odd-numbered Mn chains present an exponentially decreasing direct coupling with distance between the two edges, leading to a vanishing bonding/anti-bonding splitting of states while even-numbered Mn chains present perfect decoupling of both edges due to the the antiferromagnetic ordering of Mn chains.
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We report on the magnetic properties of Fe and Co adatoms on a Cu$_{2}$N/Cu(100)-$c(2 times 2)$ surface investigated by x-ray magnetic dichroism measurements and density functional theory (DFT) calculations including the local coulomb interaction. We compare these results with properties formerly deduced from STM spin excitation spectroscopy (SES) performed on the individual adatoms. In particular we focus on the values of the local magnetic moments determined by XMCD compared to the expectation values derived from the description of the SES data.The angular dependence of the projected magnetic moments along the magnetic field, as measured by XMCD, can be understood on the basis of the SES Hamiltonian. In agreement with DFT, the XMCD measurements show large orbital contributions to the total magnetic moment for both magnetic adatoms.
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