Magnetism of iron: from the bulk to the monatomic wire

We report on a theoretical study of the lifetime of the first excited state of spin chains made of an odd number of Fe atoms on Cu 2 N/Cu(100). Yan et al (Nat. Nanotech. 10, 40 (2015)) recently observed very long lifetimes in the case of Fe 3 chains. We consider the decay of the first excited state induced by electron-hole pair creation in the substrate. For a finite magnetic field, the two lowest-lying states in the chain have a quasi-Néel state structure.Decay from one state to the other strongly depends on the degree of entanglement of the local spins in the chain. The entanglement in the chain accounts for the long lifetimes that increase exponentially with chain length. Despite their apparently very different properties, the behaviour of odd and even chains is governed by the same kind of phenomena, in particular entanglement effects. The present results account quite well for the lifetimes recently measured by Yan et al on Fe 3

Section: Concluding Summarymentioning

confidence: 99%

Extremely long-lived magnetic excitations in supported Fe chains

Gauyacq

Lorente

2016

“…To investigate the Dzyaloshinskii-Moriya interaction (DMI) magnetism is incorporated within the Stoner model, 46,47 extended to the description of non-collinear magnetic systems: 48,49 …”

Section: Fig 7: (Color Online)mentioning

confidence: 99%

Dzyaloshinskii-Moriya interaction and chiral magnetism in3d−5dzigzag chains: Tight-binding model andab initiocalculations

Kashid

Schena

Zimmermann³

et al. 2014

We investigate the chiral magnetic order in free-standing planar 3d-5d bi-atomic metallic chains (3d: Fe, Co; 5d: Ir, Pt, Au) using first-principles calculations based on density functional theory. We found that the antisymmetric exchange interaction, commonly known as Dzyaloshinskii-Moriya interaction (DMI), contributes significantly to the energetics of the magnetic structure. For the Fe-Pt and Co-Pt chains, the DMI can compete with the isotropic Heisenberg-type exchange interaction and the magneto-crystalline anisotropy energy (MAE), and for both cases a homogeneous left-rotating cycloidal chiral spin-spiral with a wave length of 51Å and 36Å, respectively, were found. The sign of the DMI, that determines the handedness of the magnetic structure changes in the sequence of the 5d atoms Ir(+), Pt(−), Au(+). We used the full-potential linearized augmented plane wave method and performed self-consistent calculations of homogeneous spin spirals, calculating the DMI by treating the effect of spin-orbit interaction (SOI) in the basis of the spin-spiral states in first-order perturbation theory. To gain insight into the DMI results of our ab initio calculations, we develop a minimal tight-binding model of three atoms and 4 orbitals that contains all essential features: the spin-canting between the magnetic 3d atoms, the spin-orbit interaction at the 5d atoms, and the structure inversion asymmetry facilitated by the triangular geometry. We found that spin-canting can lead to spin-orbit active eigenstates that split in energy due to the spin-orbit interaction at the 5d atom. We show that, the sign and strength of the hybridization, the bonding or antibonding character between d-orbitals of the magnetic and non-magnetic sites, the bandwidth and the energy difference between states occupied and unoccupied states of different spin projection determine the sign and strength of the DMI. The key features observed in the trimer model are also found in the first-principles results.

“…Furthermore, it acts to reduce the magnitude of superparamagnetic fluctuation in nanostructures, and hence is a key factor that would determine whether the nanowires have potential applications in, e.g., high-density recording and magnetic memory devices. Ab initio calculations of the MAE have been performed for mainly the Fe and Co linear chains 10,[28][29][30] , while semiempirical tight-binding calculations have been reported for both linear chains and two-leg ladders of Fe and Co [30][31][32] . Very recently, we have carried out systematic ab initio calculations of both the MAE and also the magnetic dipolar (shape) anisotropy energy for all 3d transition metals in both the linear and zigzag structures.…”

Section: Introductionmentioning

confidence: 99%

Magnetic moment and magnetic anisotropy of linear and zigzag4dand5dtransition metal nanowires: First-principles calculations

Tung

Guo

2010

An extensive ab initio study of the physical properties of both linear and zigzag atomic chains of all 4d and 5d transition metals (TM) within the generalized gradient approximation by using the accurate projector-augmented wave method, has been carried out. The atomic structures of equilibrium and metastable states were theoretically determined. All the TM linear chains are found to be unstable against the corresponding zigzag structures. All the TM chains, except Nb, Ag and La, have a stable (or metastable) magnetic state in either the linear or zigzag or both structures. Magnetic states appear also in the sufficiently stretched Nb and La linear chains and in the largely compressed Y and La chains. The spin magnetic moments in the Mo, Tc, Ru, Rh, W, Re chains could be large (≥1.0 µB/atom). Structural transformation from the linear to zigzag chains could suppress the magnetism already in the linear chain, induce the magnetism in the zigzag structure, and also cause a change of the magnetic state (ferromagnetic to antiferroamgetic or vice verse). The calculations including the spin-orbit coupling reveal that the orbital moments in the Zr, Tc, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Ir and Pt chains could be rather large (≥0.1 µB/atom). Importantly, large magnetic anisotropy energy (≥1.0 meV/atom) is found in most of the magnetic TM chains, suggesting that these nanowires could have fascinating applications in ultrahigh density magnetic memories and hard disks. In particular, giant magnetic anisotropy energy (≥10.0 meV/atom) could appear in the Ru, Re, Rh, and Ir chains. Furthermore, the magnetic anisotropy energy in several elongated linear chains could be as large as 40.0 meV/atom. A spin-reorientation transition occurs in the Ru, Ir, Ta, Zr, La and Zr, Ru, La, Ta and Ir linear chains when they are elongated. Remarkably, all the 5d as well as Tc and Pd chains show the colossal magnetic anisotropy (i.e., it is impossible to rotate magnetization into certain directions). Finally, the electronic band structure and density of states of the nanowires have also been calculated in order to understand the electronic origin of the large magnetic anisotropy and orbital magnetic moment as well as to estimate the conduction electron spin polarization.