Spin-resolved inverse photoemission of ferromagnetic surfaces

Inverse photoemission (IPE) with spin-polarized electrons provides a way to measure separately the exchange-split majority and minority bands in ferromagnets above the Fermi level. Consequently spin-resolved IPE turns out to be an outstanding technique for obtaining information on surface magnetism: the magnetization of the topmost atomic layer may be investigated by measuring the exchange splitting of electronic states that are localized within the surface layer. Theoretical models of ferromagnetism may be tested by observing the temperature behavior of bands which contribute to the ferromagnetism of the material. The magnetic coupling of an adsorbate to the ferromagnetic substrate may be studied by probing adsorbate-induced bands. Results for the Ni(110) surface serve as an illustration to discuss the status of spin-resolved IPE and its application to the field of surface magnetism.     

Electronic quasiparticle structure of ferromagnetic bcc iron

We investigate the influence of electron correlations on the temperature-dependence of the electronic structure of ferromagnetic bcc iron by use of a manybody evaluation of a generalized model of magnetism. The single-particle part of the model-Hamiltonian is taken from an LDA band structure calculation. The manybody interactions are described by only two parameters, an intraband Coulomb interactionU and an interband exchangeJ. WithU=1.8 eV andJ=0.2 eV the self-consistent model solution yields aT=0 moment of about 2.04 µ_B and a Curie-temperature of 1044K. Details of the magnetic behaviour of Fe can be traced back to a striking temperature variation of the quasiparticle density of states. A novel explanation for the experimentally-observed non-collapsing exchange splitting is demonstrated in terms of the temperature-dependent spectral density for wave-vectors near the -point. Typical differences in the magnetic behaviour of Fe and Ni are worked out.     

Spin-resolved edge states transport in a normal/ferromagnetic/normal topological insulator junction: The role of interface

The spin-resolved edge states transport in a normal/ferromagnetic/normal topological insulator (TI) junction is investigated numerically. It is shown that the transport properties of the hybrid junction strongly depend on the interface shape. For the junction with two sharp interfaces, a nonzero spin conductance can be generated besides the spin-split energy windows. Moreover, the axial symmetries of the in-plane spin conductance amplitude are broken. The underlying physics is attributed to the sharp-interface-induced quantum interference effect. However, for the hybrid junction with two smooth interfaces, a non-zero spin conductance can only be achieved in the spin-split energy windows. Further, the axial symmetries of the in-plane spin conductance amplitude recover. These findings may not only benefit to further apprehend the spin-dependent edge states transport in the hybrid TI junctions but also provide some theoretical bases to the application of the topological spintronics devices.     

Spin-resolved unoccupied electronic band structure from quantum size oscillations in the reflectivity of slow electrons from ultrathin ferromagnetic crystals

The spin-dependent reflectivity of electrons with energies between 0 and 20 eV from Fe single crystals 2-8 monolayers thick on a W(110) surface is studied by spin-polarized low energy electron microscopy. The quantum size oscillations in the reflectivity are analyzed in a similar manner as in photoemission of ground state electrons, yielding the spin-resolved unoccupied state band structure of Fe in the Gamma N direction in the energy range studied.     

Nuclear spin-lattice relaxation of impurities in ferromagnetic iron

Due to the development of Green's function method the calculation of the nuclear spin-lattice relaxation time of impurities in ferromagnets has become feasible in the last years. We present the result of calculations for allsp andd impurities in ferromagnetic iron. The calculations are based on the density functional formalism. They well, reproduce the experimental trend of the relaxation timeT ₁ for bothsp andd impurities. By decomposing the relaxation rate into various contributions, we explain the observed systematic behavior ofT ₁ T in terms of the local electronic structure.     

Numerical investigation of spin waves in ferromagnetic iron

Spin wave energies and intensities have been calculated along three principal symmetry directions for ferromagnetic iron. These calculations are based on an itinerant model which incorporates band and wave-vector dependence of the relevant Coulomb matrix elements. The results indicate that iron's spin waves can be described completely by an itinerant model without recourse to additional assumptions about strong Hund's rule coupling or local moment behavior.     

Magnetic moments of ferromagnetic and antiferromagnetic bcc and fcc iron

Magnetic moments and total energies of ferromagnetic and antiferromagnetic bcc and fcc iron are obtained as a function of atomic volume by means of self-consistent band-structure calculations using the local spin-density-functional approximation.     

Observations of ferromagnetic correlations at high temperatures in paramagnetic iron

Polarised neutron scattering with polarisation analysis has been used to obtain a unique measurement of the paramagnetic fluctuations in iron at temperatures between 1273 and 1573 K. The results clearly demonstrate almost complete ferromagnetic correlation over distances up to 15 Å. The average moment per atom taking part in the correlation and giving rise to paramagnetic scattering is about 1.3μ_B. These findings should lead to a better understanding of paramagnetism in metals.     

Spin-resolved quantum transport in graphene-based nanojunctions

First-principles calculations were performed to explore the spin-resolved electronic and thermoelectric transport properties of a series of graphene-nanoribbon-based nanojunctions. By flipping the magnetic moments in graphene leads from parallel to antiparallel, very large tunneling magnetoresistance can be obtained under different gate voltages for all the structures. Spin-resolved alternating-current conductance increases versus frequency for the short nanojunctions but decreases for the long nanojunctions. With increasing junction length, the behavior of the junctions changes from capacitive-like to inductive-like. Because of the opposite signs of spin-up thermopower and spin-down thermopower near the Fermi level, pure spin currents can be obtained and large figures of merit can be achieved by adjusting the gate voltage and chemical potential for all the nanojunctions.     

Charge and spin contact density in ferromagnetic iron and nickel

The charge and spin densities of band electrons at a nuclear site are calculated for ferromagnetic iron and nickel. A negative contribution to the hyperfine field is obtained in both cases.     

Partial circular polarization of the spectral thermal emission from ferromagnetic iron

A partial circular polarization of the spectral thermal emission from a single crystal of ferromagnetic iron is observed. The circular polarization changes sign at a wavelength of 1 μm.     

Continuous versus discrete hyperfine-field distributions in amorphous ferromagnetic iron alloys

The Mössbauer spectra of amorphous alloys possess broad absorption lines which are usually attributed to a continuous hyperfine-field distribution. The analysis of such spectra can be made simpler and less ambiguous by eliminating the second and fifth lines (the Δm_I = 0 transitions). By applying a large external magnetic field parallel to the propagation direction of the γ-ray, four-line Mössbauer spectra have been obtained for amorphous Fe₇₈B₁₂Si₁₀ and Fe₄₀Ni₄₀P₁₄B₆ (METGLAS® 2826). A discrete hyperfine-field distribution based on Bernal's liquid-structure model fits the data well. Other aspects of the results are discussed.     

Radiative detection of NMR studies of domain nuclei in enriched ferromagnetic iron

Combined host (∼95 at% enriched stable ⁵⁷Fe) and very dilute impurity (∼0.01 at% radioactive ⁶⁰Co) NMR signals have been obtained on the one sample of polycrystalline Fe foil utilising perturbations to the gamma anisotropy from in situ thermally oriented ⁶⁰Co nuclei for both resonances. The NMR-TDNO signals on the ⁵⁷Fe sites have been followed down to applied magnetic fields well below the host magnetic saturation and exhibited two distinct components; a strong, narrow homogeneous signal, superimposed over a broader inhomogeneous signal. The impurity ⁶⁰Co⁵⁷Fe inhomogeneous resonance has been studied with three pulse NMRON and the irreversible decay of the nuclear spin echo measured as a function of applied magnetic field. This revised version was published online in August 2006 with corrections to the Cover Date.