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Polarized neutron scattering experiments on the slightly overdoped superconductor Ba0.5K0.5Fe2As2 reveal broad magnetic resonance scattering peaking at approximately 15 meV. In spite of doping far beyond the suppression of magnetic order, this compound exhibits dispersive and anisotropic magnetic excitations. At energies below the resonance maximum, magnetic correlations polarized parallel to the layers but perpendicular to the propagation vector are reduced by a factor of 2 compared to those in the two orthogonal directions; in contrast, correlations at the peak maximum are isotropic. [ABSTRACT FROM AUTHOR]

A magnetoresistance method is proposed which extracts both the growth direction mobility and the planar mobility of an anisotropic thin film, such as a superlattice. A magnetic field which varies in magnitude and orientation is employed. Errors appearing in previous magnetotransport studies on superlattices are resolved. In particular, it is shown that the contact layers used to send currents through an active region do not have a negligible resistance, even if they are much more conductive than the active region. The technique is demonstrated on an InAs/GaSb-based structure where the growth axis to planar mobility anisotropy ratio is found to drop rapidly with increasing temperature. [ABSTRACT FROM AUTHOR]

We investigated the electronic structure of Na2IrO3 using optical spectroscopy, first-principles calculation, and x-ray absorption spectroscopy. We found that the electronic structure of Na2IrO3 is mainly determined by anisotropic hopping interactions and spin-orbit coupling. Due to the hopping interaction, the orbital character of the bands near the Fermi level deviates from the spin-orbit coupling-induced Jeff = 1/2 states. Polarization-dependent O 1s x-ray absorption spectroscopy showed that the Jeff = 1/2 state of an Ir atom can be mixed with the Jeff = 3/2 state of the neighboring Ir atom. This result implies that mixing between the Jeff = 1/2 and 3/2 states in the valence state should be carefully considered in proposed exotic states of Na2IrO3, such as topological insulator and quantum spin liquid states. [ABSTRACT FROM AUTHOR]

The π-plasmon dispersion in graphene was scrutinized by momentum-resolved electron energy-loss spectroscopy with an improved momentum q resolution and was found to display the square root of the q dispersion characteristic of the collective excitation of two-dimensional electron systems, in contrast to previous experimental and theoretical studies which reported a linear q dispersion. Our theoretical elaborations on the q-dependent spectra affirm this square root of q relation and further unveil an in-plane electronic anisotropy. The physical property of the π plasmon is thoroughly compared to that of the two-dimensional plasmon due to carriers of the Dirac fermions. A clear distinction between the π plasmon and the two-dimensional Dirac plasmon is demonstrated, clarifying the common notion about correlating the linearly dispersed Dirac cones with the linear dispersion of the n plasmon previously reported. [ABSTRACT FROM AUTHOR]

The Si(111)-(3 × 1 )Li and Ag surface structures consist of Si honeycomb chains separated by channels occupied by Li or Ag atoms. The dimerization of neighboring Ag atoms results in a larger c(12 × 2)Ag superstructure. We report calculations of the electronic surface states, dielectric function, and reflectance anisotropy spectrum of these surfaces using hybrid density functional theory (DFT) methods. The positions of surface states and the reflectance anisotropy spectrum calculated using DFT are in very good agreement with experimental results, where they have been reported. The surface states which contribute to the reflectance anisotropy below the band gap are identified for each orientation of the incident electromagnetic field. [ABSTRACT FROM AUTHOR]

The overall and element specific magnetism in an exchange biased [Ni80Fe20/Mn]3 film system, with film layers 3.5 nm thick, has been studied to examine the magnetism between interfacial Mn, Ni, and Fe spins. Field-cooling the film results in large exchange bias loop shifts at temperatures from 2 to 30 K, and an enhanced coercivity remains until 75 K. The elemental magnetism ascertained from x-ray magnetic circular dichroism measurements shows that Mn appears to be a fully compensated antiferromagnet down to 20 K, and there is clear evidence of an enhanced orbital moment for both Fe and Ni from 20 to 300 K. This magnetism is likely due to overlapping d orbitals between Fe-Mn and Ni-Mn, with this coupling increasing the local anisotropy resulting in the enhanced coercivity and enabling exchange bias. [ABSTRACT FROM AUTHOR]

The anisotropic upper critical field, Hc2(T), curves for K0.8Fe1.76Se2 are determined over a wide range of temperatures down to 1.5 K and magnetic fields up to 60 T. Anisotropic initial slopes of Hc2 ∼ -1.4 T/K and -4.6 T/K for magnetic field applied along c axis and ab plane, respectively, were observed. Whereas the c axis Hc2c (T) increases quasilinearly with decreasing temperature, the ab plane Hc2ab(T) shows a flattening, starting near 25 K above 30 T. This leads to a nonmonotonic temperature dependence of the anisotropy parameter γH≡ Hc2ab/Hc2c. The anisotropy parameter is ∼2 near Tc∼32 K and rises to a maximum γH∼ 3.6 around 27 K. For lower temperatures, γH decreases with T in a linear fashion, dropping to γH∼2.5 by T∼18 K. Despite the apparent differences between the K0.8Fe1.76Se2 and (Ba0.55K0.45)Fe2As2 or Ba(Fe0.926Co0.074)2As2, in terms of the magnetic state and proximity to an insulating state, the Hc2(T) curves are remarkably similar. [ABSTRACT FROM AUTHOR]

We report detailed Knight-shift measurements of the two indium sites in the heavy-fermion compound CeIrIn5 as a function of temperature and field orientation. We find that the Knight-shift anomaly is orientation dependent, with a crossover temperature T* that varies by 50% as the field is rotated from (001) to (100). This result suggests that the hybridization between the Ce 4f states and the itinerant conduction electrons is anisotropic, a result that reflects its collective origin, and may lead to anisotropic Kondo liquid behavior and unconventional superconductivity. [ABSTRACT FROM AUTHOR]

We report measurements of the anisotropic upper critical field Hc2(T) for K2Cr3As3 single crystals up to 60 T and T>0.6K. Our results show that the upper critical field parallel to the Cr chains, H⊥c2(T), exhibits a paramagnetically limited behavior, whereas the shape of the H⊥c2(T) curve (perpendicular to the Cr chains) has no evidence of paramagnetic effects. As a result, the curves H⊥c2(T) and H‖c2(T) cross at T≈4K, so that the anisotropy parameter γH(T)=H⊥c2/H⊥c2(T) increases from γH(Tc)≈0.35 near Tc to γH(0)≈1.7 at 0.6 K. The paramagnetically limited behavior of H⊥c2(T) is inconsistent with triplet superconductivity but suggests a form of singlet superconductivity with the electron spins locked onto the direction of Cr chains. [ABSTRACT FROM AUTHOR]

We have investigated the superconducting (SC)-gap anisotropy for several Ba-doped KFe2As2 samples using laser-based angle-resolved photoemission spectroscopy. We show that the SC-gap anisotropy and node positions drastically change with a small amount of Ba doping. Our results totally exclude a possibility of d-wave symmetry and strongly suggest that both spin and orbital fluctuations are important for the pairing interaction in the Ba-doped K122. [ABSTRACT FROM AUTHOR]

The large spread of published values for spin Hall angles, even for the most studied normal-metal platinum, reflects the difficulty of investigating the inverse spin Hall effect. In this Rapid Communication we examine the inverse spin Hall effect and anisotropic magnetoresistance for different Ni81Fe19(Py)/normal-metal bilayers operated by spin pumping using a coplanar waveguide. Angle, frequency, and temperature dependent measurements show that spin pumping and the inverse spin Hall effect can be used to quantify spin Hall angles only when the anisotropic magnetoresistance as a parasitic voltage generating effect is avoided. In this case we obtain spin Hall angles of 0.12 and 0.011 for Pt and Au, respectively. Furthermore, these measurements can be used to determine the spin diffusion length of Pt as a function of temperature. [ABSTRACT FROM AUTHOR]

Dynamic magnetization reversal in the mesofrequency range is studied by ac magneto-optical Kerr effect (ac-MOKE) and ac anisotropic magnetoresistance (ac-AMR) magnetometry in a series of epitaxial and polycrystalline thin magnetic films. The dynamic coercive field was found to scale as a power law with scaling exponents ≤1/2 depending on the ferromagnetic material. In addition, there is a low sweep rate regime in which the dynamic coercivity reaches a minimum. These findings are explained in the context of reversal proceeding by motion of a few domain walls (~1). At dc and low field sweep rates the reversal proceeds between local pinning sites via Barkhausen avalanches and the overall reversal speed is strongly dependent on the field sweep rate. At higher field sweep rates a continuous motion regime is entered in which the reversal velocity depends linearly on the applied field sweep rate and only an average pinning force is experienced by the wall. The fit of the dynamic coercivity vs applied field sweep rate allows the determination of the average nonlocal pinning field. The nonuniversal scaling exponent can be explained using recently developed models and introducing a field rate-dependent number of active domain walls. [ABSTRACT FROM AUTHOR]

The spin-torque switching of metallic nanopillar spin valves showing strong perpendicular anisotropy are studied. The magnetic states of the layers depend on extrinsic parameters such as the magnetic field and the dc current applied to the device. A state diagram presents a comprehensive graph of the role of those parameters on the spin-valve magnetic response. After explaining how state diagrams can be built and the different possible representation, experimental state diagrams are studied for perpendicular devices and the influence of lateral size, temperature, and field orientation are shown. An analytical model of a purely uniaxial system is presented. It is shown that this simple model does not properly reflect the experimental results, whereas if the symmetry is broken a qualitative agreement is obtained. Finally, the possible origins of the symmetry break are discussed in light of an analytical model and numerical simulations. [ABSTRACT FROM AUTHOR]

The transition between Kondo and Coulomb blockade effects in discontinuous double magnetic tunnel junctions is explored as a function of the size of the CoPt magnetic clusters embedded between AlOx mnnel barriers. A gradual competition between cotunneling enhancement of the tunneling magnetoresistance (TMR) and the TMR suppression due to the Kondo effect has been found in these junctions, with both effects having been found to coexist even in the same sample. It is possible to tune between these two states with temperature (at a temperature far below the cluster blocking temperature). In addition, when further decreasing the size of the CoPt clusters, another gradual transition between the Kondo effect and direct tunneling between the electrodes takes place. This second transition shows that the spin-flip processes found in junctions with impurities in the barrier are in fact due to the Kondo effect. A simple theoretical model able to account for these experimental results is proposed. [ABSTRACT FROM AUTHOR]

The magnetization reversal process within the first two iron layers at the Fe/GaAs(001) interface is found to be different and independent from the Fe thin film bulk as measured by magnetic second-harmonic generation and magneto-optical Kerr effect. The interface magnetization is largely noncollinear from the bulk with an abrupt magnetic boundary and an anisotropic exchange coupling stiffness, weak interlayer coupling but relatively strong intralayer stiffness. In contrast, Fe/GaAs(l 10) exhibits a rigid coupling between interface and bulk magnetization suggesting that the interfacial bonding structure can dramatically change the nature of the exchange coupling. Moreover, the uniaxial magnetic anisotropy in Fe/GaAs(001) extends from the interface to the first 5 nm in the Fe film and is induced by stress. These results are also relevant to other magnetic/nonmagnetic interfaces with abrupt chemical bond structures. [ABSTRACT FROM AUTHOR]

The upper critical fields Hc2(T) of single crystals of Sr1-xEux(Fe0.89Co0.11)2As2 (x -- 0.20 and 0.46) were determined by radio-frequency penetration depth measurements in pulsed magnetic fields. Hc2(T) approaches the Pauli limiting field but shows an upward curvature with an enhancement from the orbital limited field, as inferred from the Werthamer-Helfand-Hohenberg theory. We discuss the temperature dependence of the upper critical fields and the decreasing anisotropy using a two-band BCS model [ABSTRACT FROM AUTHOR]

The magnetocrystalline anisotropy (MCA) of (Ga,Mn)As films has been studied on the basis of ab initio electronic structure theory by performing magnetic torque calculations. An appreciable contribution to the in-plane uniaxial anisotropy can be attributed to an extended region adjacent to the surface. Calculations of the exchange tensor allow to ascribe a significant part to the MCA to the exchange anisotropy, caused either by a tetragonal distortion of the lattice or by the presence of the surface or interface. [ABSTRACT FROM AUTHOR]

We investigated the transport properties of BaFe2As2 single crystals before and after annealing with BaAs powder. The annealing remarkably improves transport properties, in particular, the magnitude of residual resistivity, which decreases by a factor of more than 10. From the resistivity measurement on detwinned crystals, we found that the anisotropy of the in-plane resistivity is remarkably diminished after annealing, indicative of dominant contributions to the charge transport from the carriers with isotropic and high mobility below magnetostructural transition temperature Ts and the absence of nematic state above Ts. We found that the Hall resistivity shows strong nonlinearity against magnetic field, and the magnetoresistance becomes very large at low temperatures. These results give evidence for the manifestation of multiple carriers with distinct characters in the ordered phase below Ts. By analyzing the magnetic-field dependences, we found that at least three carriers equally contribute to the charge transport in the ordered phase, which is in good agreement with the results of recent quantum oscillation measurements. [ABSTRACT FROM AUTHOR]

Describing the origin of uniaxial magnetic anisotropy (UMA) is generally problematic in systems other than single crystals. We demonstrate an in-plane UMA in amorphous CoFeB films on GaAs(001) which has the expected symmetry of the interface anisotropy in ferromagnetic films on GaAs(001), but strength which is independent of, rather than in inverse proportion to, the film thickness. We show that this volume UMA is consistent with a bond-orientational anisotropy, which propagates the interface-induced UMA through the thickness of the amorphous film. It is explained how, in general, this mechanism may describe the origin of in-plane UMAs in amorphous ferromagnetic films. [ABSTRACT FROM AUTHOR]

Standing spin waves in a thin film are used as sensitive probes of interface pinning induced by an antiferromagnet through exchange anisotropy. Using coplanar waveguide ferromagnetic resonance, pinning of the lowest energy spin-wave thickness mode in Ni80Fe20/Ir25Mn75 exchange-biased bilayers was studied for a range of Ir25Mn75 thicknesses. We show that pinning of the standing mode can be used to amplify, relative to the fundamental resonance, frequency shifts associated with exchange bias. The shifts provide a unique "fingerprint" of the exchange bias and can be interpreted in terms of an effective ferromagnetic film thickness and ferromagnet-antiferromagnet interface anisotropy. Thermal effects are studied for ultrathin antiferromagnetic Ir25Mn75 thicknesses, and the onset of bias is correlated with changes in the pinning fields. The pinning strength magnitude is found to grow with cooling of the sample, while the effective ferromagnetic film thickness simultaneously decreases. These results suggest that exchange bias involves some deformation of magnetic order in the interface region. [ABSTRACT FROM AUTHOR]

We present low temperature, magnetotransport measurements on a quasi-two-dimensional electron gas created by Ar+-irradiation of SrTiO3. We observe negative (positive) magnetoresistance for fields applied in (out of) the plane of the electron gas. By modulating the mobility μ of the electron gas through an electrostatic field, we find the in-plane magnetoresistance is a function of the cyclotron frequency. The negative in-plane magnetoresistance can be explained by a drop in boundary scattering, which occurs as the cyclotron orbits become smaller than the finite thickness of the electron gas. These results elucidate the critical role boundary scattering plays in the magnetotransport of quasi-two-dimensional electron gases. The implications of these results on recent magnetotransport measurements of LaAlO3/SrTiO3 samples are discussed. [ABSTRACT FROM AUTHOR]

We have studied the anisotropy in the in-plane resistivity and the electronic structure of isovalent Ru-substituted BaFe2As2 in the antiferromagnetic-orthorhombic phase using well-annealed crystals. The anisotropy in the residual resistivity component increases in proportion to the Ru dopant concentration, as in the case of Co-doped compounds. On the other hand, both the residual resistivity and the resistivity anisotropy induced by isovalent Ru substitution are found to be 1 order of magnitude smaller than those induced by heterovalent Co substitution. Combined with angle-resolved photoemission spectroscopy results, which show almost the same anisotropic band structure for both the parent and the Ru-substituted compounds, we confirm the scenario that the anisotropy in the residual resistivity arises from anisotropic impurity scattering in the magnetostructurally ordered phase rather than directly from the anisotropic band structure of that phase. [ABSTRACT FROM AUTHOR]

A correction to the article "Exchange anisotropy pinning of a standing spin-wave mode," which was published in a 2011 issue is presented.