168 research outputs found

    Uncompensated magnetization and exchange-bias field in La0.7_{0.7}Sr0.3_{0.3}MnO3_3/YMnO3_3 bilayers: The influence of the ferromagnetic layer

    Get PDF
    We studied the magnetic behavior of bilayers of multiferroic and nominally antiferromagnetic o-YMnO3_3 (375~nm thick) and ferromagnetic La0.7_{0.7}Sr0.3_{0.3}MnO3_3 and La0.67_{0.67}Ca0.33_{0.33}MnO3_3 (8…225 8 \ldots 225~nm), in particular the vertical magnetization shift MEM_E and exchange bias field HEH_E for different thickness and magnetic dilution of the ferromagnetic layer at different temperatures and cooling fields. We have found very large MEM_E shifts equivalent to up to 100\% of the saturation value of the o-YMO layer alone. The overall behavior indicates that the properties of the ferromagnetic layer contribute substantially to the MEM_E shift and that this does not correlate straightforwardly with the measured exchange bias field HEH_E.Comment: 10 figures, 8 page

    Comment on: "Revealing common artifacts due to ferromagnetic inclusions in highly oriented pyrolytic graphite", by M. Sepioni, R.R. Nair, I.-Ling Tsai, A.K. Geim and I.V. Grigorieva, EPL 97 (2012) 47001

    Full text link
    This comment addresses several issues in the paper by Sepioni et al., where it is stated that the ferromagnetism in pristine highly oriented pyrolytic graphite (HOPG) reported by several groups in the previous years is most likely due to impurity contamination. In this comment, clear arguments are given why this statement is not justified. Furthermore, it is pointed out, that there are already measurements using element-sensitive microscopic techniques, e.g. X-ray Magnetic Circular Dichroism (XMCD) that directly proved the intrinsic origin of the ferromagnetism in graphite, also in pristine HOPG.Comment: 1, 0 figures, 9 reference

    Direct Observation of Large Amplitude Spin Excitations Localized in a Spin-Transfer Nanocontact

    Full text link
    We report the direct observation of large amplitude spin-excitations localized in a spin-transfer nanocontact using scanning transmission x-ray microscopy. Experiments were conducted using a nanocontact to an ultrathin ferromagnetic multilayer with perpendicular magnetic anisotropy. Element resolved x-ray magnetic circular dichroism images show an abrupt onset of spin excitations at a threshold current that are localized beneath the nanocontact, with average spin precession cone angles of 25{\deg} at the contact center. The results strongly suggest that we have observed a localized magnetic soliton.Comment: 5 pages, 3 figure

    The role of hydrogen in room-temperature ferromagnetism at graphite surfaces

    Full text link
    We present a x-ray dichroism study of graphite surfaces that addresses the origin and magnitude of ferromagnetism in metal-free carbon. We find that, in addition to carbon π\pi states, also hydrogen-mediated electronic states exhibit a net spin polarization with significant magnetic remanence at room temperature. The observed magnetism is restricted to the top ≈\approx10 nm of the irradiated sample where the actual magnetization reaches ≃15 \simeq 15 emu/g at room temperature. We prove that the ferromagnetism found in metal-free untreated graphite is intrinsic and has a similar origin as the one found in proton bombarded graphite.Comment: 10 pages, 5 figures, 1 table, submitted to New Journal of Physic

    π\pi-Electron Ferromagnetism in Metal Free Carbon Probed by Soft X-Ray Dichroism

    Full text link
    Elemental carbon represents a fundamental building block of matter and the possibility of ferromagnetic order in carbon attracted widespread attention. However, the origin of magnetic order in such a light element is only poorly understood and has puzzled researchers. We present a spectromicroscopy study at room temperature of proton irradiated metal free carbon using the elemental and chemical specificity of x-ray magnetic circular dichroism (XMCD). We demonstrate that the magnetic order in the investigated system originates only from the carbon π\pi-electron system.Comment: 10 pages 3 color figure

    X-Ray Detection of Transient Magnetic Moments Induced by a Spin Current in Cu

    Full text link
    We have used a MHz lock-in x-ray spectro-microscopy technique to directly detect changes of magnetic moments in Cu due to spin injection from an adjacent Co layer. The elemental and chemical specificity of x-rays allows us to distinguish two spin current induced effects. We detect the creation of transient magnetic moments of 3×10−53\times 10^{-5} μB\mu_\mathrm{B} on Cu atoms within the bulk of the 28 nm thick Cu film due to spin-accumulation. The moment value is compared to predictions by Mott's two current model. We also observe that the hybridization induced existing magnetic moments on Cu interface atoms are transiently increased by about 10% or 4×10−34\times 10^{-3} μB\mu_\mathrm{B}. This reveals the dominance of spin-torque alignment over Joule heat induced disorder of the interfacial Cu moments during current flow

    Magnetic versus crystal field linear dichroism in NiO thin films

    Full text link
    We have detected strong dichroism in the Ni L2,3L_{2,3} x-ray absorption spectra of monolayer NiO films. The dichroic signal appears to be very similar to the magnetic linear dichroism observed for thicker antiferromagnetic NiO films. A detailed experimental and theoretical analysis reveals, however, that the dichroism is caused by crystal field effects in the monolayer films, which is a non trivial effect because the high spin Ni 3d83d^{8} ground state is not split by low symmetry crystal fields. We present a practical experimental method for identifying the independent magnetic and crystal field contributions to the linear dichroic signal in spectra of NiO films with arbitrary thicknesses and lattice strains. Our findings are also directly relevant for high spin 3d53d^{5} and 3d33d^{3} systems such as LaFeO3_{3}, Fe2_{2}O3_{3}, VO, LaCrO3_{3}, Cr2_{2}O3_{3}, and Mn4+^{4+} manganate thin films

    Revealing common artifacts due to ferromagnetic inclusions in highly-oriented pyrolytic graphite

    Full text link
    We report on an extensive investigation to figure out the origin of room-temperature ferromagnetism that is commonly observed by SQUID magnetometry in highly-oriented pyrolytic graphite (HOPG). Electron backscattering and X-ray microanalysis revealed the presence of micron-size magnetic clusters (predominantly Fe) that are rare and would be difficult to detect without careful search in a scanning electron microscope in the backscattering mode. The clusters pin to crystal boundaries and their quantities match the amplitude of typical ferromagnetic signals. No ferromagnetic response is detected in samples where we could not find such magnetic inclusions. Our experiments show that the frequently reported ferromagnetism in pristine HOPG is most likely to originate from contamination with Fe-rich inclusions introduced presumably during crystal growth.Comment: 8 pages, 7 figure

    Direct observation and imaging of a spin-wave soliton with p−p-like symmetry

    Get PDF
    The prediction and realization of magnetic excitations driven by electrical currents via the spin transfer torque effect, enables novel magnetic nano-devices where spin-waves can be used to process and store information. The functional control of such devices relies on understanding the properties of non-linear spin-wave excitations. It has been demonstrated that spin waves can show both an itinerant character, but also appear as localized solitons. So far, it was assumed that localized solitons have essentially cylindrical, s−s-like symmetry. Using a newly developed high-sensitivity time-resolved magnetic x-ray microscopy, we instead observe the emergence of a novel localized soliton excitation with a nodal line, i.e. with p−p-like symmetry. Micromagnetic simulations identify the physical mechanism that controls the transition from s−s- to p−p-like solitons. Our results suggest a potential new pathway to design artificial atoms with tunable dynamical states using nanoscale magnetic devices
    • …
    corecore