We have investigated the magnetism of the bare and graphene-covered (111) surface of a Ni single crystal employing three different magnetic imaging techniques and ab initio calculations, covering length scales from the nanometer regime up to several millimeters. With low temperature spinpolarized scanning tunneling microscopy (SP-STM) we find domain walls with widths of 60 -90 nm, which can be moved by small perpendicular magnetic fields. Spin contrast is also achieved on the graphene-covered surface, which means that the electron density in the vacuum above graphene is substantially spin-polarized. In accordance with our ab initio calculations we find an enhanced atomic corrugation with respect to the bare surface, due to the presence of the carbon pz orbitals and as a result of the quenching of Ni surface states. The latter also leads to an inversion of spinpolarization with respect to the pristine surface. Room temperature Kerr microscopy shows a stripe like domain pattern with stripe widths of 3 -6 µm. Applying in-plane-fields, domain walls start to move at about 13 mT and a single domain state is achieved at 140 mT. Via scanning electron microscopy with polarization analysis (SEMPA) a second type of modulation within the stripes is found and identified as 330 nm wide V-lines. Qualitatively, the observed surface domain pattern originates from bulk domains and their quasi-domain branching is driven by stray field reduction.

We probe the spin dynamics in a thin magnetic film at ferromagnetic resonance by nuclear resonant scattering of synchrotron radiation at the 14.4 keV resonance of 57 Fe. The precession of the magnetization leads to an apparent reduction of the magnetic hyperfine field acting at the 57 Fe nuclei. The spin dynamics is described in a stochastic relaxation model adapted to the ferromagnetic resonance theory by Smit and Beljers to model the decay of the excited nuclear state. From the fits of the measured data the shape of the precession cone of the spins is determined. Our results open a new perspective to determine magnetization dynamics in layered structures with very high depth resolution by employing ultrathin isotopic probe layers.

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Based on micromagnetic simulations, we report on a novel magnetic helix in a soft magnetic film that is sandwiched between and exchange-coupled to two hard magnetic layers with different anisotropies. We show that such a confined helix stays stable without the presence of an external magnetic field. The magnetic stability is determined by the energy minimization and is a result of an internal magnetic field created by the exchange interaction. We show that this internal field stores a magnetic energy density of a few kJ/m3. We also find that it dramatically modifies ferromagnetic resonances, such that the helix can be used as a ferromagnetic resonance filter and a fast acting attenuator.

Nuclear resonant x-ray diffraction in grazing incidence geometry is used to determine the lateral magnetic configuration in a one-dimensional lattice of ferromagnetic nanostripes. During magnetic reversal, strong nuclear superstructure diffraction peaks appear in addition to the electronic ones due to an antiferromagnetic order in the nanostripe lattice. We show that the analysis of the angular distribution together with the time dependence of the resonantly diffracted x rays reveals surface spin structures with very high sensitivity. This scattering technique provides unique access to laterally correlated spin configurations in magnetically ordered nanostructures and, in perspective, also to their dynamics. DOI: 10.1103/PhysRevLett.118.237204 Resonant magnetic x-ray scattering of synchrotron radiation [1][2][3] is an established tool to probe magnetism in crystalline systems, ultrathin films, and multilayer structures. It allows us to identify magnetic order as well as the magnitude and orientation of magnetic moments with high elemental specificity. Magnetic long range ordering leads to Bragg diffraction from which valuable structural magnetic information can be extracted. While the width of the Bragg peaks is coupled to the crystal quality or strain of magnetic lattices, their peak position and intensity yield lattice parameters, content of the unit cell, or the arrangement of magnetic moments. Monitoring these diffraction peaks under the influence of external fields, pressure, temperature variation, or growth thus enables a detailed in situ characterization of nanomagnetic systems.During the last few decades, resonant x-ray diffraction and reflectometry were extensively applied to reveal the magnetic structure of various crystalline alloys [4][5][6] and superlattices [7][8][9][10][11][12]. Despite the growing need for the characterization of extended patterned magnetic structures like spin ice [13,14] or Skyrmion thin film systems [15][16][17], only a few resonant magnetic x-ray diffraction studies on such systems were carried out [18][19][20][21]. Most of these studies were performed at the L 3 edges of Fe or Co and deal with the field dependent shape of nanostripe domain patterns [22,23]. Using resonant soft x-ray diffraction, Chesnel et al. studied the field dependent magnetic configuration in a dipolar coupled multilayer grating [24].Here we show that nuclear resonant surface diffraction provides unique insight into the magnetism of patterned nanostructures. Applicable to various alloys containing Mössbauer isotopes, the technique offers a significant number of features not accessible by other techniques. Nuclear diffraction discriminates the resonantly scattered (delayed) x rays from the dominating electronic (prompt) ones via time gating, enabling us to detect a pure magnetic signal with very high signal-to-noise ratio. This yields superior sensitivity to detect magnetic superstructures in low-dimensional systems, weak contributions of magnetic order in a lattice, or the smallest variations of magne...

Robust and energetically efficient magnetic structures that employ the spin degree of freedom to store and process information are at the heart of modern spinbased technology. It has recently been shown that the transmission and processing of information without electric currents or external fields can be achieved via the spin degree of freedom subjected to exchange, Ruderman-Kittel-Kasuya-Yosida (RKKY) or long-range dipolar interactions. When structural boundaries fix the magnetization, these interactions can topologically stabilize configurations like spin helices of required periodicity without any presence of chiral Dzyaloshinskii-Moriya interaction. It has been pointed out theoretically that these topologically stabilized helices can be used for magnetic energy storage if they are produced experimentally at the nanoscale

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