Individual skyrmion manipulation by local magnetic field gradients

Magnetic skyrmions are topologically protected spin textures, stabilised in systems with strong Dzyaloshinskii-Moriya interaction (DMI). Several studies have shown that electrical currents can move skyrmions efficiently through spin-orbit torques. While promising for technological applications, current-driven skyrmion motion is intrinsically collective and accompanied by undesired heating effects. Here we demonstrate a new approach to control individual skyrmion positions precisely, which relies on the magnetic interaction between sample and a magnetic force microscopy (MFM) probe. We investigate perpendicularly magnetised X/CoFeB/MgO multilayers, where for X = W or Pt the DMI is sufficiently strong to allow for skyrmion nucleation in an applied field. We show that these skyrmions can be manipulated individually through the local field gradient generated by the scanning MFM probe with an unprecedented level of accuracy. Furthermore, we show that the probe stray field can assist skyrmion nucleation. Our proof-of-concepts results pave the way towards achieving current-free skyrmion control

Terahertz Spin‐to‐Charge Conversion by Interfacial Skew Scattering in Metallic Bilayers

The efficient conversion of spin to charge transport and vice versa is of major relevance for the detection and generation of spin currents in spin‐based electronics. Interfaces of heterostructures are known to have a marked impact on this process. Here, terahertz (THz) emission spectroscopy is used to study ultrafast spin‐to‐charge‐current conversion (S2C) in about 50 prototypical F|N bilayers consisting of a ferromagnetic layer F (e.g., Ni81Fe19, Co, or Fe) and a nonmagnetic layer N with strong (Pt) or weak (Cu and Al) spin‐orbit coupling. Varying the structure of the F/N interface leads to a drastic change in the amplitude and even inversion of the polarity of the THz charge current. Remarkably, when N is a material with small spin Hall angle, a dominant interface contribution to the ultrafast charge current is found. Its magnitude amounts to as much as about 20% of that found in the F|Pt reference sample. Symmetry arguments and first‐principles calculations strongly suggest that the interfacial S2C arises from skew scattering of spin‐polarized electrons at interface imperfections. The results highlight the potential of skew scattering for interfacial S2C and propose a promising route to enhanced S2C by tailored interfaces at all frequencies from DC to terahertz

Impact of electromagnetic fields and heat on spin transport signals in Y3Fe5O12

Exploring new strategies to perform magnon logic is a key requirement for the further development of magnonbased spintronics. in this paper, we realize a three-terminal magnon transport device to study the possibility of manipulating magnonic spin information transfer in a magnetic insulator via localized magnetic fields and heat generation. the device comprises two parallel pt wires as well as a cu center wire that are deposited on the ferrimagnetic insulator y3fe5o12. while the pt wires act as spin current injector and detector, the cu wire is used to create local magnetostatic fields and additional heat, which impact both the magnetic configuration and the magnons within the y3fe5o12 below. we show that these factors can create a nonlocal signal that shows similar features as compared to an electrically induced magnon flow. furthermore, a modulation of the spin transport signal between the pt wires is observed, which can be partly explained by thermally excited spin currents of different polarization. our results indicate a potential way towards the manipulation of nonlocal magnon signals, which could be useful for magnon logic

Magnetoelectric properties of epitaxial Fe3O4 thin films on (011) PMN-PT piezosubstrates

We determine the magnetic and magnetotransport properties of 33 nm thick Fe3O4 films epitaxially deposited by rf-magnetron sputtering on unpoled (011) [PbMg1/3Nb2/3O3](0.68) - [PbTiO3](0.32) (PMN-PT) substrates. The magnetoresistance (MR), as well as the magnetization reversal, strongly depend on the in-plane crystallographic direction of the epitaxial (011) Fe3O4 film and strain. When the magnetic field is applied along [100], the magnetization loops are slanted and the sign of the longitudinal MR changes from positive to negative around the Verwey transition at 125 K on cooling. Along the [01 (1) over bar] direction, the loops are square shaped and the MR is negative above the switching field across the whole temperature range, just increasing in absolute value when cooling from 300 K to 150 K. The value of the MR is found to be strongly affected by poling the PMN-PT substrate, decreasing in the [100] direction and slightly increasing in the [01 (1) over bar] direction upon poling, which results in a strained film

Terahertz spin-to-charge conversion by interfacial skew scattering in metallic bilayers

The efficient conversion of spin to charge transport and vice versa is of major relevance for the detection and generation of spin currents in spin‐based electronics. Interfaces of heterostructures are known to have a marked impact on this process. Here, terahertz (THz) emission spectroscopy is used to study ultrafast spin‐to‐charge‐current conversion (S2C) in about 50 prototypical F|N bilayers consisting of a ferromagnetic layer F (e.g., Ni81Fe19, Co, or Fe) and a nonmagnetic layer N with strong (Pt) or weak (Cu and Al) spin‐orbit coupling. Varying the structure of the F/N interface leads to a drastic change in the amplitude and even inversion of the polarity of the THz charge current. Remarkably, when N is a material with small spin Hall angle, a dominant interface contribution to the ultrafast charge current is found. Its magnitude amounts to as much as about 20% of that found in the F|Pt reference sample. Symmetry arguments and first‐principles calculations strongly suggest that the interfacial S2C arises from skew scattering of spin‐polarized electrons at interface imperfections. The results highlight the potential of skew scattering for interfacial S2C and propose a promising route to enhanced S2C by tailored interfaces at all frequencies from DC to terahertz

Orbital Engineering of Pulsed Laser Deposited Single-layered Manganite Thin Films

Single-layered manganite, La1-xSr1+xMnO4, crystallizes in a tetragonal structure in which (La, Sr)O layers separate MnO6 octahedra along the c axis providing 2D MnO2 sheets. Within this structure, anisotropic electrical resistivity was observed where the in-plane resistivity at room temperature is about three orders of magnitude smaller than the out-of-plane counterpart. In perovskite manganites, La1-xSrxMnO3, doping Sr turns insulating LaMnO3 to metallic La0.5Sr0.5MnO3 due to double exchange interaction. On the contrary, the tetragonal La1-xSr1+xMnO4 remains insulating at higher doping levels of Sr, although the resistivity reduces by about one order of magnitude. Herein, the insulating state of LaSrMnO4 endures via doping with Sr up to x=0.5 and a charge-orbital order state forms where the Mn3+ cations show a preferential orbital occupation of d_(3x^2-r^2 )and d_(3y^2-r^2 ). Many investigations of perovskite manganites have shown that preferential orbital occupation and charge localization i.e. charge order, are interrelated with crystal structure. In this context, the key points are the Mn-O bond length, the cooperative rotation of MnO6 octahedra and the Jahn-Teller distortion. These factors define whether the charge-orbital state is favorable or not. Owing to the layered structure of La1-xSr1+xMnO4, tilting the MnO6 octahedra is restricted (no Mn-O-Mn bond along the c axis). In this thesis two doping levels of x=0.0 and x=0.5 were chosen in which the MnO6 octahedra are tetragonally distorted and non-distorted, respectively. The growth of thin films on different single-crystalline substrates allows us to alter the in- and out-of-plane lattice constants; to change the bond length of Mn with apical and planar oxygen atoms. In such a way, for each specific doping level, Mn3+ cations may show different orbital occupation than the one recognized in the bulk or single crystal. Indeed several studies have manifested preferential d_(3z^2-r^2 )or d_(x^2-y^2 )orbitals for Mn3+ cations in La1-xSrxMnO3 films under in-plane compressive or tensile strains, respectively, although there is no preferential orbital occupation for Mn3+ cations in bulk or single crystal of La1-xSrxMnO3. In this study the thin films of La1-xSr1+xMnO4 (x=0.0, 0.5) were deposited on different substrates in order to generate in-plane tensile and compressive strains. The details of the thin film deposition conditions are given in section ‎2.4. The crystal parameters of the films were investigated carefully using x-ray diffraction techniques presented in sections ‎3.4 and ‎3.5. The stoichiometry of the films and oxidation state of Mn cations were investigated using x-ray photoelectron spectroscopy as shown in sections ‎4.3 and ‎4.4. The orbital occupation of Mn cations was studied by means of linearly polarized x-ray absorption spectroscopy where electron density in the valence shell of Mn cations was probed with respect to the crystallographic direction. In this fashion, the orbital occupation along the in- and out-of-plane directions could be inspected. Our findings show that preferential orbital occupation in layered manganites on one the hand depends on the doping level, while on the other hand they are robust against artificially applied strain. The former is expected since the energy band level is a function of the electron density of Mn cations. However, unlike perovskite manganites, the artificial strain does not affect the orbital occupation. Such differentiation between doping levels and artificial strain can, based on our findings, be addressed only in the thin film of layered manganites, as in the Perovskite family members the strain can be compensated by rotation of MnO6 octahedra, a feature which is absent in layered structures. The details of the linearly polarized x-ray absorption spectroscopy measurements are given in section ‎5