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Artificial fabrication of a monolayer Kagome material can offer a promising opportunity to explore exceptional quantum states and phenomena in low dimensionality. Here, we have systematically studied a monatomic Ni Kagome lattice grown on Pb(111) by scanning tunneling microscopy/spectroscopy (STM/STS) and density functional theory (DFT). Sawtooth edge structures with distinct heights due to subsurface Ni atoms have been revealed, leading to asymmetric edge scattering of surface electrons on Pb(111). In addition, a local maximum at about −0.2 eV in tunneling spectra represents a manifestation of characteristic phase-destructive flat bands. Although charge transfer from underlying Pb(111) substrate results in a vanishing magnetic moment of Ni atoms, the proximity-induced superconducting gap is slightly enhanced on the Ni Kagome lattice. In light of single-atomic-layer Ni Kagome lattice on superconducting Pb(111) substrate, it could serve as an ideal platform to investigate the interplay between Kagome physics and superconductivity down to the two-dimensional limit.

A proximity effect facilitates the penetration of Cooper pairs that permits superconductivity in a normal metal, offering a promising approach to turn heterogeneous materials into superconductors and develop exceptional quantum phenomena. Here, we have systematically investigated proximity-induced anisotropic superconductivity in a monolayer Ni-Pb binary alloy by combining scanning tunneling microscopy/spectroscopy (STM/STS) with theoretical calculations. By means of high-temperature growth, the

We have investigated the magnetic Co atoms self-assembled on the ultraflat stanene on Cu(111) substrate by utilizing scanning tunneling microscopy/spectroscopy (STM/STS) in conjunction with density functional theory (DFT). By means of depositing Co onto the stanene/Cu(111) held at 80 K, Co atoms have developed into the monomer, dimer, and trimer structures containing one, two, and three Co atoms respectively. As per atomically resolved topographic images and bias-dependent apparent heights, the atomic structure models based on Sn atoms substituted by Co atoms have been deduced, which are in agreement with both self-consistent DFT calculations and STM simulations. Apart from that, the projected density of states (PDOS) has revealed a minimum at around -0.5 eV from the Co-3d3z2-r2 minority band, which contributes predominately to the peak feature at about -0.3 eV in tunneling conductance (dI/dU) spectra taken at the Co atomic sites. As a result of the exchange splitting between the Co-3d majority and minority bands, there are non-zero magnetic moments, including about 0.60 uB in monomer, 0.56 uB in dimer, and 0.29 uB in trimer of the Co atom assembly on the stanene. Such magnetic Co atom assembly therefore could provide the vital building blocks in stabilizing the local magnetism on the two-dimensional (2D) stanene with non-trivial topological properties.

Two-dimensional (2D) Pb nanoisland has established an ideal platform for studying the quantum size effects on growth mechanism, electronic structures as well as high-temperature superconductivity. Here, we investigate the growth and quantum well electronic states of the 2D Pb nanoislands on Nb-doped SrTiO3(0 0 1) by scanning tunneling microscopy and spectroscopy. In contrast to Pb/Si(1 1 1), Pb/Cu(1 1 1) and Pb/Ag(1 1 1), there is no wetting layer of Pb formed on the Nb-doped SrTiO3(0 0 1) surface, resulting in isolated Pb nanoislands with an apparent height of 4 atomic layers as the building blocks for the island growth. According to the thickness-dependent quantum well states resolved in both occupied and unoccupied energy regions, the constant group velocity vg = 1.804 × 106 m/s and the Fermi wavevector kF = 1.575 A−1, have been extracted from a linear fit of the Pb(1 1 1) band dispersion along the Γ - L direction. In addition, the energy-dependent scattering phase shift φ(E) obtained by means of the phase accumulation model shows a metallic-like scattering interface analogous to Pb/Ag(1 1 1). These spatially decoupled 2D Pb nanoislands thus realize an opportunity to explore the intrinsic quantum confinement phenomena in nanoscale superconductors on the doped titanium-oxide-type substrate.

Spin-split Rashba bands have been exploited to efficiently control the spin degree of freedom of moving electrons, which possesses a great potential in frontier applications of designing spintronic devices and processing spin-based information. Given an intrinsic breaking of inversion symmetry and sizeable spin–orbit interaction, two-dimensional (2D) surface alloys formed by heavy metal elements exhibit a pronounced Rashba-type spin splitting of the surface states. Here, we have revealed the essential role of atomic orbital symmetry in the hexagonally warped Rashba spin-split surface state of the $$\sqrt 3 \times \sqrt 3 R30^0$$ 3 × 3 R 3 0 0 BiCu2 monatomic alloy by scanning tunneling spectroscopy (STS) and density functional theory (DFT). From dI/dU spectra and calculated band structures, three hole-like Rashba-split bands hybridized from distinct orbital symmetries have been identified in the unoccupied energy region. Because of the hexagonally deformed Fermi surface, quasi-particle interference (QPI) mappings have resolved scattering channels opened from interband transitions of px,py (mj = 1/2) band. In contrast to the s,pz-derived band, the hexagonal warping is predominately accompanied by substantial out-of-plane spin polarization Sz up to 24% in the dispersion of px,py (mj = 1/2) band with an in-plane orbital symmetry.

Two different superstructures form when atomic H is incorporated in the Fe monolayer on Ir(111). Depending on the amount of H provided, either a highly ordered p(2x2) hexagonal superstructure or an irregular roughly square structure is created. We present here spin-polarized scanning tunneling microscopy (SP-STM) measurements which reveal that in both cases the magnetic nanoskyrmion lattice state of the pristine Fe monolayer is modified. Our measurements of the magnetic states in these hydrogenated films are in agreement with superpositions of cycloidal spin spirals which follow the pattern and the symmetry dictated by the H superstructures. We thus demonstrate here the possibility to vary the symmetry of a non-collinear magnetic state in an ultrathin film without changing its substrate., 7 pages, 6 figures

Scanning tunneling spectroscopy measurements of Mn phthalocyanine (MnPc) molecules adsorbed on (√3×√3) surface alloys show single inelastic steps at exclusively positive or negative bias strongly depending on the tip position. This is in contrast to conventional molecular excitation thresholds, which are independent of the current direction and therefore always occur at both positive and negative bias. This polarity selectivity is found to coincide with the spatial distribution of occupied and empty orbitals. Because of the interaction with the substrate, charge transfer into the doubly degenerate dπ orbitals of MnPc takes place. The resulting Jahn-Teller effect lifts the degeneracy and leads to an isospin- or pseudospin-flip excitation, the inelastic analogue of an orbital Kondo resonance., Financial support has been granted by MINECO (MAT2015-66888-C3-2-R and MAT2016-78293-C6-6-R) and FEDER funds. M. Bode acknowledges financial support by DFG through SFB 1170 “ToCoTronics” (project C02).

Spin-polarized scanning tunneling microscopy reveals that the spin-spiral period of a two-atomic-layer-thick Fe film on Ir(111) roughly doubles upon covering the system with a monolayer of Pb. The spin spirals have a zigzag shape and are guided by structural dislocation lines. In contrast to the spin spiral in the bare Fe double layer, the magnetic state of the Pb-covered Fe film responds to an external magnetic field: the spin spiral breaks up into segments, reminiscent of the spin-spiral state in the Fe triple layer on Ir(111), where the external magnetic field induces magnetic skyrmions. This demonstrates that the tuning of noncollinear spin textures is not only possible by interface engineering based on transition metals, but also with other metallic adlayers such as Pb with a filled $d$ shell.

This corrects the article DOI: 10.1103/PhysRevLett.116.017201.

We investigate spin-polarized (SP) electronic transport properties and hybrid states of a single manganese phthalocyanine (MnPc) molecule adsorbed on a Co nanoisland, with the SP scanning tunneling microscopy measurements and the first-principles calculations. Our analyses show that the MnPc molecule can pin the Co surface state to the Fermi level, forming hybrid stationary spin resonance states which, with an antiparallel-magnetization tip, give a resonant SP conductance peak. Our calculations further reveal that as the tip approaches the molecule, electronic and magnetic couplings in the junction are tuned as the Zener indirect exchange coupling becomes prominent, which switches the conduction carriers from s to d electrons and leads to the tailored magnetic moments and magnetoresistance.

Spin-polarized scanning tunneling microscopy investigations reveal a significant increase of the magnetic period of spin spirals in three-atomic-layer-thick Fe films on Ir(111), from about 4nm at 8K to about 65nm at room temperature. We attribute this considerable influence of temperature on the magnetic length scale of noncollinear spin states to different exchange interaction coefficients in the different Fe layers. We thus propose a classical spin model which reproduces the experimental observations and in which the crucial feature is the presence of magnetically coupled atomic layers with different interaction strengths. This model might also apply for many other systems, especially magnetic multilayers., Comment: 5 pages, 2 figures

Magnetic skyrmions are localized nanometer-sized spin configurations with particle-like properties, which are envisioned to be used as bits in next-generation information technology. An essential step toward future skyrmion-based applications is to engineer key magnetic parameters for developing and stabilizing individual magnetic skyrmions. Here we demonstrate the tuning of the non-collinear magnetic state of an Fe double layer on an Ir(111) substrate by loading the sample with atomic hydrogen. By using spin-polarized scanning tunneling microscopy, we discover that the hydrogenated system supports the formation of skyrmions in external magnetic fields, while the pristine Fe double layer does not. Based on ab initio calculations, we attribute this effect to the tuning of the Heisenberg exchange and the Dzyaloshinsky–Moriya interactions due to hydrogenation. In addition to interface engineering, hydrogenation of thin magnetic films offers a unique pathway to design and optimize the skyrmionic states in low-dimensional magnetic materials., Stabilization of skyrmions is one of the key issues in skyrmion-based spintronics. Here the authors demonstrate that hydrogenation can induce the formation of skyrmions in iron thin films, which provides an alternative way to tailor skyrmion states in low-dimensional magnetic materials.

An interesting class of interface-driven non-collinear spin structures, i.e., chiral domain walls, cycloidal spin spirals and Neel-type skyrmions, have been observed in ultrathin transition metal films grown on heavy-element substrates making use of spin-polarized scanning tunneling microscopy (SP-STM) [1]. Due to a lack of structural inversion symmetry at interfaces, they exhibit a unique rotational sense as a consequence of interfacial Dzyaloshinskii-Moriya (DM) interactions. In this talk, I will present our results based on the investigations of such chiral spin textures under the influence of strain relief and the effect of local electric fields. While a nanoskyrmion lattice was revealed for Fe monolayers (ML) grown on Ir(111), a cycloidal spin spiral ground state has been resolved on Fe double-layers (DL) by employing SP-STM with vectorial magnetic field. As a result of a large lattice mismatch between the epitaxially grown Fe-DL film and the underlying Ir(111) substrate, local uniaxial strain relief occurs, leading to dislocation line patterns. Interestingly, the wavevector of spin spirals is strictly guided along the dislocation lines, while the spin spiral's wavefront exhibits a zigzag deformation [2]. By further increasing the Fe coverage to triple-layers (TL), the zigzag spin spiral remains the magnetic ground state, but with an enhanced periodicity as compared to that of Fe-DL. A magnetic phase transition from the spin spiral to a skyrmionic state, and finally to a saturated ferromagnetic state occurs for Fe-TL by applying an external magnetic field. STM-induced writing and deleting of individual skyrmions is demonstrated with a pronounced bias-polarity dependence, suggesting the decisive role of the local electric field between STM tip and Fe film for the switching mechanism [3]. [1] K. von Bergmann, A. Kubetzka, O. Pietzsch, and R. Wiesendanger, J. Phys.: Condens. Matter 26, 394002 (2014) [2] P.-J. Hsu, A. Finco, L. Schmidt, A. Kubetzka, K. von Bergmann, and R. Wiesendanger, Phys. Rev. Lett. 116, 017201 (2016) [3] P.-J. Hsu, A. Kubetzka, A. Finco, N. Romming, K. von Bergmann, and R. Wiesendanger, arXiv:16001.02935 (2016)

The large epitaxial stress induced by the misfit between a triple atomic layer Fe film and an Ir(111) substrate is relieved by the formation of a dense dislocation line network. Spin-polarized scanning tunneling microscopy (SP-STM) investigations show that the strain is locally varying within the Fe film and that this variation affects the magnetic state of the system. Two types of dislocation line regions can be distinguished and both exhibit spin spirals with strain-dependent periods (ranging from 3 nm to 10 nm). Using a simple micromagnetic model, we attribute the changes of the period of the spin spirals to variations of the effective exchange coupling in the magnetic film. This assumption is supported by the observed dependence of the saturation magnetic field on the spin spiral period. Moreover, magnetic skyrmions appear in an external magnetic field only in one type of dislocation line area, which we impute to the different pinning properties of the dislocation lines., 7 pages, 6 figures

We present a scanning tunneling microscopy (STM) study of the domain evolution across two first-order phase transitions of stripe modulations in ${\mathrm{IrTe}}_{2}$ that occur at ${T}_{\mathrm{C}}\ensuremath{\approx}275$ K and ${T}_{\mathrm{S}}\ensuremath{\approx}180$ K, respectively. Phase coexistence of the hexagonal $(1\ifmmode\times\else\texttimes\fi{}1)$ structure and the $(5\ifmmode\times\else\texttimes\fi{}1)$ stripe modulation is observed at ${T}_{\mathrm{C}}$, while various $(p\ifmmode\times\else\texttimes\fi{}1)$ modulations ($p=3n+2$ with $2\ensuremath{\le}n\ensuremath{\in}\mathbb{N}$) are observed below ${T}_{\mathrm{S}}$. Using STM atomic resolution, we observe anisotropic propagation of domain boundaries along different directions, indicating significantly different kinetic energy barriers. These results are consistently explained by a theoretical analysis of the energy barrier for domain wall propagation as obtained by density functional theory. Individual switching processes observed by STM indicate that the wide temperature range of the transition from the $(5\ifmmode\times\else\texttimes\fi{}1)$ stripes to the $(6\ifmmode\times\else\texttimes\fi{}1)$-ordered ground state is probably caused by the numerically limited subset of switching processes that are allowed between a given initial and the final state. The observations on ${\mathrm{IrTe}}_{2}$ are discussed in terms of a ``harmless staircase'' with a finite number of first-order transitions between commensurate phases and within a ``dynamical freezing'' scenario.

Controlling magnetism with electric fields is a key challenge to develop future energy-efficient devices, however, the switching between inversion symmetric states, e.g. magnetization up and down as used in current technology, is not straightforward, since the electric field does not break time-reversal symmetry. Here, we demonstrate that local electric fields can be used to reversibly switch between a magnetic skyrmion and the ferromagnetic state. These two states are topologically inequivalent, and we find that the direction of an electric field directly determines the final state. This observation establishes the possibility to combine energy-efficient electric field writing with the recently envisaged skyrmion racetrack-type memories., Comment: 11 pages, 4 figures, 4 supplementary figures

Phase coexistence phenomena have been intensively studied in strongly correlated materials where several ordered states simultaneously occur or compete. Material properties critically depend on external parameters and boundary conditions, where tiny changes result in qualitatively different ground states. However, up to date, phase coexistence phenomena have exclusively been reported for complex compounds composed of multiple elements. Here we show that charge- and magnetically ordered states coexist in double-layer Fe/Rh(001). Scanning tunnelling microscopy and spectroscopy measurements reveal periodic charge-order stripes below a temperature of 130 K. Close to liquid helium temperature, they are superimposed by ferromagnetic domains as observed by spin-polarized scanning tunnelling microscopy. Temperature-dependent measurements reveal a pronounced cross-talk between charge and spin order at the ferromagnetic ordering temperature about 70 K, which is successfully modelled within an effective Ginzburg–Landau ansatz including sixth-order terms. Our results show that subtle balance between structural modifications can lead to competing ordering phenomena., The coexistence of different magnetic and electronic phases often occurs in materials with complex chemical compositions, allowing for the study of competitive, collaborative, or emergent phenomena. Here, the authors demonstrate such behaviour in ultrathin Fe films on a Rh(001) substrate.

We report on the influence of uniaxial strain relief on the spin spiral state in the Fe double layer grown on Ir(111). Scanning tunneling microscopy (STM) measurements reveal areas with reconstruction lines resulting from uniaxial strain relief due to the lattice mismatch of Fe and Ir atoms, as well as pseudomorphic strained areas. Magnetic field-dependent spin-polarized STM measurements of the reconstructed Fe double layer reveal cycloidal spin spirals with a period on the nm scale. Globally, the spin spiral wave fronts are guided along symmetry-equivalent [112̅] crystallographic directions of the fcc(111) substrate. On an atomic scale the spin spiral propagation direction is linked to the [001] direction of the bcc(110)-like Fe, leading to a zigzag shaped wave front. The isotropically strained pseudomorphic areas also exhibit a preferred magnetic periodicity on the nm scale but no long-range order. We find that already for local strain relief with a single set of reconstruction lines a strict guiding of the spin spiral is realized.

We present a detailed investigation of spectroscopic features located at the central metal ion of MnPc (where Pc represents phthalocyanine) on Ag(001) by means of scanning tunneling spectroscopy (STS) and first-principles theory. STS data taken close to the Fermi level reveal an asymmetric feature that cannot be fitted with a single Fano function representing a one-channel Kondo effect. Instead, our data indicate the existence of a second superimposed feature. Two potential physical origins, a second Kondo channel related to the ${d}_{xz/yz}$ orbitals, and a spectral feature of the ${d}_{{z}^{2}}$ orbital itself, are discussed. A systematic experimental and theoretical comparison of MnPc with CoPc and FePc indicates that the second feature observed on MnPc is caused by the ${d}_{{z}^{2}}$ orbital. This conclusion is corroborated by STM-induced dehydrogenation experiments on FePc and MnPc which in both cases result in a gradual shift towards more positive binding energies and a narrowing of the Kondo resonance. Theoretical analysis reveals that the latter is caused by the reduced hybridization between the $d$ orbital and the substrate. Spatially resolved differential conductivity maps taken close to the respective peak positions show that the intensity of both features is highest over the central Mn ion, thereby providing further evidence against a second Kondo channel originating from the ${d}_{xz/yz}$ orbital of the central Mn ion.

The growth and magnetic domain structure of ultrathin Fe films epitaxially grown on face-centered cubic (fcc) Rh(001) is investigated by spin-polarized scanning tunneling microscopy (SP-STM) at low temperatures $(T=5.5\text{K})$. Our results indicate that the cleaning procedure applied to the Rh(001) substrate plays an important role for the formation of a clean and well-ordered Fe film. The Fe monolayer exhibits an out-of-plane antiferromagnetic $c(2\ifmmode\times\else\texttimes\fi{}2)$ spin structure. Islands of the second Fe layer are found to be out-of-plane ferromagnetic. Coalescence of the double-layer islands results in the formation of larger domains, which extend over several hundred nanometers for a closed two layer film. Further increasing the Fe coverage leads to a reduction of the domain size and the formation of patterns that are reminiscent of stripe domains driven by the competition of surface/interface and shape anisotropy.

We report on a detailed low-energy electron diffraction (LEED) and low-temperature scanning tunneling microscopy (STM) study of the intermetallic surface compound ${\mathrm{CePt}}_{5}$ on Pt(111). Depending on the thickness we observe various diffraction patterns and superstructures. In the low-thickness regime a slightly compressed $(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure is aligned along the $\ensuremath{\langle}1\overline{1}0\ensuremath{\rangle}$ direction of the Pt(111) substrate. STM reveals another, much larger superstructure with a periodicity of ($9.02\ifmmode\pm\else\textpm\fi{}0.45$) nm presumably responsible for the strongly broadened LEED spots. At about 3 unit cells (u.c.) the surface is dominated by a $(3\sqrt{3}\ifmmode\times\else\texttimes\fi{}3\sqrt{3})R{30}^{\ensuremath{\circ}}$ pattern as revealed by LEED satellites and Fourier-transformed high-resolution STM images. It is interpreted as a moir\'e pattern between the film and the substrate. We precisely determine the superstructure of the intermetallic film to $(\frac{10}{9}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\frac{10}{9}\sqrt{3})R{30}^{\ensuremath{\circ}}$ with respect to the Pt(111) substrate. Above 3 u.c. the satellites progressively disappear. A model is developed that consistently describes this thickness-dependent transition. For ${\mathrm{CePt}}_{5}$ films with a thickness between 6 and 11 u.c. the lattice of the compressed $(2\ifmmode\times\else\texttimes\fi{}2)$ superstructure rotates back into the substrate's $\ensuremath{\langle}1\overline{1}0\ensuremath{\rangle}$ directions.

Magnetic organic molecules, such as 3d transition metal phthalocyanines (TMPc), exhibit properties which make them promising candidates for future applications in magnetic data storage or spin-based data processing. Due to their small size, however, TMPc molecules are prone to quantum effects. For example, the interaction of uncompensated molecular spins with conduction electrons of the substrate may lead to the formation of a many-body singlet state, which gives rise to the so-called Kondo effect. Although the Kondo effect of TMPc molecules has been the object of several investigations, a consistent picture to describe under which conditions a Kondo state is formed is still missing. Here, we study the Kondo properties of MnPc on Ag(001) by means of the low-temperature scanning tunneling spectroscopy (LT-STS) measurements. Differential conductance dI/dU spectra reveal a zero-bias peak that is localized on the Mn ion site. Ab initio calculations combined with a many-body treatment of the multiorbital interaction show that the local Hund coupling favors the high-spin configuration on the 3d shell of the central TM atom. Therefore, each orbital gets close to its individual half-filling creating the necessary condition for many of the 3d orbitals to contribute to the observed Kondo resonance. This, however, happens only for the 3dz(2) orbital, whose hybridization to the substrate is much stronger than for the other orbitals thanks to its shape and its orientation.

We report on a detailed quasiparticle interference (QPI) scattering study of the Ni(111) surface by low-temperature scanning tunneling spectroscopy (LT-STS). While conventional constant-separation STS shows two broad features, which are interpreted as the ${\ensuremath{\Lambda}}_{3}$ bulk band and $sp$-like Shockley-type surface state ($sp$-SS), energy-dependent Fourier-transformed QPI maps reveal the band dispersion of the underlying surface electronic features. We find two electronlike branches in the $sp$-SS dispersion, which are interpreted as the exchange-split minority and majority spin part. The exchange splitting is determined to $\ensuremath{\Delta}{E}_{\mathrm{ex}}=100\ifmmode\pm\else\textpm\fi{}8$ meV. In addition, a holelike $d$-derived surface resonance is found. Band onsets and effective electron masses are determined by fitting the band dispersion with a parabola at small $k$ values. Hybridization effects with bulk electronic states are observed towards larger $k$ values. Prominent quantum confinement phenomena of the $sp$-SS are observed in STS data obtained within vacancy islands. The results can be interpreted within a one-dimensional quantum-well model.

We report on the observation of the hysteretic transition of a commensurate charge modulation in IrTe$_2$ from transport and scanning tunneling microscopy (STM) studies. Below the transition ($T_{\rm C} \approx 275$ K on cooling) a $q = 1/5$ charge modulation was observed, which is consistent with previous studies. Additional modulations [$q_n = (3n+2)^{-1}$] appear below a second transition at $T_{\rm S}\approx 180$ K on cooling. The coexistence of various modulations persist up to $T_{\rm C}$ on warming. The atomic structures of charge modulations and the temperature dependent STM studies suggest that 1/5 modulation is a periodic soliton lattice which partially melts below $T_{\rm S}$ on cooling. Our results provide compelling evidence that the ground state of IrTe$_2$ is a commensurate 1/6 charge modulation, which originates from periodic dimerization of Te atoms visualized by atomically resolved STM images., Comment: 5 pages, 5 figures

Spin structures of an exchange-coupled-bilayer system of expanded-face-centered-tetragonal (e-fct) Mn(001) ultrathin films grown on Co/Cu(001) were resolved by means of spin-polarized scanning-tunneling microscopy. With an in-plane spin-sensitive probe, a layered antiferromagnetic-spin ordering of Mn overlayers was evidenced directly. In addition, the spin frustration across the same Mn layer creating a narrow domain wall down to nanometer scale was also observed along the buried step of Co underlayers. According to the micromagnetic simulation, the step-induced domain-wall width is in agreement with the experimental results. Such in-plane layered antiferromagnetic-spin structures of e-fct Mn(001) provide uncompensated spins at the interface with Co underlayers and elucidate the mechanism of the corresponding exchange-bias field observed in the previous studies.

In the field of recording technology, the controllable perpendicular magnetization of magnetic material is of great importance because it's promising for the out-of-plane type of data storage. Generally, the approaches to establish perpendicular magnetization are based on the spin-orbital coupling which includes ferromagnetic/noble-metal multilayers and strained magnetic ultrathin films. However, a new possibility for achieving perpendicular magnetization is through exchange-coupled ferromagnetic/antiferromagnetic bilayers or multilayers. Here we have proposed a new concept for establishing perpendicular magnetization via antiferromagnteic-ferromagnetic exchange coupling. "This finding is also beyond current physics of antiferromagnteicferromagnetic exchange coupling, indicating that the well –known exchange bias is only one of two effects."

Microscopic magnetic behavior of supported nanoparticles is strongly correlated with their functionalities, especially in data storage and biological applications, but still needs to be clarified. We studied nanoscale magnetic configurations of Fe nanoparticle assemblies using scanning electron microscopy with polarization analysis. The flux closure domain configurations and the reduced magnetic correlation length $(\ensuremath{\sim}250\text{ }\text{nm})$, relative to the conventional thin films, are determined. Quantitative analysis indicates the magnetic interaction energy to be 80--99 meV, close to the magnetic dipolar coupling energy. These direct observations evidence the aforereported simulations and will be valuable for fabricating magnetic nanoparticle assemblies with the desired magnetic properties.

Studies of magnetic domain and magnetic anisotropy in collected nanoparticles are crucial for both understanding interparticle interaction and engineering in applications. In order to characterize the microscopic surface morphology and the nanoscale magnetic domain structure of Fe nanoparticles, a scanning tunneling microscope and a scanning electron microscope with polarization analysis (SEMPA) were used in our experiment. For the coverage of 9–13 monolayers (MLs) Fe deposited on Al2O3/NiAl(100), circular and well-separated nanoparticles were grown. As the coverage increased up to 23–33 ML, these Fe nanoparticles started to coalesce and form elongated islands. Therefore a transition from isotropic to anisotropic in-plane magnetism was observed. Our proposed uniaxial magnetic anisotropy models effectively explain the azimuthal angle dependent two-step hysteresis loops. Moreover, the in situ measured SEMPA images clearly show the coverage dependent evolution of magnetic domain structure. Variations in inte...

Soft magnetic tip was utilized to be the probe of spin-polarized scanning tunneling microscopy. It was demonstrated that the spin contrast can be reversed by in situ switching tip magnetization through varying tip-substrate distance for resolving perpendicular magnetic domain images. With this in situ magnetization direction switching of the soft magnetic tip, it is conceivable to separate magnetic from chemical and topographic contributions without applying external magnetic field. This provides an effective tool for the study of complex magnetic spin structures with various nonmagnetic impurities or compositions involved.

Self-assembled one-dimensional nanostripes on the single-crystalline Al2O3 domains are found to be the nucleation sites of nanoparticles through an enhanced density of states observed by the scanning tunneling microscopy and spectroscopy. Bias-dependent topographic images and the conductivity spectra indicate that these nanostripes have both enhanced occupied and unoccupied states within the oxide bandgap. These more metallic nanostripes have stronger electronically trapping ability than the oxide domain, which can be used as a one-dimensional electronically self-patterned template for the guided growth of nanostructures.

We report a method of magnetic probe fabrication using ring-shaped and iron-coated tungsten wire for spin-polarized scanning tunneling microscopy. Magneto-optic Kerr effect measurement on the probe front end shows that by controlling the saturating field direction, we can fix the probe magnetization in the specific in-plane direction. The ring is applied to the scanning tunneling microscopy and spectroscopy experiment on 6.8 ML Mn∕Fe(001), and spin contrast in the in-plane direction is demonstrated.

The influence of in-plane and canted magnetic fields on spin spirals and skyrmions in atomic bilayer islands of palladium and iron on an Ir(111) substrate is investigated by scanning tunnelling microscopy at low temperatures. It is shown that the spin spiral propagation direction is determined by the island's border which can be explained by equilibrium state calculations on a triangular lattice. By application of in-plane fields, the spin spiral reorientates its propagation direction and becomes distorted, thereby allowing a proof for its cycloidal nature. Furthermore, it is demonstrated that the skyrmions' shape is distorted in canted fields which allows to determine the sense of magnetisation rotation as enforced by the interfacial Dzyaloshinskii-Moriya interaction., 14 pages, 7 figures