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V. S. Stepanyuk

Publications and source records attributed to V. S. Stepanyuk.

10 recordsLinked to original sources
arXiv2015

Effects of Interatomic Coupling on Magnetic Anisotropy and Order of Spins on Metallic Surfaces

Both quantum and classical behavior of single atomic spins on surfaces is determined by the local anisotropy of adatoms and their coupling to the immediate electronic environment. Yet adatoms seldom reside on surfaces alone and it is generally acknowledged that substrated-mediated interactions can couple single spins among each other impacting their magnetic behavior. Here we show that also magnetic anisotropy, which is usually considered to be a constant determined by the local crystal field, can be extremely sensitive to such interactions. By the example of Co dimers on Cu(001) and Pt(001) surfaces we highlight the intricate interplay of exchange coupling and magnetic anisotropy providing a much sought possibility to tune the latter through deliberate adjustment of the adatoms' separation. As a technologically relevant implication we demonstrate the impact of such emergent non-local anisotropy on the hysterectic properties of single-atom magnetization curves.

cond-mat.mtrl-sci↗
arXiv2015

Ferromagnetism of Pd(001) substrate induced by Antiferromagnetic CoO

Our first-principles study has revealed unexpected spin polarization of the Pd(001) substrate in contact with antiferromagnetic CoO overlayers. We give an evidence that the ferromagnetism of Pd is caused by the zigzag positions of Co atoms with respect to the Pd interface, resulted from the lattice-mismatch driven structural relaxation. Thanks to the itinerant nature of its 4d electrons, we see that the ferromagnetic properties of Pd are highly sensitive to the local environment and can be enhanced further by increasing the thickness of CoO overlayer film or/and by applying an additional uniaxial pressure along c-axis exerted externally on the bottom layers of the Pd substrate. Our finding provides new functionality for the interfacial moments of the CoO/Pd system, which can be accessed experimentally, e.g., by the magneto-optical Kerr effect (MOKE) or/and by element-resolved X-ray magnetic circular dichroism (XMCD) measurement.

cond-mat.mtrl-sci↗
arXiv2008

Manipulating magnetism and conductance of an adatom-molecule junction on metal surfaces: ab initio study

The state of the art ab initio calculations reveal the effect of a scanning tunnelling microscopy tip on magnetic properties and conductance of a benzene-adatom sandwich on Cu(001). We concentrate on a benzene-Co system interacting with a Cr tip. Our studies give a clear evidence that magnetism and conductance in molecule-adatom junctions can be tailored by the STM tip. Varying the tip-substrate distance the magnetic moment of the Co adatom can be switched on/off. The interplay between spin-polarized electron transport through the junction and its magnetic properties is demonstrated. A spin-filter effect in the junction is predicted.

cond-mat.mtrl-sci↗
arXiv2008

Tailoring exchange interactions in engineered nanostructures: Ab initio study

We present a novel approach to spin manipulation in atomic-scale nanostructures. Our ab initio calculations clearly demonstrate that it is possible to tune magnetic properties of sub-nanometer structures by adjusting the geometry of the system. By the example of two surface-based systems we demonstrate that (i) the magnetic moment of a single adatom coupled to a buried magnetic Co layer can be stabilized in either a ferromagnetic or an antiferromagnetic configuration depending on the spacer thickness. It is found that a buried Co layer has a profound effect on the exchange interaction between two magnetic impurities on the surface. (ii) The exchange interaction between magnetic adatoms can be manipulated by introducing artificial nonmagnetic Cu chains to link them.

cond-mat.mes-hall↗
arXiv2007

Size-dependent Surface States on Strained Cobalt Nanoislands on Cu(111)

Low-temperature scanning tunneling spectroscopy over Co nanoislands on Cu(111) showed that the surface states of the islands vary with their size. Occupied states exhibit a sizeable downward energy shift as the island size decreases. The position of the occupied states also significantly changes across the islands. Atomic-scale simulations and ab inito calculations demonstrate that the driving force for the observed shift is related to size-dependent mesoscopic relaxations in the nanoislands.

cond-mat.mtrl-sci↗
arXiv2007

Exchange interaction between single magnetic adatoms

The magnetic coupling between single Co atoms adsorbed on a copper surface is determined by probing the Kondo resonance using low-temperature scanning tunneling spectroscopy. The Kondo resonance, which is due to magnetic correlation effects between the spin of a magnetic adatom and the conduction electrons of the substrate, is modified in a characteristic way by the coupling of the neighbouring adatom spins. Increasing the interatomic distance of a Cobalt dimer from 2.56A to 8.1A we follow the oscillatory transition from ferromagnetic to antiferromagnetic coupling. Adding a third atom to the antiferromagnetically coupled dimer results in the formation of a collective correlated state.

cond-mat.str-el↗
arXiv2005

Ab initio study of mirages and magnetic interactions in quantum corrals

The state of the art ab initio calculations of quantum mirages,the spin-polarization of surface-state electrons and the exchange interaction between magnetic adatoms in Cu and Co corrals on Cu(111) are presented. We find that the spin-polarization of the surface-state electrons caused by magnetic adatoms can be projected to a remote location and can be strongly enhanced in corrals compared to an open surface.Our studies give a clear evidence that quantum corrals could permit to tailor the exchange interaction between magnetic adatoms at large separations. The spin-polarization of surface-state electrons at the empty focus in the Co corral used in the experimental setup of Manoharan et al., (Nature 403, 512 (2000)) is revealed.

cond-mat.mtrl-sci↗
arXiv2004

Ab initio approach for atomic relaxations in supported magnetic clusters

We present a newly developed scheme for atomic relaxations of magnetic supported clusters. Our approach is based on the full potential Korringa-Kohn-Rostoker Green's function method and the second moment tight-binding approximation for many-body potentials. We demonstrate that only a few iterations in ab initio calculations are necessary to find an equilibrium structure of supported clusters. As an example, we present our results for small Co clusters on Cu(001). Changes in electronic and magnetic states of clusters due to atomic relaxations are revealed.

cond-mat.mtrl-sci↗
arXiv2004

Long-range electronic interactions between adatoms on transition metal surfaces

Ab initio calculations of surface-state mediated interactions between Cu adatoms on transition metal surfaces are presented. We concentrate on Co/Cu(111) and Co(0001) substrates and compare results with our calculations for Cu(111). Our studies show that surface states of Co/Cu(111) and Co(0001) are spin-polarized. We reveal that long-range interactions between adatoms are mainly determined by sp-majority states. In contrast to Cu(111) and Co/Cu(111), the interaction between adatoms on Co(0001) is strongly suppressed at large adsorbate separations.

cond-mat.mtrl-sci↗