arXiv subjects

V. V. Fisun

Publications and source records attributed to V. V. Fisun.

44 records · Page 3Linked to original sources

arXiv2008

Spin dynamics in point contacts to single ferromagnetic films

Excitation of magnons or spin-waves driven by nominally unpolarized transport currents in point contacts of normal and ferromagnetic metals is probed by irradiating the contacts with microwaves. Two characteristic dynamic effects are observed: a rectification of off-resonance microwave current by spin-wave nonlinearities in the point contact conductance, and a resonant stimulation of spin-wave modes in the nano-contact core by the microwave field. These observations provide a direct evidence that the magnetoconductance effects observed are due to GHz spin dynamics at the ferromagnetic interface driven by the spin transfer torque effect of the transport current.

cond-mat.mtrl-sci↗

arXiv2007

Surface Spin-valve Effect

We report an observation of spin-valve like hysteresis within a few atomic layers at a ferromagnetic interface. We use phonon spectroscopy of nanometer sized point contacts as an in-situ probe to study the mechanism of the effect. Distinct in energy phonon peaks for contacts with dissimilar nonmagnetic outer electrodes allow to localize the observed spin switching to the top or bottom interfaces for nanometer thin ferromagnetic layers. The mechanism consistent with our data is energetically distinct atomically thin surface spin layers that can form current or field driven surface spin-valves within a single ferromagnetic film.

cond-mat.mes-hall↗

arXiv2006

Magnetic unipolar features in con- ductivity of point contacts between normal and ferromagnetic d-metals (Co, Ni, Fe)

In nanocontacts between normal and ferromagnetic metals (N--F) abrupt changes of the order of 1% are detected in differential resistance, dV/dI(V), versus bias voltage, V, on achieving of high current densities, ~10^9 A/cm^2. These features in dV/dI(V) are observed when the electron flow is directed from the nonmagnetic metal into the ferromagnet and connected with magnetization excitations in the ferromagnet induced by the current. Applying an external magnetic field leads to a shift of the observed features to higher biasing current, confirming the magnetic nature of the effect. Such effects are observed for the non-ballistic (not spectral) regime of current flow in the nanocontacts. Thus, the current induced magneto-conductance effects in multilayered N--F structures (nanopillars) extensively studied in the recent literature have much more general character and can be stimulated by elastic electron scattering at single N--F interfaces.

cond-mat.other↗

arXiv2005

Spectroscopy of phonons and spin torques in magnetic point contacts

Phonon spectroscopy is used to investigate the mechanism of current-induced spin torques in nonmagnetic/ferromagnetic (N/F) point contacts. Magnetization excitations observed in the magneto-conductance of the point contacts are pronounced for diffusive and thermal contacts, where the electrons experience significant scattering in the contact region. We find no magnetic excitations in highly ballistic contacts. Our results show that impurity scattering at the N/F interface is the origin of the new single-interface spin torque effect.

cond-mat.mtrl-sci↗

arXiv2003

Remarks about the Zeeman splitting in quantum dots and single atom transistors

An empirical formula is proposed to calculate the Kondo temperature in quantum point contacts from the Zeeman splitting. A similar formula was used in the point-contact spectroscopy (PCS) method to obtain from the Zeeman splitting of the Kondo peak in the characteristics of the classical Kondo alloys AuFe and CuMn [1]. Using this formula, it is possible to find the Kondo temperature taking into account the temperature of the experiment and Lande factor of the compounds.

cond-mat.str-el↗

arXiv2002

Study of the electron-phonon interaction in metal diborides MeB_2 (Me=Zr, Nb, Ta, Mg) by point-contact spectroscopy

We review investigations of the electron-phonon interaction (EPI) in metal diborides MeB_2 (Me=Zr, Nb, Ta, Mg) by point-contact (PC) spectroscopy. For transition metal compounds the PC EPI functions were recovered and EPI parameter $λ\lesssim 0.1$ were estimated. The data are consistent with the measured surface phonon dispersion curves. The low $λ$ value questions some reports about superconductivity in these compounds. Contrary, EPI in superconducting MgB_2 films manifests also in the PC spectra itself by virtue of an elastic EPI contribution to the excess current determined by the energy dependence of the superconducting order parameter. To analyse the phonon features in the PC spectra of MgB$_2$ a two-band model is exploited and the proximity effect in the {\bf k}-space is suggested.

cond-mat.supr-con↗

arXiv2002

Phonon structure in I-V characteristic of MgB$_{2}$ point-contacts

The search of the phonon structure at the above-gap energies was carried out for $d^{2}V/dI^{2}(V)$ spectra of MgB$_{2}$ point contacts with a normal metal. The two-band model is assumed not only for the gap structure in $dV/dI(V)$-characteristics, but also for phonons in $d^{2}V/dI^{2}(V)$ point-contact spectra, with up to the maximum lattice vibration energy. Since the current is carried mostly by charges of 3D-band, whereas the strong electron-phonon interaction occurs in 2D-band, we observe the phonon peculiarities due to ''proximity'' effect in {\it k}-space, which depends on the variation of interband coupling through the elastic scattering.

cond-mat.supr-con↗

arXiv2000

Enhancement of Kondo Temperature in Nanometer-Size Point Contacts

Point-contact spectroscopy is applied to study the energy dependence of paramagnetic impurities in noble metals. The samples are in the form of the so-called "mechanically controllable break-junctions" where the investigated piece of alloy makes a nanowire connecting two bulk electrodes.The lateral dimensions of the bridge are of the order of a few nm and can be continuously changed. Three qualitative dependences manifest the size effect while decreasing the contact diameter: 1) Intensity of Kondo peak due to Kondo scattering in point-contact spectra decreases slower than the nonlinearities due to phonon scatterings, 2) The width of the Kondo peak becomes broder, and 3) Due to the Zeeman energy, the splitting of Kondo peak in external and internal (for a spin glass) fields, is suppressed. Explanation of the phenomena is given in terms of the theory of Zarand and Udvardi where the local density of states (LDOS) of conduction electron fluctuates strongly inside a nanowire due to interference of electronic states. Since Kondo effect is a local probe of LDOS, the impurities located close to the maxima of LDOS show the increase of the Kondo temperature and give the primary contribution to the contact resistance.

cond-mat.mes-hall↗