Staff directory

Marius Vasile Costache

Senior Researcher
Ramón y Cajal
marius.costache(ELIMINAR)@icn2.cat
Physics and Engineering of Nanodevices

Publications

2017

  • Spin precession in anisotropic media

    Raes B., Cummings A.W., Bonell F., Costache M.V., Sierra J.F., Roche S., Valenzuela S.O. Physical Review B; 95 (8, 085403) 2017. 10.1103/PhysRevB.95.085403. IF: 3.836

    We generalize the diffusive model for spin injection and detection in nonlocal spin structures to account for spin precession under an applied magnetic field in an anisotropic medium, for which the spin lifetime is not unique and depends on the spin orientation. We demonstrate that the spin precession (Hanle) line shape is strongly dependent on the degree of anisotropy and on the orientation of the magnetic field. In particular, we show that the anisotropy of the spin lifetime can be extracted from the measured spin signal, after dephasing in an oblique magnetic field, by using an analytical formula with a single fitting parameter. Alternatively, after identifying the fingerprints associated with the anisotropy, we propose a simple scaling of the Hanle line shapes at specific magnetic field orientations that results in a universal curve only in the isotropic case. The deviation from the universal curve can be used as a complementary means of quantifying the anisotropy by direct comparison with the solution of our generalized model. Finally, we applied our model to graphene devices and find that the spin relaxation for graphene on silicon oxide is isotropic within our experimental resolution. © 2017 American Physical Society.


2016

  • Determination of the spin-lifetime anisotropy in graphene using oblique spin precession

    Raes B., Scheerder J.E., Costache M.V., Bonell F., Sierra J.F., Cuppens J., Van De Vondel J., Valenzuela S.O. Nature Communications; 7 ( 11444) 2016. 10.1038/ncomms11444. IF: 11.329

    We determine the spin-lifetime anisotropy of spin-polarized carriers in graphene. In contrast to prior approaches, our method does not require large out-of-plane magnetic fields and thus it is reliable for both low-and high-carrier densities. We first determine the in-plane spin lifetime by conventional spin precession measurements with magnetic fields perpendicular to the graphene plane. Then, to evaluate the out-of-plane spin lifetime, we implement spin precession measurements under oblique magnetic fields that generate an out-of-plane spin population. We find that the spin-lifetime anisotropy of graphene on silicon oxide is independent of carrier density and temperature down to 150 K, and much weaker than previously reported. Indeed, within the experimental uncertainty, the spin relaxation is isotropic. Altogether with the gate dependence of the spin lifetime, this indicates that the spin relaxation is driven by magnetic impurities or random spin-orbit or gauge fields.


2015

  • Hot-Carrier Seebeck Effect: Diffusion and Remote Detection of Hot Carriers in Graphene

    Sierra J.F., Neumann I., Costache M.V., Valenzuela S.O. Nano Letters; 15 (6): 4000 - 4005. 2015. 10.1021/acs.nanolett.5b00922. IF: 13.592

    We investigate hot carrier propagation across graphene using an electrical nonlocal injection/detection method. The device consists of a monolayer graphene flake contacted by multiple metal leads. Using two remote leads for electrical heating, we generate a carrier temperature gradient that results in a measurable thermoelectric voltage VNL across the remaining (detector) leads. Due to the nonlocal character of the measurement, VNL is exclusively due to the Seebeck effect. Remarkably, a departure from the ordinary relationship between Joule power P and VNL, VNL ∼ P, becomes readily apparent at low temperatures, representing a fingerprint of hot-carrier dominated thermoelectricity. By studying VNL as a function of bias, we directly determine the carrier temperature and the characteristic cooling length for hot-carrier propagation, which are key parameters for a variety of new applications that rely on hot-carrier transport. (Figure Presented). © 2015 American Chemical Society.


2014

  • Fingerprints of inelastic transport at the surface of the topological insulator Bi 2 Se 3: Role of electron-phonon coupling

    Costache, M.V.; Neumann, I.; Sierra, J.F.; Marinova, V.; Gospodinov, M.M.; Roche, S.; Valenzuela, S.O. Physical Review Letters; 2014. 10.1103/PhysRevLett.112.086601. IF: 7.728


2013

  • Electrical detection of spin precession in freely suspended graphene spin valves on cross-linked poly(methyl methacrylate)

    Neumann, I.; Van De Vondel, J.; Bridoux, G.; Costache, M.V.; Alzina, F.; Torres, C.M.S.; Valenzuela, S.O. Small; 9 (1): 156 - 160. 2013. 10.1002/smll.201201194. IF: 7.823


  • Enhanced spin accumulation at room temperature in graphene spin valves with amorphous carbon interfacial layers

    Neumann, I.; Costache, M.V.; Bridoux, G.; Sierra, J.F.; Valenzuela, S.O. Applied Physics Letters; 2013. 10.1063/1.4820586. IF: 3.794


2012

  • Lateral metallic devices made by a multiangle shadow evaporation technique

    Costache, M.V.; Bridoux, G.; Neumann, I.; Valenzuela, S.O. Journal of Vacuum Science and Technology B: Microelectronics and Nanometer Structures; 30: 4. 2012. .


2011

  • Enhanced spin signal in nonlocal devices based on a ferromagnetic CoFeAl alloy

    Bridoux, G.; Costache, M. V.; Van de Vondel, J. ; Neumann, I.; Valenzuela, S. O. Applied Physics Letters; 2011. .


  • Generation of pure spin currents in a single electron transistor with a superconducting island

    Costache, M.V.; Valenzuela, S.O. Proceedings of SPIE - The International Society for Optical Engineering; 2011. 10.1117/12.890231 .


  • Magnon-drag thermopile

    Costache, M.V.; Bridoux, G.; Neumann, I.; Valenzuela, S.O. Nature Materials; 2011. .


  • Perpendicular switching of a single ferromagnetic layer induced by in-plane current injection

    Miron I.M., Garello K., Gaudin G., Zermatten P.-J., Costache M.V., Auffret S., Bandiera S., Rodmacq B., Schuhl A., Gambardella P. Nature; 476 (7359): 189 - 193. 2011. 10.1038/nature10309.

    Modern computing technology is based on writing, storing and retrieving information encoded as magnetic bits. Although the giant magnetoresistance effect has improved the electrical read out of memory elements, magnetic writing remains the object of major research efforts. Despite several reports of methods to reverse the polarity of nanosized magnets by means of local electric fields and currents, the simple reversal of a high-coercivity, single-layer ferromagnet remains a challenge. Materials with large coercivity and perpendicular magnetic anisotropy represent the mainstay of data storage media, owing to their ability to retain a stable magnetization state over long periods of time and their amenability to miniaturization. However, the same anisotropy properties that make a material attractive for storage also make it hard to write to. Here we demonstrate switching of a perpendicularly magnetized cobalt dot driven by in-plane current injection at room temperature. Our device is composed of a thin cobalt layer with strong perpendicular anisotropy and Rashba interaction induced by asymmetric platinum and AlO x interface layers. The effective switching field is orthogonal to the direction of the magnetization and to the Rashba field. The symmetry of the switching field is consistent with the spin accumulation induced by the Rashba interaction and the spin-dependent mobility observed in non-magnetic semiconductors, as well as with the torque induced by the spin Hall effect in the platinum layer. Our measurements indicate that the switching efficiency increases with the magnetic anisotropy of the cobalt layer and the oxidation of the aluminium layer, which is uppermost, suggesting that the Rashba interaction has a key role in the reversal mechanism. To prove the potential of in-plane current switching for spintronic applications, we construct a reprogrammable magnetic switch that can be integrated into non-volatile memory and logic architectures. This device is simple, scalable and compatible with present-day magnetic recording technology. © 2011 Macmillan Publishers Limited. All rights reserved.


2010

  • All magnesium diboride Josephson junctions with MgO and native oxide barriers

    Costache, M.V. ; Moodera, J.S. Applied Physics Letters; 2010. .


  • Experimental spin ratchet

    Costache, M.V.; Valenzuela, S.O. SCIENCE; 330: 1645 - 1648. 2010. 10.1126/science.1196228.