Monchesky, Ted
Permanent URI for this collectionhttps://hdl.handle.net/10222/22098
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Item Open Access Direct observation of remanent magnetic states in epitaxial fcc Co small disks(2003-04) Vaz, CAF; Lopez-Diaz, L.; Klaui, M.; Bland, JAC; Monchesky, TL; Unguris, J.; Cui, Z.No abstract available.Item Open Access Role of interfaces in the magnetoresistance of Au/Fe/Au/Fe multilayers(APS through AIP, 2003-02/01) Weinberger, P.; Zabloudil, J.; Hammerling, R. H.; Szunyogh, L.; Monchesky, T. L.; Heinrich, B.By using the fully relativistic spin-polarized screened Korringa-Kohn-Rostoker method and the corresponding Kubo-Greenwood equation resistivities and the giant magnetoresistance are evaluated for Fe/Au/Fe/Au spin valves assuming both bcc-like Fe and fcc-Au leads. The theoretically obtained values for a spacer thickness of 7 monolayers of Au are in a rather good agreement with the corresponding experimental data. These data, in particular the temperature dependence of the resistivities reported in here, are analyzed with respect to the experimental setup and related to the theoretical models assumed. Since in the theoretical calculations interdiffused interfaces are taken into account by means of the inhomogeneous coherent potential approximation, the role of the interfaces in the magnetoresistance of this system can be discussed rigorouslyItem Open Access Extended elliptic skyrmion gratings in epitaxial MnSi thin films(2012-10) Wilson, M. N.; Karhu, E. A.; Quigley, A. S.; Roessler, U. K.; Butenko, A. B.; Bogdanov, A. N.; Robertson, M. D.; Monchesky, T. L.No abstract available.Item Open Access Magnetic properties of Co/GaAs(110)(APS through AIP, 2006-12/15) Monchesky, T. L.; Unguris, J.We observed three magnetic states of an ultrathin, atomically well-ordered Co film grown on a cleaved GaAs(110) substrate. For a Co thickness less than 3.4 monolayers (ML), we find a ferromagnetically dead layer associated with the formation of interfacial Co2GaAs. For thicknesses greater than 4.1 ML, the Co film grows with a bcc structure that contains 6 at. % Ga. The films are ferromagnetic with an easy axis along the 110] direction. This magnetic state persists up to a thickness of 7 ML, at which point an abrupt in-plane spin-reorientation transition reorients the magnetization along the 001] directionItem Open Access Magnetoresistance and magnetic properties of Fe/Cu/Fe/GaAs(100)(APS through AIP, 1999-10/01) Monchesky, T. L.; Heinrich, B.; Urban, R.; Myrtle, K.; Klaua, M.; Kirschner, J.A procedure for growth of smooth As free Fe surfaces on (46)-GaAs(100) is presented. Ferromagnetic resonance (FMR) revealed that the Fe films have anisotropies equal to bulk Fe, modified only by interface anisotropies. The Fe films served as templates for the growth of epitaxial Fe/Cu/Fe trilayers which were subsequently characterized by FMR, magneto-optical Kerr effect, and magnetoresistance. At room temperature, films coupled through a 13.2-ML Cu spacer exhibited 2.0% giant magnetoresistance and 0.3% anisotropic magnetoresistance. The results showed that the interlayer exchange coupling for a 13.2-ML Cu spacer could not be described by bilinear and biquadratic contributions alone. A different coupling, which varied as cosine cubed of the angle between the magnetizations of the Fe films, was required to explain the data (bicubic exchange coupling)Item Open Access Chiral modulations and reorientation effects in MnSi thin films(2012-03) Karhu, E. A.; Roessler, U. K.; Bogdanov, A. N.; Kahwaji, S.; Kirby, B. J.; Fritzsche, H.; Robertson, M. D.; Majkrzak, C. F.; Monchesky, T. L.No abstract available.Item Open Access Direct observation of spin configurations and classification of switching processes in mesoscopic ferromagnetic rings(2003-10) Klaui, M.; Vaz, CAF; Bland, JAC; Monchesky, TL; Unguris, J.; Bauer, E.; Cherifi, S.; Heun, S.; Locatelli, A.; Heyderman, LJ; Cui, Z.No abstract available.Item Open Access Growth, structure, electronic, and magnetic properties of MgO/Fe(001) bilayers and Fe/MgO/Fe(001) trilayers(2001-10) Klaua, M.; Ullmann, D.; Barthel, J.; Wulfhekel, W.; Kirschner, J.; Urban, R.; Monchesky, TL; Enders, A.; Cochran, JF; Heinrich, B.No abstract available.Item Open Access Spin-dependent transport in Fe and Fe/Au multilayers(APS through AIP, 2005-06/01) Monchesky, T. L.; Enders, A.; Urban, R.; Myrtle, K.; Heinrich, B.; Zhang, X. -G; Butler, W. H.; Kirschner, J.In situ resistance measurements of epitaxial Fe layers and Au/Fe bilayers were used to quantify the scattering in giant magnetoresistance (GMR) spin valve structures. The semiclassical Boltzmann transport equation, incorporating first-principles local density functional calculations, fitted the thickness dependence of the conductivity. Fits to the data indicate that Fe has a large spin asymmetry with bulk relaxation times =3.010-14 s and =2.510-15 s. These give a conductivity equal to that of bulk Fe. The interface scattering from the Fe/GaAs, the Fe/vacuum, and the Au/vacuum interfaces is purely diffuse. This is in contrast to the high electron reflection coefficients determined from kinematical calculations using scanning tunneling microscope images. Fits to conductivity measurements of Au/Fe/GaAs(001) indicate that the Au films have the conductivity of bulk material modified only by interface scattering. The GMR of Au/Fe/Au/Fe/GaAs(001) structures is 1.8% at room temperature and 2.9% at 10 K. The magnetoresistance is reduced by the presence of partial diffuse scattering at the inner interfaces, as indicated by the fits to both the GMR and the Au conductivity. The GMR in Fe/Au structures is intrinsically low due to a large electron band mismatch between Au and Fe band structuresItem Open Access Distorted iron films on GaAs(001)-(4x6)(2000-07) Gordon, RA; Crozier, ED; Jiang, DT; Monchesky, TL; Heinrich, B.No abstract available.Item Open Access Helical magnetic order in MnSi thin films(American Physical Society, 2011-08/01) Karhu, E. A.; Kahwaji, S.; Robertson, M. D.; Fritzsche, H.; Kirby, B. J.; Majkrzak, C. F.; Monchesky, T. L.We present a study of the magnetic structure of crystalline MnSi(111) thin films grown by molecular beam epitaxy. A combination of polarized neutron reflectometry (PNR) and superconducting quantum interference device magnetometry show that the films have helical magnetic order with a pitch vector Q along the film normal. The helix wavelength of 2/Q=13.90.1 nm is found to be independent of thickness below 40 nm. PNR shows that the magnetic structure has both left-handed and right-handed chiralities due to the presence of inversion domains observed by transmission electron microscopy.Item Open Access Structure and magnetic properties of MnSi epitaxial thin films(American Physical Society, 2010-11/01) Karhu, E.; Kahwaji, S.; Monchesky, T. L.; Parsons, C.; Robertson, M. D.; Maunders, C.We report on the correlation between the magnetic and structural properties of epitaxial MnSi (111) thin films grown by solid-phase epitaxy on Si (111) substrates. The Si (111) substrate, with a surface unit cell that is 3.0% larger than that of MnSi, causes an in-plane tensile strain in the film that is partially relaxed due to the presence of misfit dislocations located at the interface. However, the out-of-plane strain has a nonmonotonic dependence on thickness that is attributed to changes in the elastic constants of the film. The thickness dependence of the Curie temperature correlates strongly with strain and reaches a maximum of TC=43 K, a value that is 46% greater than the bulk value of TC=29.5 K. Although the films have a strong epitaxial relationship, 110]MnSi112]Si, there are inversion domains in the film due to the noncentrosymmetric crystal structure of MnSi. The presence of these domains implies that there are two magnetic chiralities, which likely contribute to the observed glassy magnetic response of the films.Item Open Access Local structure and magnetic properties of B2- and B20-like ultrathin Mn films grown on Si(001)(American Physical Society, 2012-01/01) Kahwaji, S.; Gordon, R. A.; Crozier, E. D.; Monchesky, T. L.The structural and magnetic properties of ultrathin Mn layers deposited onto Si(001) by molecular beam epitaxy at low temperature are reported. X-ray absorption fine structure studies reveal that the structure of the silicide layer that forms depends on the growth temperature of the capping layer. A capping layer grown at 200C on 0.35-monolayer (ML) Mn results in a metastable MnSi phase with a B2-like (CsCl) structure, whereas a cap grown at room temperature on 0.5 ML followed by annealing at 200C produces a lower coordinated MnSi phase with a B20-like structure. Increasing the Mn thickness from 0.5 to 4 monolayers does not trigger a structural transformation but drives the structure closer to MnSi-B20. The sample with B2-like structure has the largest Mn magnetic moment of 0.33 B/Mn at T= 2 K, and a Curie temperature TC above 250 K. MnSi-B20 layers showed lower moments and much lower TC's, in line with those reported for MnSi-B20 thin films.