[show abstract][hide abstract] ABSTRACT: Domain wall propagation has been measured in continuous, weakly disordered, quasi-two-dimensional, Ising-like magnetic layers that are subject to spatially periodic domain wall pinning potentials. The potentials are generated non-destructively using the stray magnetic field of ordered arrays of magnetically hard [Co/Pt]_m nanoplatelets, which are patterned above and are physically separated from the continuous magnetic layer. The effect of the periodic pinning potentials on thermally activated domain wall creep dynamics is shown to be equivalent, at first approximation, to that of a uniform, effective retardation field, H_ret, which acts against the applied field, H. We show that H_ret depends not only on the array geometry but also on the relative orientation of H and the magnetization of the nanoplatelets. A result of the latter dependence is that wall-mediated hysteresis loops obtained for a set nanoplatelet magnetization exhibit many properties that are normally associated with ferromagnet/antiferromagnet exchange bias systems. These include a switchable bias, coercivity enhancement, and domain wall roughness that is dependent on the applied field polarity.
Journal of Applied Physics 02/2013; 113(102). · 2.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: The barrier thickness dependence of the resistance-area product for Fe/MgO/Fe(001) and Fe/FeO/MgO/Fe(001) samples is presented in this work. Our measurements provide evidence of Delta(1) Bloch states filtering in the presence of an oxygen monolayer at the Fe/MgO interface, in agreement with theoretical predictions. For the transmission probability, the oxygen monolayer is shown to form an additional barrier equivalent to two MgO monolayers. Unexpectedly, the interfacial oxygen strongly reduces the conductance in the antiparallel configuration of magnetizations, and has only a small effect on the tunnel magnetoresistance. (C) 2012 The Japan Society of Applied Physics
[show abstract][hide abstract] ABSTRACT: We report the direct measurement of the nonadiabatic component of the spin torque in domain walls. Our method is independent of both the pinning of the domain wall in the wire as well as of the Gilbert damping parameter. We demonstrate that the ratio between the nonadiabatic and the adiabatic components can be as high as 1, and explain this high value by the importance of the spin-flip rate to the nonadiabatic torque. In addition to their fundamental significance these results open the way for applications by demonstrating a significant increase of the spin torque efficiency.
[show abstract][hide abstract] ABSTRACT: The stray magnetic field of an array of hard ferromagnetic perpendicularly magnetized [Co/Pt]4 nanodots is used to nondestructively generate a periodic pinning potential for domain walls in an underlying [Pt/Co]2/Pt layer with perpendicular anisotropy. Pinning is evidenced using magneto-optical microscopy. The magnetic field (H) dependence of the average wall velocity in the presence of the periodic pinning potential is consistent with thermally activated creep, modified only by the addition of a uniform retarding field Hret, whose magnitude depends on the relative alignment of H and the dots' magnetizations.
[show abstract][hide abstract] ABSTRACT: All solid-state tunnel spectroscopy experiments performed on single-crystal Fe/MgO/Fe magnetic tunnel junctions show sharp features at 0.2 and 1.1 V. These peaks are observed on the electrical differential conductivity only in the antiparallel magnetic configuration and only for the voltage sign corresponding to the injection of electrons toward the bottom electrode. They are attributed to the conductivity of two different resonant states of the Fe(001)/MgO bottom interface. The analysis of the attenuation of these peaks as a function of the insulator thickness provides information on their symmetry.
Physical Review B 07/2008; 78(3). · 3.77 Impact Factor