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ABSTRACT: The electric (E) field control of magnetic properties opens the prospects of
an alternative to magnetic field or electric current activation to control
magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have
proven to be particularly sensitive to the influence of an E-field due to the
interfacial origin of their anisotropy. In these systems, E-field effects have
been recently applied to assist magnetization switching and control domain wall
(DW) velocity. Here we report on two new applications of the E-field in a
similar material : controlling DW nucleation and stopping DW propagation at the
edge of the electrode.
01/2013;
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ABSTRACT: Current-induced domain wall motion and magnetization dynamics in the CoFeB layer of CoFeB/Cu/Co nanostripes were studied using photoemission electron microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM). Quasi-static measurements show that current-induced domain wall motion in the CoFeB layer is similar to the one observed in the NiFe layer of NiFe/Cu/Co trilayers, although the threshold current densities for domain wall depinning are lower. Time-resolved XMCD-PEEM measurements are used as an efficient probe of domain wall depinning statistics. They also reveal that, during the application of current pulses, the CoFeB magnetization rotates in the direction transverse to the nanostripe. The corresponding tilt angles have been quantified and compared to analytical and micromagnetic calculations, highlighting the influence of magnetostatic interactions between the two magnetic layers on the magnetization rotation.
Journal of Physics Condensed Matter 01/2012; 24(2):024213. · 2.55 Impact Factor
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V Uhlíř, S Pizzini,
N Rougemaille,
V Cros,
E Jiménez,
L Ranno,
O Fruchart,
M Urbánek,
G Gaudin,
J Camarero,
C Tieg,
F Sirotti,
E Wagner,
J Vogel
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ABSTRACT: We have used time-resolved x-ray photoemission electron microscopy to investigate the magne-tization dynamics induced by nanosecond current pulses in NiFe/Cu/Co nanostripes. A large tilt of the NiFe magnetization in the direction transverse to the stripe is observed during the pulses. We show that this effect cannot be quantitatively understood from the amplitude of the Oersted field and the shape anisotropy. High frequency oscillations observed at the onset of the pulses are attributed to precessional motion of the NiFe magnetization about the effective field. We discuss the possible origins of the large magnetization tilt and the potential implications of the static and dynamic effects of the Oersted field on current-induced domain wall motion in such stripes.
02/2011;
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V. Uhlíř, S. Pizzini,
N. Rougemaille,
J. Novotný,
V. Cros,
E. Jiménez,
G. Faini,
L. Heyne,
F. Sirotti,
C. Tieg,
A. Bendounan,
F. Maccherozzi,
R. Belkhou,
J. Grollier,
A. Anane,
J. Vogel
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ABSTRACT: Very large average velocities, up to 600 m/s, have been found for domain-wall motion driven by 3-ns-long pulses of electric current in zero magnetic field in the NiFe layer of 200-nm-wide NiFe/Cu/Co nanowires. For longer pulses, the domain-wall motion is strongly hindered by pinning potentials. Dipolar interactions between the NiFe and Co layers caused by anisotropy inhomogeneities have been identified as the most important among the different potential sources of DW pinning. The domain-wall velocities increase with current density, but a substantial drop is observed at current densities above 4×1011 A/m2.
Phys. Rev. B. 06/2010; 81(22).
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Applied Physics Letters 10/2009; 95(17):179902-179902-1. · 3.84 Impact Factor
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ABSTRACT: Current-induced domain wall (DW) displacements in an array of ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly observed by wide field Kerr microscopy. DWs in all wires in the array were driven simultaneously and their displacement on the micrometer scale was controlled by the current pulse amplitude and duration. At the lower current densities where DW displacements were observed (j≤1.5×10<sup>12</sup> A / m <sup>2</sup>) , the DW motion obeys a creep law. At higher current density (j=1.8×10<sup>12</sup> A / m <sup>2</sup>) , zero-field average DW velocities up to 130±10 m / s were recorded.
Applied Physics Letters 01/2009; · 3.84 Impact Factor
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A. Manchon,
C. Ducruet,
L. Lombard,
S. Auffret,
B. Rodmacq,
B. Dieny, S. Pizzini,
J. Vogel,
V. Uhlir,
M. Hochstrasser,
G. Panaccione
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ABSTRACT: Extraordinary Hall effect and x-ray spectroscopy measurements have been performed on a series of Pt / Co /M Ox trilayers ( M= Al , Mg, Ta, etc.) in order to investigate the role of oxidation in the onset of perpendicular magnetic anisotropy at the Co /M Ox interface. It is observed that varying the plasma oxidation time modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. We focused on the influence of plasma oxidation on Pt/Co/AlOx perpendicular magnetic anisotropy. The interfacial electronic structure is analyzed via x-ray photoelectron spectroscopy measurements. It is shown that the maximum of out-of-plane magnetic anisotropy corresponds to the appearance of a significant density of Co–O bondings at the Co/AlOx interface.
Journal of Applied Physics 09/2008; · 2.17 Impact Factor
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ABSTRACT: We have used time-resolved x-ray magnetic circular dichroism combined with photoemission electron microscopy (XMCD-PEEM) to
investigate the layer-resolved microscopic magnetization reversal in FeNi/X/Co (with X=Cu, Al2O3) trilayer systems. These measurements were performed in pump-probe mode, synchronizing magnetic pulses with synchrotron x-ray
pulses. The good magnetic contrast observed for most samples reveals that in many cases the magnetization reversal is reproducible.
We have used the measurements to obtain domain wall propagation speeds as a function of applied magnetic field, and to investigate
the influence of domain wall interactions on the magnetic switching.
Applied Physics A 07/2008; 92(3):505-510. · 1.63 Impact Factor
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A. Manchon, S. Pizzini,
J. Vogel,
V. Uhlîr,
L. Lombard,
C. Ducruet,
S. Auffret,
B. Rodmacq,
B. Dieny,
M. Hochstrasser,
G. Panaccione
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ABSTRACT: X-ray spectroscopy measurements have been performed on a series of Pt/Co/AlOx trilayers to investigate the role of Co oxidation in the perpendicular magnetic anisotropy at the Co/AlOx interface. It is observed that varying the degree of oxidation modifies the magnetic properties of the Co layer, inducing a magnetic anisotropy crossover from in plane to out of plane. The microscopic structural properties are analyzed via x-ray photoelectron spectroscopy measurements. It is shown that increasing the oxidation time enhances the amount of interfacial oxide, which may be at the origin of perpendicular magnetic anisotropy.
Journal of Applied Physics 03/2008; 103(7):07A912-07A912-3. · 2.17 Impact Factor
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G. Ghiringhelli,
M. Bonfim,
N.B. Brookes,
J. Camarero,
K. Mackay,
F. Montaigne,
T. Neisius,
Ph. Ohresser,
S. Pascarelli,
F. Petroff, S. Pizzini,
A. Fontaine
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ABSTRACT: We have used the single bunch filling mode of the ESRF synchrotron to study the magnetisation reversal dynamics. It is a pump-probe
type of experiment in the time scale ranging from 1 ns to 1000 ns. In the presence of a constant magnetic field, a pulsed
magnetic field (pump) temporarily reverses the magnetisation; the x-ray pulse (probe), synchronised with the magnetic pulse,
comes with a known delay. By measuring the x-ray magnetic circular dichroism as a function of the delay between the two pulses
we can follow the magnetisation dynamics during and after the magnetic pulse. In magnetically heterogeneous samples the element
selectivity of XMCD allows us to disentangle the different contributions to the magnetic dynamics. The technique has been
implemented both in the soft and the hard x-ray regimes. We present some results on Co/Cu/NiFe spin valves and on Co/Al2O3/NiFe
tunnel junctions.
01/2008: pages 347-354;
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ABSTRACT: We have performed a layer-resolved, microscopic study of interactions between domain walls in two magnetic layers separated by a non-magnetic one, using high-resolution x-ray photoemission electron microscopy. Domain walls in the hard magnetic Co layer of a Co/Al2O3/FeNi trilayer with in-plane uniaxial anisotropy strongly modify the local magnetization direction in the soft magnetic FeNi layer. The stray fields associated with the domain walls lead to an antiparallel coupling between the local Co and FeNi moments. For domain walls parallel to the easy magnetization axis, this interaction is limited to the domain wall region itself. For strongly charged (head-on or tail-to-tail) walls, the antiparallel coupling dominates the interaction over radial distances up to several micrometres from the centre of the domain wall.
Journal of Physics Condensed Matter 10/2007; 19(47):476204. · 2.55 Impact Factor
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ABSTRACT: This paper describes the preparation and study of FeIr superlattices grown by molecular beam epitaxy. The samples were characterised by RHEED measurements, x-ray diffraction (XRD) and near-edge x-ray absorption spectroscopy (XAS). Electron diffraction shows that the surface structure of Fe on Ir is hexagonal up to a critical thickness of 3 ML and that the growth occurs layer by layer. An original method of thickness calibration by XRD on a series of FeIr superlattices is presented, which allows a precise determination of the distance of Fe planes. XRD measurements are in agreement with a ABCABC stacking sequence in the Fe films. Polarisation-dependent Fe K near-edge XAS indicate that the close-packed structure of Fe films, both in the plane and perpendicular to the hexagonal plane, is maintained up to a thickness of 5 ML of Fe. The critical thickness for superlattices is therefore larger than that of a "free" Fe film.
EPL (Europhysics Letters) 07/2007; 18(6):529. · 2.17 Impact Factor
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ABSTRACT: Soft x-ray resonant magnetic scattering has been used to investigate the element-selective microscopic magnetization reversal behavior of room temperature perpendicular exchange coupled ferromagnetic/antiferromagnetic (F/AF) systems and to study the role of the interfacial coupling strength on it. Different nucleation processes and domain size distributions along the decreasing and increasing branches of the reversal have been found. The size of the magnetic domains during reversal depends on both the F anisotropy and F/AF coupling strength, decreasing when one of them increases. Evidence of the exchange bias (coercivity enhancement) being induced by pinned (unpinned) uncompensated AF interfacial spins is also shown.
Applied Physics Letters 01/2007; · 3.84 Impact Factor
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ABSTRACT: We have studied the magnetization reversal dynamics of FeNi∕Al2O3∕Co magnetic tunnel junctions deposited on step-bunched Si substrates using magneto-optical Kerr effect and time-resolved x-ray photoelectron emission microscopy combined with x-ray magnetic circular dichroism (XMCD-PEEM). Different reversal mechanisms have been found depending on the substrate miscut angle. Larger terraces (smaller miscut angles) lead to a higher nucleation density and stronger domain wall pinning. The width of domain walls with respect to the size of the terraces seems to play an important role in the reversal. We used the element selectivity of XMCD-PEEM to reveal the strong influence of the stray field of domain walls in the hard magnetic layer on the magnetic switching of the soft magnetic layer.
Phys. Rev. B. 10/2006; 74(18).
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ABSTRACT: The dynamics of magnetic domain wall motion in the FeNi layer of a FeNi/Al2O3/Co trilayer has been investigated by a combination of x-ray magnetic circular dichroism, photoelectron emission microscopy, and a stroboscopic pump-probe technique. The nucleation of domains and subsequent expansion by domain wall motion in the FeNi layer during nanosecond-long magnetic field pulses was observed in the viscous regime up to the Walker limit field. We attribute an observed delay of domain expansion to the influence of the domain wall energy that acts against the domain expansion and that plays an important role when domains are small.
Physical Review Letters 04/2006; 96(9):097204. · 7.37 Impact Factor
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F Romanens, S Pizzini,
F Yokaichiya,
M Bonfim,
Y Pennec,
J Camarero,
J Vogel,
J Sort,
F Garcia,
B Rodmacq,
B Dieny
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ABSTRACT: Magnetization relaxation of exchange-biased (Pt∕Co)5∕Pt∕IrMn multilayers with perpendicular anisotropy was investigated by time-resolved Kerr microscopy. Magnetization reversal occurs by nucleation and domain wall propagation for both descending and ascending applied fields, but a much larger nucleation density is observed for the descending branch, where the field is applied antiparallel to the exchange bias field direction. These results can be explained by taking into account the presence of local inhomogeneities of the exchange bias field.
Physical Review B 10/2005; 72(13). · 3.69 Impact Factor
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ABSTRACT: The influence of magnetic anisotropy on nanosecond magnetization reversal in coupled FeNi∕Cu∕Co trilayers was studied using a photoelectron emission microscope combined with x-ray magnetic circular dicroism. In quasi-isotropic samples the reversal of the soft FeNi layer is determined by domain-wall pinning that leads to the formation of small and irregular domains. In samples with uniaxial magnetic anisotropy, the domains are larger and the influence of local interlayer coupling dominates the domain structure and the reversal of the FeNi layer.
Phys. Rev. B. 06/2005; 71(6).
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ABSTRACT: Magnetic relaxation measurements were carried out by magneto-optical Kerr effect on exchange biased (Pt/Co)5/Pt/FeMn multilayers with perpendicular anisotropy. In these films the coercivity and the exchange bias field vary with Pt spacer thickness, and have a maximum for 0.2 nm. Hysteresis loops do not reveal important differences between the reversal for ascending and descending fields. Relaxation measurements were fitted using Fatuzzo’s model, which assumes that reversal occurs by domain nucleation and domain wall propagation. For 2 nm thick Pt spacer (no exchange bias) the reversal is dominated by domain wall propagation starting from a few nucleation centers. For 0.2 nm Pt spacer (maximum exchange bias) the reversal is strongly dominated by nucleation, and no differences between the behaviour of the ascending and descending branches can be observed. For 0.4 nm Pt spacer (weaker exchange bias) the nucleation density becomes less important, and the measurements reveal a much stronger density of nucleation centers in the descending branch. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005
Physics of Condensed Matter 04/2005; 45(2):185-190. · 1.53 Impact Factor
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ABSTRACT: We have performed magnetic domain imaging with spatial, temporal, and layer resolution using x-ray photoelectron emission microscopy. The element selectivity of x-ray magnetic circular dichroism allows the magnetization dynamics of the different magnetic layers in spin-valve-like FeNi/Cu/Co trilayers to be studied separately, using the time structure of synchrotron radiation. The unique possibilities of this technique have been used to study the influence of the intrinsic magnetic properties of the different layers on the magnetization dynamics and the interlayer magnetic coupling. © 2004 American Institute of Physics.
Journal of Applied Physics 05/2004; 95(11):6533-6536. · 2.17 Impact Factor
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J Camarero,
Y Pennec,
J Vogel,
M Bonfim, S Pizzini,
F Ernult,
F Fettar,
F Garcia,
F Lançon,
L Billard,
B Dieny,
A Tagliaferri,
N B Brookes
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ABSTRACT: An in-plane perpendicular magnetic coupling between Ni80Fe20 and Co has been found in NiFe/NiO/Co trilayers for a NiO thickness ranging from 4 to 25 nm by magneto-optical Kerr effect and x-ray magnetic circular dichroism measurements. In the easy magnetization direction of the Co layer, the Co coercive field H(C) increases when the thickness of the NiO layer t(NiO) increases. Because of the coupling, H(C) is always larger than for NiO/Co bilayers with the same thicknesses. The saturation field of the NiFe layer H(S) decreases when t(NiO) increases, indicating a weakening of the coupling. Numerical simulations show that the presence of interface roughness combined with a small value of the NiO anisotropy can explain the observed 90 degrees coupling.
Physical Review Letters 08/2003; 91(2):027201. · 7.37 Impact Factor
