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An analytical model was developed to describe the current induced domain wall (DW) dynamics of a Bloch DW in the presence of an external transverse magnetic field. The model takes into account the DW deformation and the magnetization tilting in the domain. The model is compared to the results of micromagnetic simulation and an excellent agreement is obtained. In the steady state regime, the model shows that the domain tilting does not change the DW mobility. An external or current induced transverse magnetic field such as the Oersted or Rashba field can prevent the Walker breakdown leading to a higher domain wall velocity. [ABSTRACT FROM AUTHOR]

We employ a scanning nitrogen-vacancy-center microscope to perform stray field imaging of bubble magnetic domains in a perpendicularly magnetized Pt/Co/AlOx trilayer with 6Å of Co. The stray field created by the domain walls is quantitatively mapped with few-nanometer spatial resolution, with a probe-sample distance of about 100nm. As an example of application, we show that it should be possible to determine the Bloch or Néel nature of the domain walls, which is of crucial importance to the understanding of current-controlled domain wall motion. [ABSTRACT FROM AUTHOR]

Current induced domain wall (DW) motion in perpendicularly magnetized nanostripes in the presence of spin orbit torques is studied. We show using micromagnetic simulations that the direction of the current induced DW motion and the associated DW velocity depend on the relative values of the field like torque (FLT) and the Slonczewski like torques (SLT). The results are well explained by a collective coordinate model which is used to draw a phase diagram of the DW dynamics as a function of the FLT and the SLT. We show that a large increase in the DW velocity can be reached by a proper tuning of both torques. [ABSTRACT FROM AUTHOR]

Submicron magnetic tunnel junctions exhibiting perpendicular magnetic anisotropy have been prepared by sputtering. They associate a hard and a soft electrode based on Co/Pt multilayers, separated by an amorphous alumina barrier. The soft electrode is either free or exchange biased by an antiferromagnetic layer. The magnetoresistance ratio reaches 8% at room temperature after patterning junctions with diameter down to 200 nm. The macroscopic magnetic properties were investigated by extraordinary Hall effect and conventional magnetometry measurements. The magnetic moments of both electrodes are out of plane. Two well-separated switching fields allow the realization of well-defined parallel and antiparallel configurations of the magnetizations. [ABSTRACT FROM AUTHOR]

Controlled propagation speed of individual magnetic domains in metal channels at the room temperature is obtained via the non-volatile field effect associated with the switchable polarization of P(VDF-TrFE) (polyvinylidene fluoride-trifluoroethylene) ferroelectric polymer. Polarization domains directly written using conducting atomic force microscope probe locally accelerate/decelerate the magnetic domains in the 0.6nm thick Co film. The change of the magnetic domain wall velocity is consistent with the magnetic anisotropy energy modulation through the polarization upward/downward orientation. Excellent retention is observed. The demonstrated local non-destructive and reversible change of magnetic properties via rewritable patterning of ferroelectric domains could be attractive for exploring the ultimate limit of miniaturization in devices based on ferromagnetic/ferroelectric bilayers. [ABSTRACT FROM AUTHOR]

The influence of the microstructure on the exchange bias properties of antiferromagnetic/ferromagnetic submicronic dots was investigated in arrays of IrMn/Co square dots of lateral dimensions ranging between 200 and 50�nm. IrMn grain size and distributions were tuned by changing the Cu buffer layer or IrMn thicknesses. Exchange bias variability was analysed through focused Kerr measurements on small groups of dots. The average exchange bias field in the patterned samples have similar values as in full sheet samples and with similar variations versus Cu and IrMn thicknesses. Concerning the exchange bias variability, an increase in variability was observed in the patterned samples caused by grain cutting at the dot edges during the patterning process. This increase in exchange bias variability is observed to be even more important in samples having large average grain sizes, particularly for small dots. These effects are correlated with the grain size distributions on full sheet samples. [ABSTRACT FROM AUTHOR]

Spin filtering effects in nano-pillars of Fe-MgO-Fe single crystalline magnetic tunnel junctions are explored with two different sample architectures and thin MgO barriers (thickness: 3-8 monolayers). The two architectures, with different growth and annealing conditions of the bottom electrode, allow tuning the quality of the bottom Fe/MgO interface. As a result, an interfacial resonance states (IRS) is observed or not depending on this interface quality. The IRS contribution, observed by spin polarized tunnel spectroscopy, is analyzed as a function of the MgO barrier thickness. Our experimental findings agree with theoretical predictions concerning the symmetry of the low energy (0.2 eV) interfacial resonance states: a mixture of Δ1-like and Δ5-like symmetries. [ABSTRACT FROM AUTHOR]

We investigated the magnetic switching of MgO/Co/Pt pillars with perpendicular magnetic anisotropy, for lateral pillar sizes from 30 μm to 2 lm and for Co layer thicknesses between 1.8 and 2.6 nm. For large pillars, both the coercivity and the remanent magnetization decrease for increasing Co thickness. For all Co thicknesses, the coercivity strongly increases upon decreasing the pillar size. A comparison with micromagnetic simulations shows that the change in coercivity is determined by size-dependent demagnetizing effects. Our results show that small pillars with perpendicular magnetization and a tunable coercivity can be fabricated from continuous layers with in-plane magnetization. [ABSTRACT FROM AUTHOR]

Non-volatile ferroelectric control of magnetic domains has been demonstrated in ultra-thin cobalt layers at room temperature. The sensitivity of magnetic anisotropy energy to the electronic structure in a few atomic layers adjacent to the interface allows for ferroelectric control of coercivity and magnetic domain dynamics. These effects have been monitored and quantified using magneto-optical Kerr effect. In particular, the regimes, where the ferroelectric domains enhance/inhibit the magnetic domain nucleation or increase/reduce domain wall velocity, have been explored. Thus, non-destructive and reversible ferroelectric domain writing provides a tool to define the magnetic domain paths, create nucleation sites, or control domain movement. [ABSTRACT FROM AUTHOR]

Finite size effects on the exchange-bias properties of patterned antiferromagnetic/ferromagnetic (IrMn/Co) nanodots were investigated experimentally and by numerical simulations. Both the dot lateral dimension (200 × 200 nm2-50 × 50 nm2) and ferromagnetic layer thickness (2-25 nm) were varied. Two different behaviours were observed: single-shifted loops with coherent reversal for thin Co layers and double-shifted loops via a multidomain state during magnetization reversal for thicker Co. Atomistic simulations including magnetostatic interactions confirmed the existence of these two different regimes. MOKE measurements, focused on few dots, allowed a quantitative evaluation of dot-to-dot exchange-bias variability, which becomes particularly large in the regime of switching via multidomain state formation. This variability issue is of particular importance in the context of MRAM development and of magnetoresistive heads for hard-disk drives [ABSTRACT FROM AUTHOR]

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, Hret, which acts against the applied field, H. We show that Hret 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. [ABSTRACT FROM AUTHOR]

For ferromagnetic (F)/antiferromagnetic (AF) nanodots contributions of AF spins to exchange bias is discussed. The relative weights of AF entities located at the dot edges, at the F/AF interface and in the AF grains were obtained by comparing the blocking temperature distribution of an array of nanodots with that of corresponding continuous film. Due to grain cutting, the grain size distribution is altered. We show here that the dot edges constitute additional locations for the formation of spin-glasslike AF regions at the F/AF interface. The result of patterning is thus twofold and weakens the dot ability to resist thermally activated magnetization reversal. [ABSTRACT FROM AUTHOR]

The magnetic properties of perpendicular exchange biased ferromagnetic (FM)/antiferromagnetic (AFM) [Pt/Co]n/IrMn systems were investigated by a new set-up combining element-selective soft x-ray holography and spectroscopy measurements. The holography experiments allow imaging the magnetization reversal of an exchange biased FM layer with an equivalent Co thickness below 5 nm in real space and in external magnetic fields, and provide direct evidence of its asymmetric nature. From the spectroscopy analysis, we have quantified the unpinned (pinned) uncompensated AFM moments, providing direct evidence of its parallel (antiparallel) alignment with respect to the FM moments. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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≤1.5×1012 A/m2), the DW motion obeys a creep law. At higher current density (j=1.8×1012 A/m2), zero-field average DW velocities up to 130±10 m/s were recorded. [ABSTRACT FROM AUTHOR]

In this paper, we describe a new media for heat assisted magnetic recording at ultrahigh density. Thermal simulations were performed to optimize this media. It consists in a patterned porous silicon substrate on which magnetic multilayers are deposited by magnetron sputtering. Magnetic properties of these multilayers are compared to those of layers deposited on regular silicon substrate. Despite the very particular structure of porous silicon surface, no big differences are observed and magnetic properties of the multilayers are conserved. Writing tests will be performed on these media with heating tips. [ABSTRACT FROM AUTHOR]

Only a very few experimental techniques can address the microscopic magnetization reversal behavior of the different magnetic layers in a multilayered system with element selectivity. We present an element-selective study of ferromagnetic (FM) [Co/Pt]n multilayers with perpendicular anisotropy exchange-coupled to antiferromagnetic (AFM) FeMn and IrMn films performed with a new experimental set-up developed for both soft x-ray spectroscopy and holography imaging purposes. The spectroscopy analysis allows the quantification of the unpinned (pinned) uncompensated AFM moments, providing direct evidence of its parallel (antiparallel) alignment with respect to the FM moments. The holography experiments give a direct view of both FM and uncompensated AFM magnetic structures, showing that they replicate to each other during magnetization reversal. Remarkably, we show magnetic images for effective thicknesses as small as one monolayer. Our results provide new microscopic insights into the exchange coupling phenomena and explore the sensitivity limits of these techniques. Future trends are also discussed. [ABSTRACT FROM AUTHOR]

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 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 domain wall nucleation and stopping DW propagation at the edge of the electrode. [ABSTRACT FROM AUTHOR]

A correction to the article "High domain wall velocities induced by current in ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy" that was published online in the October 29, 2009 issue is presented.