X-ray photoemission electron microscopy (X-PEEM) is a powerful imaging technique that can be used to perform element selective magnetic domain imaging on heterogeneous samples with different magnetic layers, like spin valves and tunnel junctions. We have performed nanosecond time-resolved X-PEEM measurements, on the permalloy layer of a Ni80Fe20 (5 nm)/Cu (10 nm)/Co (5 nm) trilayer deposited on Si(111). We used the pump-probe mode, synchronizing a magnetic pulse from a microcoil with the x-ray photon bunches delivered by the BESSY synchrotron in single bunch mode. Images could be acquired during and after the 20 ns long and 80 Oe high field pulses. The nucleation and subsequent growth of reversed domains in the permalloy could be observed, demonstrating the feasibility of element selective and time-resolved domain imaging using X-PEEM

The magnetic coupling between epitaxial single-crystalline Co and FeMn layers on Cu(001) was investigated by element-resolved magnetic circular dichroism domain imaging using a photoelectron emission microscope. As-grown Co domain patterns reveal the presence of many small domains in the antiferromagnet. The coupling of the Co layer is found to be along <100> crystallographic directions. This is discussed in terms of a 45degrees coupling due to frustrations at topological 90degrees domains in the FeMn layer. Coercivity oscillations as a function of FeMn thickness with atomic monolayer period support the importance of such step-induced domains in the coupling

Using photoemission electron microscopy in combination with x-ray magnetic circular dichroism, element selective magnetic domain images have been obtained from single-crystalline Co/FeMn and FeMn/Co bilayers epitaxially grown on a Cu(001) single crystal. The contact with ferromagnetic Co leads to the observation of a net magnetic moment in Fe and Mn, independently of the paramagnetic or antiferromagnetic state of the FeMn thin films. Only a small fraction of this moment might mediate the magnetic interaction at the interface, and thus be responsible for the exchange bias effect

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We have studied the magnetization reversal dynamics of spin valves and magnetic tunnel junctions deposited on step bunched silicon substrates with a strong topological modulation. Our measurements show that the magnetization reversal is dominated by domain wall propagation at low field sweep rates and nucleation processes at high sweep rates. The magnetostatic orange peel coupling present in quasi-static conditions between the magnetic layers disappears when switching by nucleation becomes dominant. Micromagnetic simulations show that this phenomenon can be explained taking into account the modulated topology of the substrate

We have obtained microscopic evidence of the influence of domain wall stray fields on the nanosecond magnetization switching in magnetic trilayer systems. The nucleation barrier initiating the magnetic switching of the soft magnetic Fe 20 Ni 80 layer in magnetic tunnel junctionlike FeNi/ Al 2 O 3 / Co trilayers is considerably lowered by stray fields generated by domain walls present in the hard magnetic Co layer. This internal bias field can significantly increase the local switching speed of the soft layer. The effect is made visible using nanosecond time-and layer-resolved magnetic domain imaging and confirmed by micromagnetic simulations. DOI: 10.1103/PhysRevB.72.220402 PACS number͑s͒: 75.60.Jk, 75.60.Ch, 75.70.Ϫi, 85.70.Kh The active part of devices such as spin valves and magnetic tunnel junctions, used in magnetic random access memories ͑MRAM͒, consists of an ultrathin soft ferromagnetic ͑FM͒ layer and a harder ferromagnetic layer separated by a nonmagnetic ͑NM͒ spacer layer. These devices rely on the fast switching of the magnetization of the soft layer for reading or writing separate bits of information. Micromagnetic interactions have a strong influence on this switching. Demagnetizing effects and stray fields at the edges of nanosized magnetic structures can influence the magnetic configuration and the magnetization reversal of the soft magnetic layer, but interface roughness can also play a role and induce a magnetostatic coupling with the underlying hard magnetic layer. Much larger, but more localized magnetostatic effects exist when a domain wall is present in the hard magnetic layer.1,2 Direct evidence of the influence of domain wall stray fields in one layer on the static domain configuration of another layer has been obtained by Kuch et al. 3 on Co/ Cu/ Ni trilayers using x-ray photoelectron emission microscopy ͑X-PEEM͒. Schäfer et al. 4,5 have used Kerr microscopy to show the effect of stray fields of Bloch domain walls in an Fe whisker on the magnetization of a thin Fe film through a MgO spacer. Similar effects were recently also observed in systems with perpendicular magnetization.6 Thomas et al. 7 have observed that repeated motion of domain walls in the soft magnetic layer of a FM/ NM/ FM trilayer can demagnetize the hard magnetic layer, even if the field used for the reversal is much smaller than the coercive field of the hard layer. In thin films with in-plane uniaxial anisotropy the static coercivity is usually determined by the field needed for domain nucleation. In FM/ NM/ FM trilayers, the stray field of a domain wall in the hard magnetic layer can locally decrease this quasistatic nucleation field in the soft magnetic layer.1 In this paper we show a direct, real-time observation of this effect in Fe 20 Ni 80 /Al 2 O 3 / Co trilayers. In order to do so, we took advantage of the element selectivity of X-PEEM combined with x-ray magnetic circular dichroism ͑XMCD-PEEM͒. Our micromagnetic simulations show that the stray field of domain walls in the Co layer locally tilts the magneti...

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.

The magnetization reversal dynamics of an Fe20Ni80∕Cu∕Co spin valve is investigated on the nanosecond time scale by magnetic microscopy with time and layer resolution. It is found that the speed by which micron-sized magnetic domains in the magnetically soft Fe20Ni80 layer are expanded by external field pulses exhibits a dependence on the change in domain-wall length, and on the coupling to the local magnetization direction of the Co layer.