We present a magnetic domain-imaging study by x-ray magnetic circular dichroism photoelectron emission microscopy on a Co/Fe 75 Gd 25 bilayer under exposure to single focused ultrashort (100 fs) infrared laser pulses. Magnetic domain walls experience a force in the intensity gradient of the laser pulses away from the center of the pulse, which can be used to steer domain walls to move in a certain direction. Maximum domain-wall displacements after individual laser pulses close to 1 µm in zero external field are observed. Quantitative estimates show that electronic spin currents from the spin-dependent Seebeck effect are not strong enough to explain the effect, which we thus attribute to the torque exerted by magnons from the spin Seebeck effect that are reflected at the domain wall.

International audienceWe present a microscopic investigation of how the magnetic domain structure in ultrathin films changes after direct excitation by single ultrashort laser pulses. Using photoelectron emission microscopy in combination with x-ray magnetic circular dichroism in the resonant absorption of soft x rays, we find that individual laser pulses of ≈60 fs duration and a central wavelength of 800 nm lead to clear changes in the domain structure of a Co layer of three atomic monolayers thickness in an epitaxial Co/Cu/Ni trilayer on a Cu(001) single-crystal substrate. A relatively small enhancement of the sample base temperature by 40 K is sufficient to lower the threshold of laser fluence for domain wall motion by about a factor of two. Pump-probe measurements with a laser fluence just below this threshold indicate that the laser-induced demagnetization of the sample is far from complete in these experiments. Although the domain wall motion appears similar to thermal domain wall fluctuations, quantitatively it cannot be explained by pure thermal activation of domain wall motion by the transient rise of sample temperature after the laser pulse, but it is likely to be triggered by a laser-induced depinning of domain walls

We investigated the magnetic interlayer coupling between two ferromagnetic (FM) Ni layers through an antiferromagnetic (AFM) Ni 25 Mn 75 layer and the influence of this coupling on the exchange bias phenomenon. The interlayer coupling energy of an epitaxial trilayer of 14 atomic monolayers (ML) Ni/45 ML Ni 25 Mn 75 /16 ML Ni on Cu 3 Au(001) was extracted from minor-loop magnetization measurements using in-situ magneto-optical Kerr effect. The interlayer coupling changes from ferromagnetic to antiferromagnetic when the temperature is increased above 300 K. This sign change is interpreted as the result of the competition between an antiparallel Ruderman-Kittel-Kasuya-Yosida (RKKY)-type interlayer coupling, which dominates at high temperature, and a stronger direct exchange coupling across the AFM layer, which is present only below the Néel temperature of the AFM layer. V

Research on ultrathin magnetic layers and layered materials has reached an enormous impact, both scientifically and economically, with respect to applications in magnetic data storage technology, as sensors, or for future electronics utilizing the spin rather than the charge of electrons, the so-called "spintronics". [1][2][3][4] The physical size of a bit of information in magnetic data storage is already in the nanometer regime and is still shrinking, following the everincreasing demand for higher recording densities. Very soon the dimension of the recording bit will reach the sub-10 nm range. This poses formidable challenges to the read sensors. One ingredient of hard disk read sensors are magnetic layered systems in which ferromagnetic (FM) and antiferromagnetic (AFM) materials are in contact. [5] They show the exchange bias (EB) effect, which has received increased attention during the past decades. [6][7][8][9][10][11] It manifests itself in a shift of the magnetic hysteresis loop of the FM layer along the field axis. [12] Although reported first in 1956, [13] it was only in the mid-1990s that it shifted into the center of interest, triggered by applications of FM/AFM heterostructures for tailoring the magnetic properties of magnetoresistive devices. The past years have seen significant advances toward an explanation of the effect, however, a fundamental microscopic picture of the origin of the unidirectional magnetic anisotropy present in the EB effect is still missing.The occurrence of EB requires two basic ingredients: a magnetic interaction between FM and AFM spins at the interface, and a pinning of magnetic moments against the reversal of the FM-layer magnetization by the external magnetic field inside the AFM layer. As in AFM materials the direction of the spins varies on the length scale of single atomic distances, a thorough characterization of the atomic structure of the films and their interface is mandatory for fundamental investigations into the effect. In the commonly used polycrystalline systems prepared by sputtering techniques this is naturally not the case. A promising approach is the investigation of single-crystalline systems. [14][15][16][17][18][19] In such systems, it is shown, for example, that the magnetic coupling between AFM and FM layers is due to