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Author(s): Y. Acremann [1]; M. Buess [1]; C. H. Back [1]; M. Dumm [2]; G. Bayreuther [2]; D. Pescia (corresponding author) [1] For the development of future magnetic data storage [...]

A study was conducted to investigate the grazing incidence nuclear multilayer diffraction of synchrotron radiation resulting from a periodic stack of alternating 56Fe and 57Fe layers. The purity structure and lateral homogeneity of the isotopic multilayer film was determined by magnetometry. Results indicated the effectiveness of molecular beam epitaxy in generating narrow band monochromators and synthetic isotropicaly periodic multilayers supporting no sign of layer interdiffusion.

Superconducting quantum interference device magnetometry is used for examining the magnetization reversal and temperature dependence of the spontaneous magnetization in nanomagnets fabricated from ultrathin, epitaxial Fe(001) films. The decline in dot diameter by a factor of 4 increases the spin wave parameter B resulting in a 25 percent decrease in the magnetization at room temperature.

Magneto-optic Kerr effect was used for examining the magnetic properties of the epitaxial Fe(sub 1-x)Co(sub x) alloy films grown on GaAs(001). Ferromagnetic order at room temperature for thickness above 4 ML was observed.

The connection between the onset of ferromagnetism with an onset of magnetic anisotropy is examined. Ferromagnetic long-range order and uniaxial magnetic anisotropy appear for T >0 above a critical thickness of 2.5 ML suggesting the strong correlation between the onset of ferromagnetism and of magnetic anisotropy for Fe on GaAs(001).

The relation between the strong uniaxial magnetic anisotropy of Fe/GaAs(001) with the specific GaAs(001) surface reconstruction is examined. The easy axis of the uniaxial anisotropy is found along [110] in Fe(001) films grown by molecular-beam epitaxy on Ga-rich GaAs(001) surfaces at room temperature.

The magnetic properties of nanopatterned epitaxial iron films on GaAs are discussed. A strong dependence of their remanent state of the Fe(110) elements was observed on the magnetic history whereas Fe(001) elements displayed the same remanent magnetization pattern.

It has been possible to use magnetic transmission x-ray microscopy to image magnetic domains with a lateral resolution down to 25 nm. The first images taken with thin Fe layers give an insight into the switching behaviour in complete hysteresis loops.

Research into the magnetization reversal of an array of 1 micro-m squared FeGd dots is presented. It was established that the dots switch in a defined and reproducible order. However, there is a large variation from dot to dot in the field where nucleation occurs.

It has been possible to grow expitaxial Fe films ranging in thickness from 4 to 64 monolayers by molecular beam epitaxy on GaAs(110) at room temperature. It was found that, with decreasing temperature, the magnetic anisotropy in the films appeared to become more bulk-like.

It has been possible to grow ultrathin Fe films epitaxially at room temperature on GaAs(001) with either predominant (4x2) or (2x6) surface reconstruction. The onset of ferromagnetism was shown at a nominal Fe coverage of 2.5 monolayers.

Research into electric transport through magnetic tunnel junctions is presented. It was found that, at room temperature, the spin-independent hopping conductance of the junctions was less than 10% of the total conductance. With regard to the magnetic properties, a ferromagnetic orange-peel coupling relating to a field of around 4 Oe was found at 15 K.

Epitaxial Fe(sub 34)Co(sub 66) films in a thickness range from 3 to 100 monolayers (MLs) were grown by molecular beam epitaxy on GaAs(100) at room temperature. The growth was characterized by reflection high energy electron diffraction and x-ray diffraction.

A study was conducted to analyze in-plane fourfold and uniaxial magnetic anisotropies in iron films. The films were grown epitaxially on vicinal Ag(001) and Au(001) surfaces prepared by molecular beam epitaxy on miscut GaAs(001) substrates. the residual pressure in the chamber remained below 5x10(super -10) mbar during film deposition. Experimental results indicated that the orientation of the uniaxial easy axis correlated with the iron thickness.

X-ray magnetic circular dichroism (X-MCD) combined with anomalous small angle x-ray scattering (ASAXS) enables size distributions and correlations lengths in the nanometer range of magnetic precipitates in granular systems to be determined. Standard ASAXS measurements on an amorphous GdFe system, taken at the Fe K edge, gives information about the electronic structure. Magnetic scattering curves were obtained at the corresponding Gd L(sub3,2) edges.

A two-coercivity model and remanence measurements were used to study the reversal mechanisms in Tb/Fe multilayers. The model delineated the hysteresis form as a function of bilayer numbers. Remanence measurements elucidated energy barrier distribution for two coercive processes.

Time-resolved x-ray magnetic circular dichroism is used for examining ferromagnetically coupled CoFe/Ru/NiFe bilayers. The magnetization dynamics is driven by a continuous wave excitation and the processional motion of the individual layers is detected separately by tuning the x-ray photon energy to the [L.sub.3] absorption edge of either Ni or Ce.

The magnetization dynamics of each layer of interlayer exchange coupled [Ni.sub.81][Fe.sub.19]/Ru(t)/[Co.sub.90][Fe.sub.10] films is examined by using time resolved x-ray magnetic circular dichroism after pulsed excitation. Two different stack geometries are used for showing how to change from in-phase to antiphase excursion in a bilayer.

Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR) and vector network analyzer FMR (VNA-FMR) are used for studying of interlayer exchange coupled Si/Ta/NiFe/Ru/NiFe/Ta films of variable Ru thickness. The intersection of optical and acoustical modes is observed with VNA-FMR and the PIMM measurements have showed a double peak at the intersection field.

Spin-wave excitations in ultrathin epitaxial FeCo(001) films on Au(001) with in-plane magnetic anisotropies drastically reduced in comparison to pure Fe(001) films. The results reveal that the effect of a weak in-plane anisotropy is overcompensated by the enhanced exchange interaction.

Epitaxial Fe(001) films with thickness less than 20 monolayers were grown on epitaixial Au(001) surfaces by molecular beam epitaxy. The magnetic behavior of Fe films on GaAs(001) is governed by a superposition of a dominating uniaxial and a fourfold anisotropy component.

A pulsed inductive microwave magnetometer is used to examine magnetization dynamics. The thin film sample is brought into close proximity to the coplanar waveguide that allows for simple changing of samples.

Presents information on a study which observed grazing incidence nuclear multilayer diffraction of synchroton radiation from a periodic stack of alternating iron 56 and 57 layers. Methodology of the study; Results and discussion on the study; Conclusions.

The temperature dependence of magnetization in ultrathin epitaxial Fe films and the effect of nanopatterning is presented. Smaller dots and magnetic microscopy with picosecond time resolution in combination with spin wave calculations and numerical simulations will be required in the future.

The influence of the transition on the domain configuration in the nanomagnets made of bcc Fe(001) films is presented. The simulation resulted not only in single domain but also in two-domain states with a vortex at the center of the wall similar to the configuration found for 35 nm thick epitaxial Fe(110) disks.

High speed signal transmission with magneto-couplers is discussed. Our measurements show that by choosing an appropriate configuration of internal and external magnetic fields and preferred directions present magneto-couplers are suitable for high speed signal transmission.

Investigates the hysteresis properties of ultrathin ferromagnetic films. Characteristics of the film at low temperature; Discussion on the role of roughness in the hysteresis properties of ferromagnetic ultrathin films; Model of wall motion which provides an explanation of the overall observations.

The observation of undulation instabilities in nanostructured strips of a ferromagnetic Fe/Gd multilayer by magnetic transmission x-ray microscopy (MTXM) is presented. The novel technique of magnetic transmission x-ray microscopy, which is based on the x-ray magnetic circular dichroism, is used for imaging.

The magnetization dynamics of each layer of interlayer exchange coupled Ni81Fe19/Ru(t)/Co90Fe10 films was investigated by time resolved x-ray magnetic circular dichroism (TR-XMCD) after pulsed excitation. The coupling was changed from ferromagnetic to antiferromagnetic by variation of the Ru thickness t. The precessional motion of the individual layers was detected separately by measuring the XMCD signal at the L3 absorption edge of either nickel or cobalt. From the observation of two frequency components in the precession of both layers in samples with negligible interlayer exchange coupling, the presence of a different coupling mechanism was concluded. Using two different sample geometries, the influence of antiphase and in-phase excitation on the triggered dynamics was studied. [ABSTRACT FROM AUTHOR]

Pulsed inductive microwave magnetometer (PIMM), conventional ferromagnetic resonance (FMR), and vector network analyzer FMR (VNA-FMR), as well as quasistatic methods such as a magneto-optic Kerr effect magnetometer and a vibrating sample magnetometer, have been used for complementary studies of interlayer exchange coupled Si/Ta/NiFe(30 nm)/Ru(t)/NiFe(30 nm)/Ta films of variable Ru thickness t. The coupling constants were determined from the measured magnetization curves by fitting them to simulated ones. The dynamics measurements revealed two spin wave modes, which could be identified as optical and acoustical ones. The optical mode changes significantly with the coupling, whereas the slight change of the acoustical mode is due to different relative orientations of the layer magnetizations. Numerical simulations helped to identify optical and acoustical modes. The intensity of these two modes changes with the bias field and coupling. Using VNA-FMR the optical mode could be observed up to higher bias fields than with the PIMM at small excitation angles. While varying the pulse field up to 150 Oe using the PIMM, the intensity ratio of optical and acoustical modes changed and additional modes occurred. [ABSTRACT FROM AUTHOR]