Neutron scattering has been the scattering technique of choice for the analysis of magnetic structures and their dynamics for many decades. The advent of magnetic thin film systems has posed new challenges since such samples have inherently small scattering volumes. By way of examples, recent progress in the application of neutron scattering for the study of both magnetic structure and dynamics in magnetic thin film systems will be presented. First, a combined high angle neutron scattering and polarized neutron reflectivity investigation of the magnetic order of Cr and its influence on the exchange coupling between the Fe layers in Fe/Cr superlattices is discussed. It is shown that in the whole thickness range up to 3000 Å, the magnetic structure is governed by frustration effects at the Fe/Cr interfaces. Second, it is demonstrated that it is now possible to investigate the dynamic properties of magnetic thin films with neutron scattering. Unlike, e.g., Brillouin light scattering, inelastic neutron scattering provides access to large portions of the Brillouin zone. First results on spin wave excitations in a Dy/Y superlattice are presented.

We report about synchrotron and neutron-scattering studies investigating incommensurate spin-density waves (I-SDW's) in epitaxially grown thin Cr(001) films, including surface and interface effects. These studies show that thin ferromagnetic cap layers of Fe, Ni, and Co with a thickness of only 2-3 nm have a strong effect on the propagation and orientation of the I-SDW's in Cr. For thick Cr films there exist essentially only transverse I-SDW's propagating parallel to the:film plane with the spins oriented normal to the planet and at right angles to the in-plane magnetization of the ferromagnetic cap layers. With decreasing Cr thickness a different transverse I-SDW grows at the expense of the in-plane ones, now propagating normal to the plane and with spins parallel or antiparallel to the film magnetization. At a Cr thickness of about 250 Angstrom, the transverse out-of-plane I-SDW completely dominates the phase diagram of Cr. All other domains are suppressed and a spin-flip transition does not occur above 10 K in strong contrast to bulk. For in-plane propagation of the T-SDW we find a coexisting commensurate spin-density wave (C-SDW) which vanishes during the reorientation to. out-of-plane propagation with Cr thickness. Finally,for Cr thicknesses well below the period of the I-SDW, the Cr can only order as a C-SDW. The behavior of the SDW's in thin Cr films with ferromagnetic cap layers can be understood in terms of competing interactions at the rough interfaces inducing frustration and by finite-size and strain effects. We have also investigated the effect of Cu and Pd cap layers on the SDW. The Cu cover is similar to a Cr/vacuum interface, whereas the effect of the Pd cover is intermediate between the ferromagnetic layers and Cu. [S0163-1829(99)11513-3].

The damping of magnetic excitations is an essential point of interest in research and technical application of thin magnetic films. Therefore, electronic and structural influences of adjacent Cr-layer on the static and dynamic damping contribution in thin Fe-films were studied by Ferromagnetic Resonance (FMR). Not only for its spin-dependent transport properties [I] but also for fundamental aspects of the interaction at the interface between ferromagnetically (fm) and an antiferromagnetically (afm) ordered structures the system Fe/Cr is of importance [2].

Investigations on the magnetic behavior of expitaxially grown Fe films on Cr were performed by ferromagnetic resonance (FMR) and by SQUID DC-magnetometry. The magnetic Fe parameters show a significant deviation from the expected temperature dependence which is attributed to a change of the interface coupling between Fe and Cr. The observed anomalies are related to the spin–flip in Cr where the orientation of the magnetic moments flips from out-of-plane to in-plane alignment. The spin–flip transition temperature depends on the Cr thickness. The spin–flip is suppressed for Cr thicknesses comparable to the wavelength of the sinusoidal modulated antiferromagnetic groundstate. In addition, the influence of the interface conditions on the formation of standing spin waves in Fe on Cr has been studied.

We have investigated the magnetic structure of thin [001] oriented Cr films using neutron and X-ray diffraction experiments to measure their spin density waves and the strain waves, respectively. For epitaxial Cr films with thicknesses between 1000 and 4000Å grown on Nb films on sapphire substrates, we provide phase diagrams including incommensurate transverse and longitudinal spin-density waves (SDW) as well as commensurate antiferromagnetic spin structures. The results show that for Cr(001) on Nb a single domain SDW prevails with a wave vector Q perpendicular to the surface. At low temperatures the SDW is longitudinal and becomes mostly transverse between 150 and 250K, higher than in bulk Cr where the spin–flip transition occurs at 123K. Furthermore, the magnitude of Q is increased as compared to bulk Cr. These effects decrease with increasing film thickness. With neutron scattering we have also observed a commensurate antiferromagnetic phase with spins pointing out of the plane. The commensurate phase occurs at a temperature between 250 and 305K and persists up to at least 340K, far above the bulk Néel temperature of 311K for the incommensurate phase.

The spin density wave (SDW) magnetism of thin epitaxial Cr films has recently become the focus of interest because of its mediating role in exchange coupled superlattices. While the incommensurate SDW and the Néel temperature,, are well established for bulk Cr, the question arises of how these properties are altered in thin films and superlattices with ferromagnetic boundary layers. We review here recent synchrotron and neutron scattering experiments to probe the commensurate and incommensurate SDWs in epitaxial Cr(100) layers and the phase diagrams which result from these measurements as a function of film thickness and temperature. Finally, we link the antiferromagnetic spin structure of Cr to the Fe layer magnetization vectors in exchange coupledsuperlattices, which provides a deeper insight for the cause of non-collinear magnetic ordering in these artificial superlattices.

For thin epitaxial Cr(001) films capped with a ferromagnetic Fe layer a transverse spin density wave (SDW) is expected which propagates in the out-of-plane direction with the Cr spins aligned parallel to the film plane in the direction of the Fe magnetization vector. Synchrotron and neutron scattering experiments show, however, that the SDW wave propagates parallel to the film plane with spins oriented out-of-plane. In addition, a commensurate antiferromagnetic phase is found. The re-orientation of the SDW is caused by a frustrated Fe–Cr exchange coupling introduced by monoatomic steps at the Fe–Cr interface. Complete re-orientation takes place over some distance close to the interface reducing severely the coherence length of the SDW structure. With the surface scattering method we have measured the coherence length of the SDW as a function of depth. Furthermore, we have investigated the role of the commensurate antiferromagnetic phase near the Fe–Cr interface. We find no scattering from a commensurate order, implying a layering of the two phases with the incommensurate phase on top.

To study the interface interactions between ferromagnetic ordered Pe and antiferromagnetic ordered Cr we used Ferromagnetic Resonance (FMR) Spectroscopy and SQUID magnetometry, For a defined Cr thickness range the magnetic parameters of the Fe films show an anomalous temperature behavior which can be related to a change of the intrinsic spin structure of the chromium, the so-called spin-Dip transition. The transition temperature decreases continuously with decreasing Cr thickness, ceasing in a suppression of the transition for Cr films below 60 Angstrom.

Reflection high-energy electron diffraction (RHEED) intensity studies were performed during the growth of thin Fe layers on vicinal Cr(001)/Nb(001)/Al2O3(1 (1) over bar 02) substrates. The results are compared with those of recent molecular-beam epitaxy (MBE) growth models. General agreement is found as concerns the linear relationship between the logarithm of the number of RHEED oscillations and the inverse growth temperature. In agreement with theory the RHEED oscillation damping time is found to depend algebraically on the growth rate. However, contrary to expectations, the RHEED oscillations vanish faster at higher growth temperatures and lower growth rates. This behavior can be explained by a change in the growth mode from layer-by-layer to step flow. Numerical simulations in which step bunch melting during the Fe growth on the Cr buffer is assumed reproduce well the present experimental results. [S0163-1829(98)02708-8].

Proximity effects of 20 Angstrom Fe layers on the spin density waves (SDWs) in epitaxial Cr(001) films are revealed by neutron scattering. Unlike in bulk Cr we observe a SDW with its wave vector Q pointing along only one (100) direction which depends dramatically on the film thickness t(Cr). For t(Cr) < 250 Angstrom the SDW propagates out of plane with the spins in the film plane. For t(Cr) > 1000 Angstrom the SDW propagates in the film plane with the spins out of plane perpendicular to the in-plane Fe moments. This reorientation transition is explained by frustration effects in the antiferromagnetic interaction between Fe and Cr across the Fe/Cr interface due to steps at the interface.

We demonstrate how the noncollinear exchange coupling between the Fe layers in Fe/Cr(001) superlattices is caused by a frustrated spiral modulation of the Cr moments not observed in bulk. The noncollinear coupling vanishes above the Neel temperature of this commensurate antiferromagnetic Cr order. This clarifies the essential contribution of Cr ordering to the coupling in the regime of smallest thicknesses where no incommensurate Cr spin density wave can form. For larger Cr thicknesses we observe a predicted incommensurate to commensurate transition with temperature.

We have investigated proximity effects of Fe layers on the spin density waves (SDW) and the concomitant charge density waves or strain waves in thin epitaxial Cr[001] films using synchrotron and neutron scattering. Unlike in bulk Cr we observe a strong anisotropic occupation of the three possible SDWs with their wave vectors Q pointing along the {001} directions. In a pure 3000 Å thick Cr[001] film, the SDW exhibits an almost complete out-of-plane orientation, whereas in a Cr film of the same thickness capped by a 20 Å Fe layer the SDW becomes completely reoriented with Q now propagating in the plane. This SDW is preserved over the entire temperature range from 10 K up to the Néel temperature of about 311 K.

We have investigated proximity effects of Fe layers on the spin density waves (SDW) in thin epitaxial Cr[0 0 1] films with neutron scattering. Unlike in bulk Cr we observe a strong anisotropic occupation of the three possible SDWs. In pure Cr[0 0 1] films the SDWs exhibit an almost complete out-of-plane propagation with spins parallel to Q. With only 20 A Fe on top of these Cr films, the SDW becomes completely re-oriented with Q now propagating in the plane but the Cr-spins still point out of the plane. This implies that the Fe and Cr moments are ooriented perpendicular to each other.

Ferromagnetic (FMR) and nuclear magnetic (NMR) resonance studies of MBE grown Co/Cu(111) superlattices are presented. With FMR, the sixfold magnetocrystalline in-plane anisotropy, K4, is determined as a function of temperature, T. It is shown that K4 differs from the bulk hcp value not only quantitatively (i.e. in magnitude) but also qualitatively in the sense that its temperature dependence is significantly weaker. Both features are explained by the dominating fcc stacking proved by our 59Co NMR and X-ray investigations.

We present the observation of charge density waves and strain waves in thin epitaxial Cr(001) films by means of scattering with synchrotron radiation. The Cr films were grown by molecular beam epitaxial techniques on MgO(001) substrates and on Al2O3 (11¯02) substrates with a Nb(001) buffer layer. The ratio between the amplitudes of both modulations can be derived from the measured intensities. From the data a substrate induced change of this ratio and of the modulation wavelength as compared to the bulk value can be infered.

It is explained why the analysis our FMR data from Co/Cu(111) single layers and superlattices is appropriate. This is supported by the results of structural investigations.

NMR using the 59Co nucleus has been measured for a series of Cu/Co/Cu(111) trilayers grown by MBE with Co thicknesses ranging from 25 to 178 Å. The Co layer retains the Cu fcc structure up to a thickness of ∼ 60 Å at which point the hcp structure is favoured. This structural transition is not identical for each sample suggesting that the point at which the transition occurs depends on the exact growth conditions including the thickness of the Cu underlayer. Our results suggest that for very thin (15 Å) Cu underlayers the transition to hcp occurs at thicknesses less than 60 Å.