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The long-range magnetic structure in Co/Pt multilayers magnetically patterned by ion irradiation is observed by off-specular polarized neutron reflectivity. While both specular and off-specular measurements indicate the formation of an artificial domain structure when the sample is in its remanent state, resonant peaks seen in the diffuse scatter reveal long-range magnetic ordering with periodicity in agreement with the design value. These peaks are completely suppressed when the sample is saturated in plane, confirming their origin in the magnetic patterning of the multilayer. [ABSTRACT FROM AUTHOR]

The observed magnetotransport properties of magnetically coupled multilayers depends not only on the nature of the magnetic coupling but also the magnetic domain correlations and disorder. Neutron scattering gives access to the magnetic coupling through the specular reflectivity and the domain correlations through the diffuse scattering. Sputtered multilayers of Co/Cu and Co/Ru have been investigated as a function of the applied magnetic field. A simple domain model relates the observed scattering to the domain correlation length and the magnetic disorder. In both systems highly vertically correlated magnetic domains are observed with in-plane correlation lengths, at remanence, of 1.5 and 7 μm for the Cu and Ru systems, respectively. In both systems the Co domains order antiferromagnetically across the nonmagnetic spacer. The remanent vertically correlated state is recovered after saturating the sample. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In the majority of magnetic systems the surface is required to order at the same temperature as the bulk. In the present Letter, we report a distinct and unexpected surface magnetic phase transition at a lower temperature than the Néel temperature. Employing grazing incidence x-ray resonant magnetic scattering, we have observed the near-surface behavior of uranium dioxide. UO2 is a noncollinear, triple-q, antiferromagnet with the U ions on a face-centered cubic lattice. Theoretical investigations establish that at the surface the energy increase—due to the lost bonds—is reduced when the spins near the surface rotate, gradually losing their component normal to the surface. At the surface the lowest-energy spin configuration has a double-q (planar) structure. With increasing temperature, thermal fluctuations saturate the in-plane crystal field anisotropy at the surface, leading to soft excitations that have ferromagnetic XY character and are decoupled from the bulk. The structure factor of a finite two-dimensional XY model fits the experimental data well for several orders of magnitude of the scattered intensity. Our results support a distinct magnetic transition at the surface in the Kosterlitz-Thouless universality class. [ABSTRACT FROM AUTHOR]

Abstract: OffSpec has been purposely built as a low background, polarised neutron reflectometer with spin-echo for Larmor labeling. The instrument received first neutrons in December 2008 and five of the intended seven modes of operation have now been tested and operated with peer reviewed user experiments. The technical performance of the instrument will be reviewed in each of the modes and future scientific possibilities discussed. Particular attention will be paid to results from spin-echo SANS (SESANS) and spin-echo resolved grazing incidence scattering (SERGIS), where the largest number of measurements have been performed. [Copyright &y& Elsevier]

Collective behaviors in which the magnetic response depends not only on the individual constituents but also on their interactions are an area of active research. We have produced a paradigmatic system where DC magnetron sputtered FexAg100-x (x=15, 35) nanogranular films exhibit a crossover between a superspin glass (SSG) state and a superferromagnetism (SFM), where direct exchange interactions overcome the frustration. The systems have been studied by non-linear susceptibility (NLS) and small angle neutron scattering (SANS). The NLS measurements were carried out between 2 and 300K, in the absence of a biasing magnetic field, with frequencies spanning two decades. These measurements shed light on the complex nature of the interactions and the intricate relationship between direct exchange and long range magnetic interactions. The use of SANS allows us to estimate qualitatively the lengthscale of the magnetic correlations, and therefore identify a clear difference between the collective "supermagnetic" states (i.e., SSG and SFM) while establishing links between the structure and the magnetic interactions. [ABSTRACT FROM AUTHOR]

The effect of ion irradiation on the proximity effect in YBa2Cu3O7−δ/La0.67Sr0.33MnO3 and YBa2Cu3O7−δ/SrTiO3/La0.67Sr0.33MnO3 heterostructures has been investigated using spin-polarized neutron reflectivity experiments. We demonstrate that the magnetization in the ferromagnetic (La0.67Sr0.33MnO3) layer at the interface is correlated with the suppression of the superconductivity in the YBa2Cu3O7−δ layer after irradiation, while the layer structure of the heterostructures remains intact. The evolution of the magnetization of the interfacial ferromagnetic layer studied as a function of temperature for both the irradiated heterostructures shows the absence of the proximity effect observed in the un-irradiated samples. The absence of a proximity effect is attributed to the suppression of the superconductivity, as seen in macroscopic magnetization measurements of the heterostructures after ion irradiation. [ABSTRACT FROM AUTHOR]

Spin-polarised neutron reflectometry has been used to investigate a magnetic exchange spring, formed in a (75 Å DyFe2/150 Å YFe2)×18 multilayer thin film. The existence of an exchange spring is found to enhance the level of neutron spin flipping during reflection, a strong indicator of the formation of transverse magnetic moments within the YFe2 layers. [Copyright &y& Elsevier]

Antiferromagnetic coupling between rare-earth (RE) and transition metals (TM) gives rise to various magnetic ground states in RE/TM heterostructures. Interface structure and morphology tend to play important roles in defining the magnetic properties of heterostructures of these materials. Using spin-dependent polarized neutron reflectivity (PNR), we found a distinct magnetic structure for RE/TM (Gd/Co) multilayers having different interface morphologies. Two Gd/Co multilayers, each consisting of eight bilayers of Gd and Co, were grown at different argon pressures to accomplish variation in the interface morphology. The Gd/Co multilayer, which is grown at a lower argon pressure, exhibits lower intermixing/interdiffusion at the interfaces and shows asymmetric magnetic hysteresis loops below the compensation temperature (Tcomp ∼ 140 K) and antisymmetric magnetoresistance at Tcomp. The other multilayer, grown at two different argon pressures for the top and bottom four bilayers, shows a double hysteresis loop with an exchange-bias-like shift to the field axis at temperatures above Tcomp (∼150 K). From PNR measurements across Tcomp, these behaviors were attributed to interface dependent magnetic helical structures. The PNR results indicate the formation of a twisted helical magnetic structure with planar 2π domain walls and the evolution of magnetic inhomogeneities below Tcomp. The interface dependent twisted helical magnetic structures and the development of highly correlated magnetic inhomogeneities may find applications in all-spin-based technologies. [ABSTRACT FROM AUTHOR]

We have investigated the magnetic properties of a Cu capped thin film of magnetite (Fe[SUB3]O[SUB4]) grown epitaxially on Pt(111). Conversion electron Mössbauer spectroscopy data show good agreement with those from bulk Fe[SUB3]O[SUB4], evidencing a good degree of structural order. The data point to in-plane ferrimagnetic alignment of the magnetic moment in the Fe[SUB3]O[SUB4] layer. Polarized neutron reflectivity (PNR) data determines the layer thinknesses to be 53±6 A˚ for the magnetite film and 106±5 A˚ for the Cu capping layer. The average magnetic moment determined by PNR for the Fe[SUB3]O[SUB4] layer is 2.8±0.3 μ[SUBB], smaller than the value of 4.1 μ[SUBB] for bulk Fe[SUB3]O[SUB4]. It is suggested that the reduced moment is in part a result of a reduced ordering temperature in the ultrathin film. [ABSTRACT FROM AUTHOR]

We describe measurements of the uniaxial magnetic anisotropy and spin-flop rotation of the Néel vector in antiferromagnetic CuMnAs thin films using neutron diffraction. The suppression of the magnetic (100) peak under magnetic fields is observed for films as thin as 20 nm, indicating that they undergo a spin-flop transition. Good agreement is found between neutron diffraction and electrical transport measurements of the spin-flop rotation in the same layer with similar shape and hysteresis of the obtained curves, while the neutron measurements provide a quantitative determination of the spin flop extending throughout the antiferromagnet layer. [ABSTRACT FROM AUTHOR]

Magnetic reversal of an artificial square ice pattern subject to a sequence of magnetic fields applied slightly off the diagonal axis is investigated via magnetic force microscopy of the remanent states that result. Sublattice independent reversal is observed via correlated incrementally pinned flip cascades along parallel dipolar chains, as evident from analysis of vertex populations and dipolar correlation functions. Weak dipolar interactions between adjacent chains favour antialignment and give rise to weak charge ordering of 'monopole' vertices during the reversal process. [ABSTRACT FROM AUTHOR]

The understanding of electronic behaviour in systems with reduced dimensionality and length scale is a central theme of contemporary condensed matter physics. The unique capabilities of neutron scattering make it an ideal method to study the atomic and molecular, chemical and magnetic structure of a wide class of materials. In this review we highlight recent studies where neutron techniques have been applied to emergent materials and look forward to the possibilities enabled by instrumentation on the ISIS Second Target Station. [Copyright &y& Elsevier]

We report on a study of ferromagnetic semiconductor (Ga,Mn)As/(Al,Ga,Mn)As bilayers using magnetometry and polarized neutron reflectivity (PNR). From depth-resolved characterization of the magnetic structure obtained by PNR, we concluded that the (Ga,Mn)As and (Al,Ga,Mn)As layers have in-plane and perpendicular-to-plane magnetic easy axes, respectively, with weak interlayer coupling. Therefore, the layer magnetizations align perpendicular to each other under low magnetic fields and parallel at high fields. [ABSTRACT FROM AUTHOR]

We report on x-ray and neutron scattering studies that reveal the structure of interfaces of C60 layers with adjacent transition metal layers, in this instance, Cu. Such interfaces produce room-temperature long-range spin order that is not described by conventional theories of metallic magnetism. We use a combination of hard x-ray reflectivity and neutron scattering to investigate the interfacial structure of two C60/Cu layered samples: a superlattice with multiple C60/Cu repeats and a simpler tri-layer structure. For both structures, we develop a consistent structural model for the two scattering techniques, which details the critical interfacial roughness between the layers. We find that while x-ray reflectivity provides a strong contrast between the C60 and Cu layers, the similar neutron scattering length density of the two materials severely reduces the neutron scattering contrast. Our results can be used to design material systems that permit studies of the magnetism of the C60/transition metal interfaces with spin-sensitive scattering probes such as polarized neutron reflectometry. [ABSTRACT FROM AUTHOR]

Using spin-polarized neutron reflectivity experiments, we demonstrate an unusual proximity behavior when a superconductor (SC) and a ferromagnet (FM) are coupled through an insulator (I) in YBa2Cu3O7−δ (SC)/SrTiO3 (I)/La0.67Sr0.33MnO3 (FM) heterostructures. We have observed an unexpected magnetic reversal confined to the interface region of the FM below the superconducting transition temperature. The magnetization of the interfacial FM layer at the I/FM interface was found to be aligned opposite to the magnetization of the rest of the FM layer. This result indicates that the Cooper pairs tunnel across the insulator, interact with the local magnetization in the interfacial region (extending ∼30 Å) of the FM, and then modify the magnetization at the interface. This unexpected magnetic behavior cannot be explained on the basis of the existing theoretical models. However, the length scale associated here clearly suggests the long-range proximity effect as a result of tunneling of Cooper pairs. The magnetic exchange field-effect across SC/I/FM interfaces driven by tunneling may serve as the basis for application in superconducting spintronic devices. [ABSTRACT FROM AUTHOR]

Using the newly emerged theory model of an electromagnetic proximity effect, we demonstrate that it provides a good description of our previously reported anomalous Meissner screening observed in thin film superconductor-ferromagnet proximity structures. Using the low energy muon spin rotation measurement technique, we further investigate this new theory by probing directly the flux screening in various superconductor-ferromagnet proximity structures. We examine its main characteristics and find in general good agreement between theory and experiment. Understanding and control of this new proximity effect is an important step forward toward a new generation of superconducting spintronic devices. [ABSTRACT FROM AUTHOR]

Inserting an antiferromagnetic layer of NiO between Pt and Y3Fe5O12 (YIG) changes the positive sign of the spin Hall magnetoresistance (SMR) in Pt/YIG to a negative sign at low temperature. Here, we use polarized neutron reflectometry to explore the coupling between NiO and YIG to understand the mechanism of the negative SMR. A weak uncompensated magnetic moment is observed in the NiO and the direction of this moment is perpendicular to YIG. Therefore, we infer that the spin axis of NiO is perpendicular to YIG. This result directly supports the explanation that the negative SMR results from the pure spin current reflected back by the NiO layer and the spin-flop coupling between NiO and YIG. [ABSTRACT FROM AUTHOR]

We report measurements on yttrium iron garnet (YIG) thin films grown on both gadolinium gallium garnet (GGG) and yttrium aluminum garnet (YAG) substrates, with and without thin Pt top layers. We provide three principal results: the observation of an interfacial region at the Pt/YIG interface, we place a limit on the induced magnetism of the Pt layer, and confirm the existence of an interfacial layer at the GGG/YIG interface. Polarized neutron reflectometry (PNR) was used to give depth dependence of both the structure and magnetism of these structures. We find that a thin film of YIG on GGG is best described by three distinct layers: an interfacial layer near the GGG, around 5 nm thick and nonmagnetic, a magnetic "bulk" phase, and a nonmagnetic and compositionally distinct thin layer near the surface. We theorize that the bottom layer, which is independent of the film thickness, is caused by Gd diffusion. The top layer is likely to be extremely important in inverse spin Hall effect measurements, and is most likely Y2O3 or very similar. Magnetic sensitivity in the PNR to any induced moment in the Pt is increased by the existence of the Y2O3 layer; any moment is found to be less than 0.02μB/atom. [ABSTRACT FROM AUTHOR]

Using the surface, interface, and element specificity of x-ray resonant magnetic scattering in combination with x-ray magnetic circular dichroism, we have spatially resolved the polarization, and hence the spin accumulation in Mn high susceptibility material in close proximity to a ferromagnetic layer. The magnetic polarization of Mn and Cu 3d electrons in paramagnetic CuMn layers is detected in a Co/Cu(x)/CuMn structure for varying copper layer thicknesses (x). The size of the Mn and Cu L2–3-edge dichroism shows a decrease in the polarization for increasing copper thickness indicating the dominant interfacial nature of the Cu and Mn spin polarization. The Mn polarization appears to be much higher than that of Cu. [ABSTRACT FROM AUTHOR]

Self-assembled arrays of nanospheres have been used to pattern a Co/Pt multilayer into nanopillars. On top of this has been deposited a Co/Ru multilayer, which is antiferromagnetically coupled. The nanopillars introduce a known structural and magnetic lateral modulation into the multilayer. Soft x-ray magnetic scattering was used to observe the interference patterned from the patterned substrate. This has allowed us to show how the magnetic roughness correlates with the structural roughness and obtain selective magnetometry of the various magnetic elements. [ABSTRACT FROM AUTHOR]

We report results on the effect of the AlOx barrier layer on the magnetic moment of Fe using polarized neutron reflection. The sample has nominal composition 25 nm Au/5 nm Fe/ 1.3 nm AlOx /GaAs(001). The metal deposition was done in ultrahigh vacuum and the Al oxidation was performed in two steps. From the fit to the neutron data we obtain for the magnetic moment of Fe the value (2.164±0.026)μB, very close to the bulk value (2.185μB at room temperature). We conclude that there is no dead layer at the AlOx interface. [ABSTRACT FROM AUTHOR]

U/Fe multilayers have been produced through dc sputtering. The high quality of these multilayers has been confirmed through x-ray reflectivity measurements and fitting to the resultant spectra. These samples are currently the subject of investigations using techniques including polarized neutron reflectivity, conversion electron Mössbauer spectroscopy, and magnetotransport and magneto-optic measurements. In this article, we report on results obtained from a [U 30 Å/Fe 40 Å] × 30 multilayer through resonant magnetic scattering performed on the XMaS beamline at the European Synchrotron Radiation Facility. The asymmetry ratio is defined as (I[SUB+] -I[SUB-])/(I[SUB+]+ I[SUB-]), where I[SUB+](I[SUB-]) is the normalized intensity obtained with circular polarization and the applied field parallel (antiparallel) to the beam direction. Asymmetry data are presented as functions of both energy and momentum transfer. We have identified a Uranium moment with the use of resonant magnetic reflectivity at 12 K. Reversal of the polarity of the asymmetry ratio between the first and second superlattice peaks indicates a nonuniform moment distribution through the uranium layers. Temperature dependence measurements confirm that the moment also exists at room temperature. [ABSTRACT FROM AUTHOR]

Electron scattering mechanisms within metallic multilayers are affected by both structural and magnetic disorders. Off-specular x-ray scattering has long been used to probe the structural interfaces, and it is only recently that it has been applied to the study of magnetic disorder. We compare the resonant magnetic x-ray scattering with off-specular neutron studies from magnetron-sputtered Co/Cu and Co/Ru multilayers grown at the second antiferromagnetic coupling peak. Both techniques yield similar results for the Cu system, and a simple domain model can be applied to extract the magnetic interface morphological parameters. For the Cu system, the in-plane correlation length is field dependent and is 880 ± 20 Å after saturation along the hard axis, but increases to 7000 ± 100 Å after saturation along the orthogonal easy axis. Both systems show strong out-of-plane correlations in both the structural and magnetic disorders. In all cases, the out-of-plane correlation length for the structural interfaces is 200-250 Å, but the ratio of the magnetic to structural correlations length is dependent on the magnitude of the exchange coupling and ranges from 0.4 to 1.4. [ABSTRACT FROM AUTHOR]

Interdiffusion and intermixing have been examined in Fe/Si trilayers prepared with ions of different energies, using the direct ion beam deposition technique. Isotope-pure layers were deposited and spin-polarized neutron reflectivity used to determine the role of Fe diffusion in iron silicide formation. It was found that a nonmagnetic iron silicide was formed that contained Fe from both the top and bottom layers in the trilayer, suggesting complete diffusion across the spacer region. Electron microscopy observations revealed the presence of an iron silicide phase and crystalline interface layers in films prepared with low energy ions (30 eV), while mixed and amorphous-like regions were found at higher ion energies (100 eV). © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Synthesis of a new tetragonal phase at the equiatomic composition in the archetypal binary Fe-Ni phase diagram is reported. This new phase is proposed as a transitional phase linking cubic FeNi with the chemically ordered tetragonal L1 0 FeNi compound, tetrataenite, of interest as a new advanced permanent magnetic material. This new tetragonal phase was created in a selection of nominally equiatomic FeNi alloys, made either from natural Fe and Ni or from natural Fe combined with the 62 Ni isotope, via application of high-strain processing methods followed by an annealing protocol. High-resolution neutron diffraction affirms that all unprocessed samples adopt the A1-type cubic structure (space group Fm 3 ¯ m ) while all fully processed samples adopt the chemically disordered A6-type tetragonal structure (space group I 4/ mmm ). Magnetic characterization documents a decrease in the initial magnetic susceptibility of deformed samples after annealing, evidencing a processing-induced increase in magnetic anisotropy that may be entirely accounted for by the measured tetragonal distortion. It is proposed that this new phase is a precursor to the formation of tetrataenite (L1 0 FeNi, space group P 4 /mmm ), a meteoritic mineral of high magnetization and appreciable magnetocrystalline anisotropy that requires extraordinarily long cooling periods to form in nature. These results furnish new fundamental information as well as engineering insight for terrestrial synthesis of tetrataenite on industrial timescales, with high relevance for the creation of next-generation permanent magnets comprised entirely of easily accessible, earth-abundant elements. [ABSTRACT FROM AUTHOR]

We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices. [ABSTRACT FROM AUTHOR]

Transport measurements are presented on thin-film superconducting spin-valve systems, where the controlled noncollinear arrangement of twoferromagnetic Co layers can be used to influence the superconducting state of Nb. We observe a very clear oscillation of the superconducting transition temperature with the relative orientation of the twoferromagnetic layers. Our measurements allow us to distinguish between the competing influences of domain averaging, stray dipolar fields, and the formation of superconducting spin triplets. Domain averaging is shown to lead to a weak enhancement of transition temperature for the antiparallel configuration of exchange fields, while much larger changes are observed for other configurations, which can be attributed to drainage currents due to spin triplet formation. [ABSTRACT FROM AUTHOR]

Synchrotron X-ray diffraction was used to study the phase transformation processes during the magnetostructural transition in a B2-ordered FeRh (001)-oriented epilayer grown on MgO by sputtering. Out-of-plane lattice constant measurements within the hysteretic regime of the transition reveal a microstructure consistent with the coexistence of lattice-expanded and contracted phases in spatially distinct regions. It was found that the phase separation is more pronounced during cooling than heating. Furthermore, whilst lattice-expanded domains that span the height of the film can be undercooled by several kelvins, there is no equivalent superheating. This asymmetry between the cooling and heating processes in FeRh is consistent with the difference in the kinetics of generic freezing and melting transitions. [ABSTRACT FROM AUTHOR]

Thin films (250-4500 Å) of epitaxial UO2 were produced by reactive sputtering on two different substrate materials: LaAlO3 and CaF2. Using the large enhancement present with resonant x-ray scattering using photons at the uranium M4 absorption edge, antiferromagnetic (AF) order was found in all films. The ordering temperature TN is the same as the bulk, but the films show second-order (continuous) transitions in contrast to the first-order bulk transition. For LaAlO3-based films, an additional strong diffuse magnetic disorder is observed, which is reminiscent of the second-length scale, associated with structural disorder and/or strain. By using a formulation accounting for the strong absorption and coherent nature of the photons, the energy widths at the U M4 resonances can be related to the thickness of the AF region. The LaAlO3-based films do not order magnetically over more than ~600 Å, whereas the CaF2-based film orders throughout. Further, for thicker films (>1000 Å) the fitting procedure shows that the AF order is located at the top of the LaAlO3-based film. This points to the formation in thicker films of a nonmagnetic layer of UO2 adjacent to the substrate, which may have tetragonal symmetry. [ABSTRACT FROM AUTHOR]

In this article we present a detailed investigation of the structural and magnetic properties of exchange biased NiFe (ferromagnet)/FeMn (antiferromagnet) thin films. The influence of the shape anisotropy on exchange bias and the magnetization reversal mechanism in a sample with patterned lines is compared with a continuous two-dimensional reference sample. Polarized neutron reflectivity (PNR) is employed to study the magnetization reversal by analyzing the spin-flip and non-spin-flip reflectivities. PNR measurements show that the magnetization reversal in the reference two-dimensional film and patterned lines is by domain wall motion rather than coherent rotation of magnetization. [ABSTRACT FROM AUTHOR]

Quenched disorder affects how nonequilibrium systems respond to driving. In the context of artificial spin ice, an athermal system comprised of geometrically frustrated classical Ising spins with a twofold degenerate ground state, we give experimental and numerical evidence of how such disorder washes out edge effects and provide an estimate of disorder strength in the experimental system. We prove analyti-cally that a sequence of applied fields with fixed amplitude is unable to drive the system to its ground state from a saturated state. These results should be relevant for other systems where disorder does not change the nature of the ground state. [ABSTRACT FROM AUTHOR]

The thermally driven formation and evolution of vertex domains is studied for square artificial spin ice. A self-consistent mean-field theory is used to show how domains of ground state ordering form spontaneously, and how these evolve in the presence of disorder. The role of fluctuations is studied using Monte Carlo simulations and analytical modelling. Domain wall dynamics are shown to be driven by a biasing of random fluctuations towards processes that shrink closed domains, and fluctuations within domains are shown to generate isolated small excitations, which may stabilize as the effective temperature is lowered. Domain dynamics and fluctuations are determined by interaction strengths, which are controlled by inter-element spacing. The role of interaction strength is studied via experiments and Monte Carlo simulations. Our mean-field model is applicable to ferroelectric 'spin' ice, and we show that features similar to those of magnetic spin ice can be expected, but with different characteristic temperatures and rates. [ABSTRACT FROM AUTHOR]

We have studied how the magnetic properties of oxygen-deficient EuO sputtered thin films vary as a function of thickness. The magnetic moment, measured by polarized neutron reflectometry, and the Curie temperature are found to decrease with reducing thickness. Our results indicate that these surface-induced effects are caused by the reduced number of nearest neighbors, band bending, and the partial depopulation of the 4f states of Eu. [ABSTRACT FROM AUTHOR]

Abstract: We report the measurement of reflected neutron intensity “hysteresis loops” from Co/Ru multilayers that have both antiferromagnetically and ferromagnetically coupled regions. We show that by measuring the four neutron spin-resolved reflectivities at a particular value of wavevector transfer, the normalised value of the relevant magnetic order parameter may be determined. The response of that order parameter to an applied magnetic field may hence be tracked. We have benchmarked our results against conventional magnetometry and magnetotransport measurements. [Copyright &y& Elsevier]

Neutron reflectometry is a well established technique for the study of nanometre scale layered systems which are of direct relevance to a broad range of disciplines cutting across the physical and life sciences [1,2,3]. The second target station (TS2) at ISIS [4] is optimised to produce a large flux of cold neutrons, which when coupled with the large wavelength bandwidth provided by the 10Hz repetition rate offers the possibility for a step change in capability for the study of nanoscale systems. [ABSTRACT FROM AUTHOR]

The reflection of neutrons from a helium surface is observed for the first time. The 4He surface is smoother in the superfluid state at 1.54 K than in the case of the normal liquid at 2.3 K. In the superfluid state we also observe a surface layer ∼200 Å thick which has a subtly different neutron scattering cross section, which may be explained by an enhanced Bose-Einstein condensate fraction close to the helium surface. The application of neutron reflectometry described in this paper creates new and exciting opportunities for the surface and interfacial study of quantum fluids. [ABSTRACT FROM AUTHOR]

Abstract: The effect of the interface on the magnetic moment of Cu/Co,Ni/Cu/Si(001) epitaxial structures was studied by polarised neutron reflection (PNR). The structure consists of a specially designed three-step sample (single 60ÅNi and 10ÅCo films and a 10ÅCo/60ÅNi bilayer) grown under the same conditions in order to eliminate variations in the magnetic properties that could result from different growth environments. Independent structural characterisation of the samples was also determined from grazing incidence X-ray scattering, therefore increasing the confidence of the PNR fits. High precision PNR measurements performed at room temperature up to a wavevector range of yield values of and per Ni atom for the Ni/Cu(001) and Co/Ni/Cu(001) samples, respectively; for the Co layers, the moments per Co atom are and for the Co/Ni/Cu(001) and Co/Cu(001) samples, respectively. Our results show that there are no significant changes in the respective Co and Ni magnetic moments at the Co/Ni interface. [Copyright &y& Elsevier]

Abstract: In the recently developed SESANS technique neutron spin-echo labelling is used to perform small-angle neutron scattering in real space. By using a neutron beam with milliradian divergence it is possible to detect scattering angles of the order of microradians. At the Second Target Station of the neutron spallation source ISIS, UK one of the first group of instruments will be OffSpec, especially designed to obtain information on in-plane inhomogeneities. Here, neutron spin-echo labelling will be employed to obtain real space information of these correlations on a length scale from 10 nm to 30 μm. Other new options that will be possible with the spin-echo components on this instrument are discussed. First test results of broad-wavelength-range time-of-flight reflectometry, making use of HF flippers, are presented. [Copyright &y& Elsevier]

We demonstrate, using spin polarized neutron reflectivity measurements, that one can form a large stack of magnetically decoupled spin-membranes of Gadolinium ions and reduce the effect of the substrate substantially to study short-range two-dimensional (2D) ferromagnetic ordering. No spontaneous magnetization was observed in these membranes as the magnetic field was applied along an in-plane direction. The results are consistent with theoretical predictions of 2D in-plane spin systems having strong interplay of exchange, magneto-crystalline anisotropy and dipolar interactions. These metal–organic multilayer films will enable us to verify various theoretical predictions regarding spin-fluctuations in 2D systems using conventional magnetic measurements and neutron scattering studies. [ABSTRACT FROM AUTHOR]

Abstract: We report on developments in building a compact neutron spin filter based on metastable optical pumping. The apparatus incorporates a high-power Yb-fibre laser, and polarisations of >70% are now routinely achieved in sealed cells prepared at ISIS. A circulating system has also been constructed and initial results with polarised gas are reported. Central to the project is a compact polarisation-preserving compressor and progress on the development of two devices is reported. [Copyright &y& Elsevier]

Magnetic multilayers are known to have behaviour shaped by the intrinsic magnetic properties of their constituents and of their interactions. Multilayers composed of Uranium (5f electrons) and transition metal (3d electrons) provide the unique combination of a potentially large orbital moment with strong electronic hybridisation effects between the extended 5f states and the strongly magnetic 3d states. In this study U/Fe multilayers with layer thicknesses 20 A˚ A˚ and 30 A˚ A˚ were fabricated by dc sputtering in a UHV chamber. X-ray reflectivity (XRR) spectra show good layer structure with little interdiffusion at interfaces. We have investigated the magnetic moment profile normal to the layers by polarised neutron reflectivity (PNR) and specifically whether magnetic moments are induced on the uranium layers by the proximity of the iron layers. The PNR results show a magnetic moment on the iron layers reduced from that of pure bcc iron and they set an upper limit on any moment on the U layers. A more sensitive search for the U moment has involved resonant X-ray magnetic reflectivity measurements at energies around the UMIV edge using different geometries of circular polarisation helicity and applied magnetic field. Some evidence of U moments has been observed. [Copyright &y& Elsevier]

• Field-dependent compensation temperature, which increases with an increase in the applied field. • Multilayer showed field-dependent twisted helical magnetic structure. • Formation of planar 2 π DWs and antiferromagnetic coupling at the interfaces. Rare earth –transition metal heterostructures are known to exhibit a number of magnetic structures at different temperatures and magnetic fields due to the strong antiferromagnetic interaction at the interfaces. Using spin-dependent specular and off-specular polarized neutron reflectivity (PNR), we observed the field-dependent twisted helical magnetic structure with a planar 2 π domain wall (DW) in a Gd/Co multilayer. Macroscopic magnetization measurements revealed the field-dependent compensation temperature, which increases with an increase in the applied field. Specular PNR at 5 K, after field cooling the multilayer in an applied field of 100 Oe, reveals the formation of planar 2 π DWs and antiferromagnetic coupling at the interfaces. Off-specular PNR data from multilayer at 5 K also revealed the development of magnetic inhomogeneities for the central part (thickness ~ 25 Å) of each Gd layer in the multilayer. In contrast, a similar magnetic property of the multilayer was observed at a higher temperature (125 K) on applying a field of 500 Oe. The field-dependent tunability of twisted helical magnetic structures with planar 2 π DWs and the development of highly correlated magnetic inhomogeneities may be key for application in spin-based technology. [ABSTRACT FROM AUTHOR]

Abstract: The prototype of a wavelength-sensitive neutron filter has been realized and tested successfully for the first time. The filter exploits the neutron wavelength dependence of the transparency of 3He gas. The analysis of test results gives high wavelength resolution over the broad wavelength range 0.2–5.2Å. We propose an idea to expand the filter range in the short wavelength direction by use of a cryogenic environment, and also consider the use of media using other than 3He gas. The proposed filter might be used in advanced reflectometers and SANS2D neutron scattering instruments. [Copyright &y& Elsevier]

Abstract: OffSpec is one of the seven new spectrometers operational from day one in the second Target Station (TS2) at the pulsed spallation neutron source ISIS. OffSpec is a time-of-flight, low-background reflectometer specialized in off-specular scattering. It is unique because in addition to conventional reflectivity techniques, it is capable of using the neutron spin-echo angle labelling technique. One of the many possibilities of using this technique is measuring structures on a surface with the length scale of 20nm–15μm. Up to now the calibration of this length scale was made on the prototype instrument in Delft by measuring magnetic line integrals. This showed that the pole shoe design, an essential part of the spin-echo encoding, was not perfect, resulting in a different effective magnetic encoding angle from the physical angle. Recent reflection measurements on gold gratings not only confirmed this but also resulted in a reliable calibration. [Copyright &y& Elsevier]

Factors which contribute to magnetostructural transition control have been demonstrated by study of the effects of Au incorporation on the magnetic and structural character of CsCl-structured equiatomic FeRh thin films. Sputtered films were capped with 2 nm of Au deposited at 873 K and at 323 K and subsequently characterized with magnetometry and synchrotron-based structural probes. Diffusion of Au into the FeRh film layer at 873 K is confirmed by a reduction in the Au capping layer thickness relative to the film capped at 323 K. The impact of Au diffusion on the FeRh magnetostructural character is noted by a decrease in the onset of the transition temperature, a thermally broadened first-order transition and an increased sensitivity of the transition to applied magnetic field. Additionally, magnetization data indicate that Au diffusion causes retention of the ferromagnetic phase well below the normal magnetostructural transition temperature. These results are attributed to a multiphase FeRh film layer created by thermally driven Au diffusion. [ABSTRACT FROM AUTHOR]

The current-induced resonance frequencies of domain walls in parabolic pinning potentials are measured in Gd doped NiFe as a function of doping level. The modification of magnetic properties due to Gd doping results in an order of magnitude increase in resonance frequencies for 10% Gd doping, due to the induced out-of-plane anisotropy, and the resonance frequencies are excited at lower current densities compared to undoped NiFe. These results are reproduced using a one-dimensional model of domain wall resonance, and found to be in good agreement in the small oscillation amplitude limit. [ABSTRACT FROM AUTHOR]

The effect of MgO tunnel barriers on the magnetic moment of ultrathin magnetic Fe and Co layers is studied by polarized neutron reflectivity. The MgO barriers were grown by molecular beam epitaxy using either direct evaporation from a source crystal or evaporation of Mg in an oxygen background atmosphere. A decrease of the magnetic moment is observed for both Fe and Co, and atomic intermixing of 1.5–3.5 ML at interfaces between the Fe, Co, and MgO is determined. Evaporation from a MgO source crystal yields a tunnel layer which displays better stoichiometry and epitaxy than is obtained using the other growth method. [ABSTRACT FROM AUTHOR]

We have studied the reversal of the bulk and interfacial magnetizations of the free layer of a spin valve using soft x-ray resonant magnetic scattering. By dusting the interface of the NiFe free layer with a few angströms of Co, we were able to distinguish between the interfacial and bulk magnetisms by tuning the x-ray photon energy. We measured hysteresis loops of reflected x-ray intensity at selected points in reciprocal space. We find no difference in the switching fields, showing that in transition metal ferromagnets, the exchange interactions are sufficiently strong to prevent a separate interfacial coercivity from arising. [ABSTRACT FROM AUTHOR]

Abstract: We are developing a new neutron reflectometer at the second target station at ISIS. This reflectometer, OffSpec, will be specialised in measuring off-specular reflection and will be equipped with spin-echo components to profit from the new developments in measuring small angles with spin-echo techniques. We recently built a prototype time-of-flight (TOF) spin-echo SANS and/or reflectometer to test and develop new components for OffSpec. Here, we present TOF measurements in spin-echo SANS mode that demonstrates neutron refraction on sets of parallel Cu and Al wires. This demonstrates that we are able to measure angular deviations of the neutron paths of the order of several μrad. Finally, we show results of the first reflection measurements with TOF spin echo. [Copyright &y& Elsevier]

We present magnetometry data for a range of Fe thicknesses grown on GaAs and InAs substrates in order to determine the factors governing the evolution of the magnetic moment of epitaxial Fe grown on a zinc-blende semiconductor. Fe films grown at room temperature by molecular beam epitaxy were characterized structurally and magnetically. The estimated roughness amplitudes were 0.3 ± 0.2 nm for the Fe/GaAs interface and 0.6 ± 0.2 nm for Fe/InAs. We observe a greater reduction of the Fe magnetic moment for films grown on InAs as compared to GaAs, as the Fe films reach a bulk-like moment (within 10% deviation) at a thickness of ∼5.2 nm and ∼2.2 mn, respectively. We conclude that the growth conditions, in particular interface and interdiffusion effects, are the dominant mechanisms influencing the value of the magnetic moment for ultrathin Fe films on GaAs and InAs. [ABSTRACT FROM AUTHOR]