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Ni-aluminides are an important class of intermetallics from technological point of view. Ni-Al phase diagram has been studied in detail experimentally as well as theoretically. It is known that if annealed at low temperature, the first alloy phase is usually NiAl3 according to Bené's rule. It is also understood that heat of formation may get modified by local densities of the constituents forming the alloy. In this regard, it is important to identify a kinetic length scale for defining "local density" in a system. We have deposited ultrathin multilayers of Ni and Al of layer thickness in tens of nanometres with Ni:Al stoichiometric ratio as 3:1 and 1:3, respectively. Considering these stoichiometry, Ni3Al and NiAl3 are the thermodynamically favoured alloy phases in these samples. We used x-ray reflectivity, polarized neutron reflectivity, x-ray diffraction, and secondary ion mass spectroscopy to follow the alloy formation after annealing and identified the alloy phases at interfaces with nanometre resolution. Diffusion length of Ni and Al was obtained using Darken's law. Our results predict that 'diffusion length' is the unique length scale that connects kinetics to local density. In another interesting observation, using "virtual Kirkendall markers" at the interfaces, we showed asymmetry in consumption of Al for alloy formation, at Al on Ni (Al/Ni) and Ni on Al (Ni/Al) interfaces by comparing as-deposited and annealed states with respect to the markers. [ABSTRACT FROM AUTHOR]

The experimental evidence of the exchange bias (EB) effect in epitaxial heterostructures of ferromagnetic La0.67Sr0.33MnO3 (LSMO) and paramagnetic LaNiO3 (LNO) grown on MgO(001) substrates is reported. The macroscopic magnetization measurements show a clear indication of EB in LNO/LSMO and LSMO/LNO/LSMO heterostructures. The strength of the exchange coupling rapidly reduces as the temperature is increased and almost vanishes above 50 K. Using spin dependent polarized neutron reflectometry (PNR) detailed depth dependent magnetization profiles of the heterostructures are investigated to understand the role of interface magnetism in the observed EB. PNR results establish the emergence of the interfacial ferromagnetic LNO layer of thickness ≈22–35 Å (≈6–9 unit cell) and magnetization ≈80 emu cc−1 at the LNO/LSMO interface for T < 100 K. The PNR results also show both ferromagnetic and anti‐ferromagnetic coupling between the LSMO and interfacial LNO layers, which may be dependent on the stacking order. The emergence of ferromagnetism in the interfacial paramagnetic LNO layer with unexpected EB in these heterostructures suggests a promising platform toward the effective realization of magnetic devices. [ABSTRACT FROM AUTHOR]

A difference in nuclear and magnetic roughness in Fe/Ge thin film was observed by specular polarized neutron reflectometry. The study also shows asymmetric magnetic scattering length density distributions at Fe on Ge and Ge on Fe interfaces. Using specular and diffuse x-ray reflectivity measurements we could estimate the depth of interdiffusion of Fe and Ge at two interfaces. We also observed that the interface magnetic moments are also strongly dependent on the crystalline state of Fe and Ge as well as the deposition sequence. The difference between nuclear and magnetic roughness at magnetic-semiconductor interfaces will play important role in spintronics. [ABSTRACT FROM AUTHOR]

Fe/Ge multilayer sample was grown on Si(100) substrate by rf sputtering. X-ray diffraction shows that the Fe layers are polycrystalline whereas the Ge layers are amorphous in this sample. X-ray reflectometry and unpolarized neutron reflectometry techniques have been used to determine the structural parameters viz. individual layer thickness, interface roughness, and the density of the layers. Polarized neutron reflectometry has given magnetic moment depth profile for the multilayer thin film. There is a large reduction in magnetic moment for Fe atom on an average in the Fe layers. Magnetic moments of Fe at the interfaces are lower compared to the regions away from the interfaces. There is an asymmetry between magnetic moments at Fe on Ge interfaces and Ge on Fe interfaces as well. Superconducting quantum interference device measurement indicates that the sample is ferromagnetic at room temperature with a lower magnetic moment compared to bulk iron. [ABSTRACT FROM AUTHOR]

Nickel-Germanides are an important class of metal semiconductor alloys because of their suitability in microelectronics applications. Here we report successful formation and detailed characterization of NiGe metallic alloy phase at the interfaces of a Ni-Ge multilayer on controlled annealing at relatively low temperature ~ 250 °C. Using x-ray and polarized neutron reflectometry, we could estimate the width of the interfacial alloys formed with nanometer resolution and found the alloy stoichiometry to be equiatomic NiGe, a desirable low-resistance interconnect. We found significant drop in resistance (~ 50%) on annealing the Ni-Ge multilayer suggesting metallic nature of alloy phase at the interfaces. Further we estimated the resistivity of the alloy phase to be ~ 59µΩ cm. [ABSTRACT FROM AUTHOR]

The present study concentrates on the measurement of gain in the flux of cold neutrons emanating from an H2O ice moderator when it is cooled from ambient to a cryogenic temperature. The temperature of neutrons when the moderator is at cryogenic temperature has been determined from this gain. The integrated cold neutron flux is obtained by using a polycrystalline beryllium low pass filter in the path of a scattered neutron beam. A gain of about 7 in the cold neutron flux and a neutron temperature of about 100 K have been obtained when the temperature of water ice was reduced to 77 K. [ABSTRACT FROM AUTHOR]

At photon energies close to absorption edges in the soft x-ray range, the complex index of refraction, n=1-δ-iβ, of organic materials varies rapidly as a function of photon energy in a manner that strongly depends on the chemical moieties and functionalities present in the material. The authors present details of how these molecular structure specific variations in the complex index of refraction can be utilized to enhance and tune the contrast in reflectivity experiments of organic films. This near edge contrast enhancement mimics the specific contrast achieved through deuterium labeling in neutron reflectivity (NR). This relatively new x-ray approach, resonant soft x-ray reflectivity (RSoXR), thus combines aspects of NR and conventional x-ray reflectivity (XR), yet does not require special chemical procedures. The capabilities of RSoXR are exemplified using a number of polymeric bi- and multilayers. Furthermore, a direct comparison of RSoXR to conventional x-ray reflectivity and NR for polystyrene and poly(methyl methacrylate) bilayers verifies that RSoXR is an excellent alternative tool for the characterization of organic thin films. The influence of the longitudinal and transverse coherence properties as well as the divergence of the x-ray or neutron beam on the capabilities and limitations of each reflectivity variant is discussed. [ABSTRACT FROM AUTHOR]

The article presents several studies on the polarized neutron reflectometer instrument. It determines X-ray reflectivity (XRR) and polarized neutron reflectivity (PNR) as complementary techniques used to obtain exact stoichiometry of phases at the interfaces in thin films. It suggests that polarized diffuse neutron reflectivity enables researchers to characterize morphology of magnetic interface.