Science

POLREF's fundamental capability is the Neutron Reflectivity (NR) technique, which is sensitive to buried interfaces (the boundary between two materials) and surfaces. The polarised aspect of the beamline (PNR) makes the reflectivity sensitive to magnetism, the study of which is the primary purpose of POLREF. These two techniques combined make the beamline very flexible, hence its science remit is wide covering biology, chemistry, soft matter and physics.  

Why are people interested in interfaces and surfaces? Interfaces are scientifically crucial as they allow symmetry breaking, leading to many novel and interesting phenomena, such as ferroelectricity and superconductivity. Modern technology is dependent on interface physics (e.g. 2007 Nobel Prize winning work on the Giant Magnetoresistance Effect used in data storage). Most thin film media used in planar technologies rely on stacked layers of material, comprising many buried interfaces. This is not just the case for metals magnetic systems, for example biological interfaces are crucial for life and consist of stacked layers of proteins and the surfaces of catalysts are also critical to how they function.  Reflectivity is unique in its ability to probe these buried interfaces and surfaces.

Reflectivity occurs whenever there is an equivalent refractive index change across a material boundary/interface. As a result it is very sensitive to the structural/magnetic profile of interfaces. NR/PNR allows both the structural and magnetic Scattering Length Density (SLD) depth profiles to be obtained.  The SLD can then be deconvolved into three fundamental properties: (1) The nuclear and magnetic layer thicknesses, (2) interface roughness/grading (3) density/composition. These three properties can be linked back to a wealth of technological and scientifically relevant phenomena. Another major advantage of PNR is that it is a depth-resolved vector magnetometer in contrast to most magnetometry techniques, which measure the bulk average.

Example applications

• Spintronics
  
• Magnetic nanostructures
• Complex biological layered structures
• Corrosion studies
• Fundamental magnetism and superconductivity
• Electrochemistry

Techniques

• Horizontal and vertical sample geometry Neutron Reflectometry (NR).
• Horizontal sample geometry Polarised Neutron Reflectometry (PNR).
• Horizontal sample geometry Polarisation Analysis (PA).
• Off-specular NR/PNR/PA.
• Magnetic layer contrast variation. Now with quick switching between NR/PNR  at the touch of a button for rapid prototyping.
• Isotopic contrast variation.
  

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