LENS Webinar #2, New Directions in Instrumentation: Reflectometry

Artist’s impression of self-assembled magnetic nanoparticles and scattering of a mesocrystal. CREDIT: Artur Glavic

Artur Glavic: Neutrons for Magnetic Nanostructures on Surfaces: Beyond the Specular Intensity Wars

25 June 2020, 11:00am CEST

Chair: Christof Niedermayer, Paul Scherrer Institute

Join via Zoom: https://ill.zoom.us/j/99877481390

Introduction to LENS webinar series: New Directions in Instrumentation
Christof Niedermayer, PSI

“Neutrons for Magnetic Nanostructures on Surfaces: Beyond the Specular Intensity Wars”
Artur Glavic, PSI

Q & A

End of programme

ABSTRACT: Polarized Neutron Reflectometry (PNR) is a great method to study magnetism of surface near structures on the nm scale. It is especially useful for functional materials and fundamentals of nano magnetism. The applications of the technique and the related grazing incidence scattering include multiferroic heterostructures, correlated electron systems, exchange bias, superconductors, magnetic nanoparticles and spin textures like skyrmions. Many of these systems have in common that the sample sizes are small, leading to intensity limited experiments.

RAINBOWS concept of polychromatic reflectometry: D50@ILL [1]

The special requirements of the reflectometry method on scattering geometry, resolution and the specular condition allowed several developments for instrumentation to potentially gain orders of magnitude in signal and thus reduce measurement time and required sample size. Many of the proposed special techniques – white beam analysis as implemented in RAINBOWS, focusing reflectometry optimally employed with the Selene neutron guide or a combination of the two currently commissioned at the CANDOR instrument – can reach a factor of 10 to 100 gain compared to conventional collimated beam techniques on top of any gain from new sources or increased perpendicular focusing. With these developments the limits of PNR are expected to be at measurement times of seconds for standard samples and size limits pushed below 1 mm².

Concept of the CANDOR focusing and polychromatic reflectometer. CANDOR@NIST [2]

I will briefly present the PNR technique and its application to magnetic systems. Then I will explain the experimental peculiarities that allow for these special developments. Building on this one can follow the previous mentioned novel instrument schemes and how they can achieve such great gains that are not possible with other neutron techniques. For the Estia instrument at ESS I will go in more detail on how other instrument components like spin polarizers and analyzers can be adopted to the new techniques.

While it is exciting to work with these novel instruments, it now seems that we have reached the point where, for the magnetic science case, no further intensity gains will lead to more scientific results. I will therefore concentrate in the second part of the talk on the off-specular and GISANS techniques, that give inside into the in-plane magnetic order. In these measurements the tricks used for the specular reflectivity fail and, on the other hand, these are the techniques mostly suffering from signal limitations right now. How could instruments of the future help us explore more in these active fields of magnetic nanostrucutres?

Focusing Selene neutron guide for the Estia instrument at ESS. Estia@ESS [3]

[1] R. Cubitt, J. S. Ruiza and W. Jark, Journal of Applied Crystallography, 51, 257-263, (2018)

[2] CANDOR instrument at NIST, more information online at https://www.nist.gov/ncnr/chrns-candor-white-beam-reflectometer

[3] K.H. Andersen, et all., Nuc. Inst. Meth. A, 957, 11-13, (2020)

Artur Glavic is an instrument scientist at Switzerland’s Paul Scherrer Institute (PSI) where he is developing the polarized neutron reflectometer Estia for the European Spallation Source (ESS). He is also part-time local contact for the AMOR instrument at PSI’s SINQ. His personal research interest is in complex magnetism in oxide thin films. Before PSI, Artur worked at the USA’s Oak Ridge National Laboratory (2012-2015) and Forschungszentrum Jülich (2007-2012). As of May 2020 he leads PSI’s contributions to ESS as the ESS Project Manager.

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