Neutrons are spin 1/2 particles that interact with magnetic induction fields via the Zeeman interaction. This interaction is both rather large and simple to describe. Several neutron scattering techniques have been developed to use thermal neutrons to characterize magnetic micro and nanostructures.
Polarized small-angle neutron scattering (SANS) Small-angle neutron scattering is a technique which is especially suited for the study of nanoparticles. It has for example been used extensively for the study of ferrofluids. More recently, polarized SANS has become more widely available and a wide range of study have been performed. Polarized SANS allows either to probe the internal structure of magnetic nanoparticles via the measurement of the magnetic form factor or the magnetic interactions between magnetic nanoparticles via the structure factor. In a few cases, Polarized Grazing Incidence SANS was performed on magnetic systems A few polarized neutrons SANS spectrometers are available across the world:
D33 at the Institut Laue-Langevin (ILL) in Grenoble France PA20 at CEA Laboratoire Léon Brillouin (LLB) in Saclay, France (CEA Saclay site) SANS-I and KWS-1 and KWS-2 at the Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II) in Garching, Germany V4 at Helmholtz Zentrum Berlin
Polarized neutron reflectometry Polarized neutron reflectometry allows probing magnetic thin films and ultra-thin films. The polarized reflectivity measurements allow measuring the magnitude and directions of the magnetic induction in magnetic heterostructures with a depth resolution on the order of 2-3 nm for films with thicknesses ranging from 5 to 100 nm. A number of polarized neutrons reflectometers are available across the world:
Platypus at ANSTO in Sydney, Australia C5 spectrometer at NRC Canada Chalk River Labs in Chalk River, Canada. D3 reflectometer at NRC Canada Chalk River Labs in Chalk River, Canada. D17, SuperADAM at the Institut Laue-Langevin (ILL) in Grenoble, France PRISM (alternate) at CEA Laboratoire Léon Brillouin (LLB) in Saclay, France N-REX+, MIRA[link removed], TREFF@NoSpec and MARIA at the Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM II) in Garching, Germany REFLEX Archived 2008-04-04 at the Wayback Machine and REMUR at Joint Institute for Nuclear Research IBR-2 in Dubna, Russia AMOR Archived 2007-07-14 at the Wayback Machine at the Paul Scherrer Institute (PSI) in Villigen, Switzerland SURF, CRISP, INTER, Offspec and polREF at the ISIS neutron source (ISIS) in Oxfordshire, United Kingdom NG1, NG7 at the NIST Center for Neutron Research (NCNR) in Gaithersburg, Maryland, United States Magnetism at the Spallation Neutron Source (ORNL) in Oak Ridge, Tennessee, United States A catalogue of neutron reflectometers is available at www.reflectometry.net.
Polarized Neutron Radiography and Tomography
Precession techniques The neutron precession in an induction field is expressed as d M → d t = γ n M → × B → ( r ) {\displaystyle {\frac {d{\overrightarrow {M}}}{dt}}=\gamma _{n}{\overrightarrow {M}}\times {\overrightarrow {B}}(r)} where M → {\displaystyle {\overrightarrow {M}}} is the neutron magnetic moment, B → {\displaystyle {\overrightarrow {B}}} is the local magnetic induction at the neutron position r ( t ) {\displaystyle r(t)} and γ n = g n μ N / ℏ {\displaystyle \gamma _{n}=g_{n}\mu _{N}/\hbar } is the neutron gyromagnetic ratio. For neutrons, the gyromagnetic ratio is γ n = g n μ N ℏ = 183 × 10 6 r a d . s − 1 . T − 1 = 29.2 M H z . T − 1 {\displaystyle \gamma _{n}=g_{n}\mu _{N}\hbar =183\times 10^{6}rad.s^{-1}.T^{-1}=29.2MHz.T^{-1}} (note that for neutrons g factor is negative and equal to -3.83).
Bulk systems Neutron radiography can be used to map the distribution of an induction field B → ( r → ) {\displaystyle {\vec {B}}({\vec {r}})} in space. In order to perform such experiments, the neutron beam is initially polarized, it interacts with the induction field of interest and the neutron precession is measured with a neutron analyzer in front of the 2D detector. The beam can be either polarized with supermirrors or with polarized 3He gaz
… excerpt ends here. Continue reading the full article.
