ISSN 1027-4510, Journal of Surface Investigation. X-ray, Synchrotron and Neutron Techniques, 2012, Vol. 6, No. 5, pp. 784–795. © Pleiades Publishing, Ltd., 2012. Original Russian Text © S.V. Kozhevnikov, F. Radu, Yu.V. Nikitenko, V.L. Aksenov, 2012, published in Poverkhnost’. Rentgenovskie, Sinkhrotronnye i Neitronnye Issledovaniya, 2012, No. 10, pp. 3–17. 784 INTRODUCTION This study was carried out to obtain neutron mag- netic resonance (NMR) in a magnetic film. The NMR phenomenon that occurs during neutron propagation through a spatial region in which there are static and rotating magnetic fields was first considered in the papers of Rabi [1, 2]. This phenomenon lies in the fact that a periodic-in-time change in the probability of the neutron spin (magnetic moment) flip is observed when the frequency of the rotating magnetic field (RMF) coincides with the Larmor frequency of the neutron spin precession around the induction vector of the static magnetic field (SMF). For the probability of the spin flip of a particle propagating in a static magnetic field H and a magnetic field H 1 , which is perpendicular to H and rotating with the circular frequency ω, over the time t, the following expression was obtained [1, 2]: (1) where ω 0 = γH, ω 1 = γH 1 , and γ is the gyromagnetic ratio of the particle. NMR was first used to measure the neutron magnetic moment [3]. Afterwards, the record-breaking one-hundred-thousandth measure- ment accuracy for the neutron magnetic moment was reached using NMR in 1952. Then NMR was used to obtain beams of neutrons with specific energy and polarization characteristics. So a NMR-based spin flipper [4] and neutron monochromator [5] were pro- posed and used afterwards. It was proposed that NMR be used to decelerate [6] and accelerate [7] neutrons ( ) ( )) ( ) ( ) 2 2 2 1 1 0 12 2 2 2 1 0 sin 2, P t   =ω ω + ω -ω     × ω + ω -ω     and to construct a coherent divisor of the neutron- wave front [8]. Unlike the widely used nuclear magnetic reso- nance, up to now, neutron magnetic resonance has not been used to study the properties of condensed media and, in particular, nanostructures. What arguments can we present to justify the use of NMR in the study of layered structures? The first of them includes deter- mination of the absolute magnetic induction in a mat- ter using the resonance frequency. The second involves determination of the frequency dependence of the spatial susceptibility profile of the oscillating magnetic field. The third one involves determination of the medium’s parameters characterizing the degree of induction-vector magnetic nonuniformity using the NMR width. The difficulties in the recording of neu- tron resonance in a thin magnetic layer are related to the small time of neutron exposure to the oscillating magnetic field, which, accordingly, leads to a low neu- tron spin-flip probability. Indeed, it follows from (1) that, for example, the neutron spin-flip probability is an extremely small quantity W ≈ 10 –12 during the propagation of a neutron with a velocity of 10 m/s through a magnetic layer with a thickness of 1 nm, in which the magnetic induction of the rotating field is B 1 = 10 –3 kG. The authors of [9–11] solved the prob- lem of neutron propagation in a layered multistructure located in a rotating magnetic field. They showed that the spin-flip probability can nevertheless be suffi- ciently high because of the use of a neutron wave reso- nator [12, 13] increasing the time required for the neu- tron to be in the magnetic field. The energy exchange between the neutron and the rotating magnetic field occurs during neutron resonance along with a change in the neutron spin state. As a result, in the case of Reflection of Neutrons from a Magnetic Film Placed in Static and Oscillating Magnetic Fields S. V. Kozhevnikov a , F. Radu b , Yu. V. Nikitenko a , and V. L. Aksenov a, c a Laboratory of Neutron Physics, Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia e-mail: kzh_sv@mail.ru, nikiten@nf.jinr.ru, aksenov@nf.jinr.ru b Helmholtz-Zentrum Berlin für Materialen und Energie, Albert-Einstein-Strasse 15, 12489 Berlin, Germany e-mail: Radu@helmholtz-berlin.de Received April 24, 2012 Abstract—Measurements of polarized-neutron reflection from magnetic films placed in a static magnetic field and in an oscillating magnetic field perpendicular to it are described. The process of diffuse neutron scat- tering involving energy transfer from a RF electromagnetic field to neutrons has been studied. Neutron mag- netic resonance has been detected, and splitting of the polarized beam of neutrons reflected from a film has been discovered. DOI: 10.1134/S1027451012100096