Theoretical description of neutron resonances in multilayer systems

Radu, F.; Ignatovich, V. K.

doi:10.1016/s0921-4526(00)00285-4

Cited by 28 publications

(22 citation statements)

References 7 publications

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“…However, there are drawbacks as well, namely that the cell absorption is not negligible and the flipping ratio seemed to be lower as compared to the case of the supermirror. In the present experiment these difficulties, especially the reduced neutron transmission, were successfully compensated by using an enhancement technique provided by the sample design as a neutron resonator [9,10].Recently (Nov-2002), the neutron polarization of the 3 He spin-filter reached an outstanding value of 94% [8] with a neutron transmission of about 40%. Therefore the spin-flip ratio became comparable to the one provided by the supermirror.…”

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“…In both cases the neutron density in the system is enhanced [9,10] for definite incident neutron energies and one uses this phenomenon to increase the sensitivity to magnetic and nonmagnetic inhomogeneities and to non-collinear magnetic spin arrangements at the interface. As long as the observed effect takes place in the total reflection region, the scattered intensity is essentially the same as the incident intensity.…”

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confidence: 99%

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Spin-resolved off-specular neutron scattering from magnetic domain walls using the polarized gas spin filter

Radu

Vorobiev²,

Major³

et al. 2003

Physica B: Condensed Matter

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We report on the use of the polarized 3 He gas filter and neutron resonant enhancement techniques for the measurement of spin-polarized diffuse neutron scattering due to ferromagnetic domains. A CoO/Co exchange biased bilayer was grown on a Ti/Cu/Al2O3 neutron resonator template. The system is cooled in an applied magnetic field of Ha = 2000 Oe through the Néel temperature of the antiferromagnet to 10 K where the applied magnetic field is swept as to measure the magnetic hysteresis loop. After the second magnetization reversal at the coercive field Hc2 = +230 Oe, the system is supposed to approach the original magnetic configuration. In order to prove that this is not the case for our exchange biased bilayer, we have measured four off-specular maps I++, I+−, I−+, I−− at Ha ≈ +370 Oe, where the Co magnetic spins were mostly reversed. They show a striking behavior in the total reflection region: while the nonspin-flip scattering exhibits no diffuse reflectivity, the spin-flip scattering shows strong diffuse scattering at incident angles which satisfy the resonance conditions. Moreover the spin-flip off-specular part of the reflectivity is asymmetric. The I−+ intensity occurs at higher exit angles than the specularly reflected neutrons, and the I+− intensity is shifted to lower angles. Their intensities are noticeably different and there is a splitting of the resonance positions for the up and down neutron spins (αAdditionally, a strong influence of the stray fields from magnetic domains to the resonance splitting is observed.PACS numbers: 75.60.Jk, 75.70.Cn, 61.12.Ha Keywords: spin-resolved neutron reflectivity, off-specular scattering, 3 He neutron spin filter, neutron resonator, exchange biasThe exchange bias (EB) phenomenon is associated with an exchange coupling between a ferromagnetic (F) and an antiferromagnetic (AF) layer across their common interface, resulting in an unidirectional magnetic anisotropy and a shift of the magnetic hysteresis by an exchange bias field H EB [1]. A remarkable effect related to the exchange bias is the asymmetry of the magnetization reversal, which is best revealed by neutron scattering [2,3,4,5]. The first magnetization reversal after field cooling is dominated by domain wall movement, whereas all subsequent reversals proceed essentially by rotation of the magnetization. In the present work we report on neutron off-specular diffuse scattering experiments performed at applied magnetic fields close to the second coercive field H c2 supplementing the previous results at fields near the first coercive fieldThe polarized 3 He gas spin filter was recently used for the first time [6] in a reflectivity experiment to measure diffuse scattering from thin magnetic films. The device itself is a cylindrical cell of 100 mm in length and 50 mm in diameter, filled with 0.5 bar 3 He gas. After filling, * Permanent address: Department of Experimental Physics, National Institute of Physics and Nuclear Engineering, P. O. BOX MG-6, 76900, Magurele, Romania. † Corresponding author. Tel: +49-234-322-...

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Spin-resolved off-specular neutron scattering from magnetic domain walls using the polarized gas spin filter

Radu

Vorobiev²,

Major³

et al. 2003

Physica B: Condensed Matter

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“…1a). Below the critical edge at the resonance conditions the neutron wave function density is resonantly enhanced in the channelling layer B [10] and hence all the neutron interactions such as the spin-flip cross section [11], the diffuse scattering [12,13], alpha-particles [14] or gammaquanta [15] emission.Let r BA(BC) be the complex reflection amplitudes of the tunnelling layer and of the reflector layer, from inside out. Let k B = k 2 0 − u ± µB be the normal component of neutron wave-vector in the investigated layer of thickness d. The complex reflection coefficients can be calculated numerically based on the parameters of the reflector layer, the tunnelling layer, and of the resonant layer.…”

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Polarized neutron channeling as a tool for the investigations of weakly magnetic thin films

et al. 2016

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We present and apply a new method to measure directly weak magnetization in thin films. The polarization of a neutron beam channeling through a thin film structure is measured after exiting the structure edge as a microbeam. We have applied the method to a tri-layer thin film structure acting as a planar waveguide for polarized neutrons. The middle guiding layer is a rare earth based ferrimagnetic material TbCo5 with a low magnetization of about 20 mT. We demonstrate that the channeling method is more sensitive than the specular neutron reflection method.PACS numbers: 3.75. Be, Magnetic nanomaterials are widely used in practical applications and in fundamental physics. Therefore the development of new methods providing enhanced sensitivity for the characterization of their magnetic properties is a challenge. One of the well-established methods for magnetic thin films and nanostructures characterization is the Polarised Neutron Reflectometry (PNR) technique [1]. Its strength is the unique ability to probe the magnitude and the direction of the magnetization vector as a function of the depth in magnetic heterostructures. For collinear spin configurations, the PNR method resolves the depth dependence of the scattering length densities (SLD) ρ(z) which depends on the neutron polarization: ρ ± (z) = ρ 0 (z) ± cB(z). Here ρ 0 (z) and B(z) are the depth profiles of the nuclear SLD and the magnetic induction. By measuring reflectivities of spin-up and spin-down neutrons and fitting them to theoretical values one can extract the SLD depth profile and the depth dependence of the induction in a film. The method is routinely used for the characterization of ferromagnetic systems with rather high magnetization (about 0.3 -2 T). Being a model dependent method it leads to the nonuniqueness of the resulting set of parameters describing the system. As a result, the accuracy of the fitted parameters depends both on the adequacy of a model and on the quality of the experimental data. For systems with weak magnetization (∼ 10 mT), PNR requires very long measurement times (∼ 10 2 hours) in order to achieve sufficient statistics. This is usually not compatible with standard neutron reflectometry experiments.Weak magnetizations, typically less than 100 mT, are characteristic of ferrimagnetic materials or magnetic oxides. Magnetic materials such as Fe 3 O4, CoFe 2 O 4 , BiFeO 3 , GaFeO 3 , Bi 3 Fe 5 O 12 , NiCoMnAl are being increasingly studied because of their specific properties, either their electronic properties [2], their magneto-electric properties [3], their magneto-optical [4] or their magneto caloric properties [5]. The study of these materials is often limited by the weakness of the magnetic interfacial effects that are of interest. While XMCD [6] is a very sensitive technique to probe surface magnetism, it is sometimes rather difficult to apply to complex heterostructures as used in spintronic devices. Also, the XRMS [7] technique cannot access thicker layer structure because the soft x-ray penetration depth is on the order...

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“…The neutron standing waves method was developed in [10]. It is based on the theory of neutron resonances in layered structures described in [11]. The neutron standing waves can be registered as minima at the total reflection plateau or maxima of a characteristic radiation: gamma-quanta [12], alpha-particles [13], off-specular neutron scattering [14,15], neutron channelling [16] or spin-flip of polarized neutrons [17].…”

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Neutron resonances in planar waveguides

Кожевников

Ignatovich

Петренко

et al. 2016

J. Exp. Theor. Phys.

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Results of experimental investigations of a neutron resonances width in planar waveguides using the time-of-flight reflectometer REMUR of the IBR-2 pulsed reactor are reported and comparison with theoretical calculations is presented. The intensity of the neutron microbeam emitted from the waveguide edge was registered as a function of the neutron wavelength and the incident beam angular divergence. The possible applications of this method for the investigations of layered nanostructures are discussed.

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Theoretical description of neutron resonances in multilayer systems

Cited by 28 publications

References 7 publications

Spin-resolved off-specular neutron scattering from magnetic domain walls using the polarized gas spin filter

Spin-resolved off-specular neutron scattering from magnetic domain walls using the polarized gas spin filter

Polarized neutron channeling as a tool for the investigations of weakly magnetic thin films

Neutron resonances in planar waveguides

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