Neutron-depolarization theory in particulate media

Rosman, R.; Rekveldt, M.Th.

doi:10.1103/physrevb.43.8437

Cited by 41 publications

(22 citation statements)

References 10 publications

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“…12,13 Indeed, if f () is a normalized distribution function of the rotation angle of polarization vector in the magnetic field over the beam cross section, then the depolarization elements perpendicular to the applied field D xx ,D xz ,D zx ,D zz and therefore D Ќ will be decreased by the factor…”

Section: A Three-dimensional Depolarization Measurementmentioning

confidence: 99%

Magnetic phase transition in disordered Fe-Ni alloys studied by means of small-angle neutron scattering and three-dimensional analysis of the neutron depolarization

et al. 2001

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The magnetic phase transition in iron-nickel fcc alloys Fe 70 Ni 30 doped by carbon ͑0.7% at.͒ is investigated using the three-dimensional analysis of the neutron depolarization ͑ND͒ and small-angle neutron scattering ͑SANS͒. The coexistence and the growth of two different scale magnetic correlations are observed in a paramagnetic phase as temperature closes to T C . The usual critical fluctuations of a Lorentzian shape with size R c Ͻ200 Å are found by the analysis of SANS intensity I(q). The ND analysis shows also presence of the large scale correlations ͑about 10 3 Ϫ10 4 Å) with the ''squared'' Lorentzian shape. We attribute these large scale correlations to local variations of the Curie temperature T C . The local T C variations are described by the disorder parameters of the system: ͗T C ͘, a spread of T C variations ⌬T C , and characteristic size of the local areas R 0 , where T C variations occur. The ratio between the depth of the T C variations (⌬T C /͗T C ͘) and its characteristic correlation length R 0 /a (a is a lattice constant͒ determines a scenario of the transition: ''percolative'' or ''homogeneous'' ones. At R 0 /aӷ(⌬T C /͗T C ͘) Ϫ2/3 locally ordered ferromagnetic regions appear in paramagnetic phase and form a large percolative cluster. In this case the connectivity length of the ordered regions dominates at the correlation length of thermal fluctuations. Therefore this transition goes in accordance with the ''percolative'' scenario. All three parameters of the transition are obtained from the data of the three dimension analysis of the ND. From the temperature dependence of the magnetization, we found ͗T C ͘ϭ397 Ϯ0.5 K and ⌬T C ϭ4.55Ϯ0.05 K. From ND data we estimated the temperature independent characteristic size R 0 of the T C variations. It is equal to 10 4 Å.

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Section: A Three-dimensional Depolarization Measurementmentioning

confidence: 99%

Magnetic phase transition in disordered Fe-Ni alloys studied by means of small-angle neutron scattering and three-dimensional analysis of the neutron depolarization

et al. 2001

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“…En général, le mesure est faite en transmission ce qui limite sa sensibilité à des études de multicouches (Kraan [21][22]) ou d'empilement de nombreuses couches minces (Por [23]). Pour le principe théorique des mesures de dépolarisation 3D, nous renvoyons aux références suivantes : (Rosman [24][25]) ou (Rekveldt [26]). …”

Section: Mesures De Dépolarisation Sur Des Films Mincesunclassified

Réflectivité hors spéculaire et diffraction de surface

Ott

2001

J. Phys. IV France

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Résumé : La technique de réflectivité de neutrons permet d'obtenir des informations structurelles et magnétiques sur des systèmes multicouches. Dans la géométrie standard de réflectivité spéculaire il est possible d'obtenir des informations sur le profil de densité de longueur de diffusion ou le profil d'aimantation suivant la direction perpendiculaire au plan du système multicouche. Dans ce cours nous allons présenter les différents aspects de la diffusion hors spéculaire en réflectivité de neutrons et montrer de quelle manière elle permet d'accéder à des informations planaires à la fois morphologiques et magnétiques. Nous présenterons les différentes origines de la diffusion hors spéculaire (dans les cas magnétiques et non magnétiques), puis nous décrirons les formalismes permettant de décrire ces phénomènes et enfin nous discuterons quelques exemples de mesures expérimentales sur des systèmes magnétiques.

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“…Here, we will just briefly present the neutron depolarisation in Larmor approach. A detailed overview of the neutron depolarisation theory can be found elsewhere [1,2,7,13].…”

Section: Neutron Depolarisationmentioning

confidence: 99%

“…Rosman and Rekveldt [1] derived the theoretical framework for the determination of the magnetic phase fraction and the (spherical) particle size in the case of monodisperse ferromagnetic particles in a dilute non-magnetic medium from neutron depolarisation experiments. Te Velthuis and co-workers [12] investigated the magnetic particle size obtained by neutron depolarisation and compared it to the ferrite grain size using a numerical model.…”

Section: Introductionmentioning

confidence: 99%

“…Three-dimensional neutron depolarisation (3DND) is a powerful technique to characterise the magnetic microstructure of polycrystalline bulk materials on the (sub)micron scale [1][2][3]. In such measurements, a polarised neutron beam interacts with the local magnetic induction in a magnetised sample, which results in a change of the polarisation vector of the neutron beam upon transmission through the (magnetised) sample.…”

Section: Introductionmentioning

confidence: 99%

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Modelling study on the three-dimensional neutron depolarisation response of the evolving ferrite particle size distribution during the austenite–ferrite phase transformation in steels

Fang

Zwaag

Dijk

2018

Philosophical Magazine

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The magnetic configuration of a ferromagnetic system with mono-disperse and poly-disperse distribution of magnetic particles with inter-particle interactions has been computed. The analysis is general in nature and applies to all systems containing magnetically interacting particles in a non-magnetic matrix, but has been applied to steel microstructures, consisting of a paramagnetic austenite phase and a ferromagnetic ferrite phase, as formed during the austenite-to-ferrite phase transformation in low-alloyed steels. The characteristics of the computational microstructures are linked to the correlation function and determinant of depolarisation matrix, which can be experimentally obtained in three-dimensional neutron depolarisation (3DND). By tuning the parameters in the model used to generate the microstructure, we studied the effect of the (magnetic) particle size distribution on the 3DND parameters. It is found that the magnetic particle size derived from 3DND data matches the microstructural grain size over a wide range of volume fractions and grain size distributions. A relationship between the correlation function and the relative width of the particle size distribution was proposed to accurately account for the width of the size distribution. This evaluation shows that 3DND experiments can provide unique in situ information on the austenite-to-ferrite phase transformation in steels.

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Neutron-depolarization theory in particulate media

Cited by 41 publications

References 10 publications

Magnetic phase transition in disordered Fe-Ni alloys studied by means of small-angle neutron scattering and three-dimensional analysis of the neutron depolarization

Magnetic phase transition in disordered Fe-Ni alloys studied by means of small-angle neutron scattering and three-dimensional analysis of the neutron depolarization

Réflectivité hors spéculaire et diffraction de surface

Modelling study on the three-dimensional neutron depolarisation response of the evolving ferrite particle size distribution during the austenite–ferrite phase transformation in steels

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