Effect of Dzyaloshinski-Moriya interaction on elastic small-angle neutron scattering

Michels, Andreas; Mettus, Denis; Honecker, Dirk; Metlov, Konstantin L.

doi:10.1103/physrevb.94.054424

Cited by 26 publications

(68 citation statements)

References 52 publications

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“…Supported by theory [27], we provide here experimental evidence for the generic impact of the DMI on the spin microstructure of polycrystalline defect-rich ferromagnets. Examples for such systems are nanomagnets, which are characterized by a large volume fraction of internal interfaces (e.g., grain boundaries), and mechanically-deformed metals containing a large density of dislocations.…”

supporting

confidence: 61%

“…we have theoretically investigated in Ref. 27 the impact of the DMI on the magnetization distribution M(r) and on the ensuing magnetic SANS cross section. In addition to the DMI energy, we have taken into account the energies due to the isotropic exchange interaction, magnetic anisotropy, and the magnetostatic interaction.…”

mentioning

confidence: 99%

“…The mechanisms by which nanoscale spin disorder in magnetic materials is generated are essentially related to (i) spatial variations in the magnetic anisotropy field H p (r), and to (ii) spatial variations in the magnetic materials parameters, most notably the local saturation magnetization M s (r). Both sources of magnetization inhomogeneities-modeling the effect of the defects-are taken into account in the magnetic SANS theory [27]. To be more specific, forces due to the distortion of the crystal lattice in the vicinity of a microstructural defect tend to rotate the local magnetization vector field M(r) along the main axes of the system of internal stresses (so-called magnetoelastic coupling), while magnetocrystalline anisotropy tries to pull the magnetic moments along the principal axes of the crystal [29].…”

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confidence: 99%

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Microstructural-defect-induced Dzyaloshinskii-Moriya interaction

et al. 2019

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The antisymmetric Dzyaloshinskii-Moriya interaction (DMI) plays a decisive role for the stabilization and control of chirality of skyrmion textures in various magnetic systems exhibiting a noncentrosymmetric crystal structure. A less studied aspect of the DMI is that this interaction is believed to be operative in the vicinity of lattice imperfections in crystalline magnetic materials, due to the local structural inversion symmetry breaking. If this scenario leads to an effect of sizable magnitude, it implies that the DMI introduces chirality into a very large class of magnetic materialsdefect-rich systems such as polycrystalline magnets. Here, we show experimentally that the microstructural-defect-induced DMI gives rise to a polarization-dependent asymmetric term in the small-angle neutron scattering (SANS) cross section of polycrystalline ferromagnets with a centrosymmetric crystal structure. The results are supported by theoretical predictions using the continuum theory of micromagnetics.This effect, conjectured already by Arrott in 1963, is demonstrated for nanocrystalline terbium and holmium (with a large grain-boundary density), and for mechanicallydeformed microcrystalline cobalt (with a large dislocation density). Analysis of the scattering asymmetry allows one to determine the defect-induced DMI constant, D = 0.45 ± 0.07 mJ/m 2 for Tb at 100 K. Our study proves the generic relevance of the DMI for the magnetic microstructure of defect-rich ferromagnets with vanishing intrinsic DMI. Polarized SANS is decisive for disclosing the signature of the defectinduced DMI, which is related to the unique dependence of the polarized SANS cross section on the chiral interactions. The findings open up the way to study defectinduced skyrmionic magnetization textures in disordered materials.

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confidence: 61%

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confidence: 99%

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confidence: 99%

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Microstructural-defect-induced Dzyaloshinskii-Moriya interaction

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“…Whilst for bulk ferromagnets the theory of magnetic SANS has recently been developed 30–35 , for isolated magnetic nanoparticles in a nonmagnetic matrix the theoretical description of magnetic SANS is still in its infancy; in particular, when microstructural-defect or particle-shape-induced spin misalignment is present. In fact, the magnetic SANS theory of nanoparticles remains an open problem that needs to be resolved for an accurate analysis of experimental data.…”

Section: Introductionmentioning

confidence: 99%

Small-angle neutron scattering modeling of spin disorder in nanoparticles

Vivas

Yanes

Michels

2017

Sci Rep

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Magnetic small-angle neutron scattering (SANS) is a powerful technique for investigating magnetic nanoparticle assemblies in nonmagnetic matrices. For such microstructures, the standard theory of magnetic SANS assumes uniformly magnetized nanoparticles (macrospin model). However, there exist many experimental and theoretical studies which suggest that this assumption is violated: deviations from ellipsoidal particle shape, crystalline defects, or the interplay between various magnetic interactions (exchange, magnetic anisotropy, magnetostatics, external field) may lead to nonuniform spin structures. Therefore, a theoretical framework of magnetic SANS of nanoparticles needs to be developed. Here, we report numerical micromagnetic simulations of the static spin structure and related unpolarized magnetic SANS of a single cobalt nanorod. While in the saturated state the magnetic SANS cross section is (as expected) determined by the particle form factor, significant deviations appear for nonsaturated states; specifically, at remanence, domain-wall and vortex states emerge which result in a magnetic SANS signal that is composed of all three magnetization Fourier components, giving rise to a complex angular anisotropy on a two-dimensional detector. The strength of the micromagnetic simulation methodology is the possibility to decompose the cross section into the individual Fourier components, which allows one to draw important conclusions regarding the fundamentals of magnetic SANS.

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“…In Refs. [18,19], a theory of magnetic SANS based on the continuum theory of micromagnetics has been developed. The approach considers two origins of spin misalignment: (i) spatial nanometer-scale variations in the orientation and magnitude of the magnetic anisotropy field H p (r), and (ii) spatial nanometer-scale variations of the saturation magnetization M s (r).…”

Section: Theorymentioning

confidence: 99%

Magnetic small-angle neutron scattering on bulk metallic glasses: A feasibility study for imaging displacement fields

Mettus

Deckarm

Leibner

et al. 2017

Phys. Rev. Materials

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Magnetic-field-dependent small-angle neutron scattering (SANS) has been utilized to study the magnetic microstructure of bulk metallic glasses (BMGs). In particular, the magnetic scattering from soft magnetic Fe 70 Mo 5 Ni 5 P 12.5 B 2.5 C 5 and hard magnetic (Nd 60 Fe 30 Al 10 ) 92 Ni 8 alloys in the as-prepared, aged, and mechanically deformed state is compared. While the soft magnetic BMGs exhibit a large field-dependent SANS response with perturbations originating predominantly from spatially varying magnetic anisotropy fields, the SANS cross sections of the hard magnetic BMGs are only weakly dependent on the field, and their angular anisotropy indicates the presence of scattering contributions due to spatially dependent saturation magnetization. Moreover, we observe an unusual increase in the magnetization of the rare-earth-based alloy after deformation. Analysis of the SANS cross sections in terms of the correlation function of the spin misalignment reveals the existence of field-dependent anisotropic long-wavelength magnetization fluctuations on a scale of a few tens of nanometers. We also give a detailed account of how the SANS technique relates to unraveling displacement fields on a mesoscopic length scale in disordered magnetic materials.

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Effect of Dzyaloshinski-Moriya interaction on elastic small-angle neutron scattering

Cited by 26 publications

References 52 publications

Microstructural-defect-induced Dzyaloshinskii-Moriya interaction

Microstructural-defect-induced Dzyaloshinskii-Moriya interaction

Small-angle neutron scattering modeling of spin disorder in nanoparticles

Magnetic small-angle neutron scattering on bulk metallic glasses: A feasibility study for imaging displacement fields

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