References of "Honecker, Dirk 50035792"
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See detailRelating Magnetic Properties and High Hyperthermia Performance of Iron Oxide Nanoflowers
Bender, Philipp Florian UL; Fock, Jeppe; Frandsen, Cathrine et al

in JOURNAL OF PHYSICAL CHEMISTRY C (2018), 122(5), 3068-3077

We investigated, in depth, the interrelations among structure, magnetic properties, relaxation dynamics and magnetic hyperthermia performance of magnetic nanoflowers. The nanoflowers are about 39 nm in ... [more ▼]

We investigated, in depth, the interrelations among structure, magnetic properties, relaxation dynamics and magnetic hyperthermia performance of magnetic nanoflowers. The nanoflowers are about 39 nm in size, and consist of densely packed iron oxide cores. They display a remanent magnetization, which we explain by the exchange coupling between the cores, but we observe indications for internal spin disorder. By polarized small-angle neutron scattering, we unambiguously confirm that, on average, the nanoflowers are preferentially magnetized along one direction. The extracted discrete relaxation time distribution of the colloidally dispersed particles indicates the presence of three distinct relaxation contributions. We can explain the two slower processes by Brownian and classical Néel relaxation, respectively. The additionally observed very fast relaxation contributions are attributed by us to the relaxation of disordered spins within the nanoflowers. Finally, we show that the intrinsic loss power (ILP, magnetic hyperthermia performance) of the nanoflowers measured in colloidal dispersion at high frequency is comparatively large and independent of the viscosity of the surrounding medium. This concurs with our assumption that the observed relaxation in the high frequency range is primarily a result of internal spin relaxation, and possibly connected to the disordered spins within the individual nanoflowers. [less ▲]

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See detailDirect evidence for cycloidal modulations in the thermal-fluctuation-stabilized spin spiral and skyrmion states of GaV 4 S 8
White, J. S.; Butykai, A.; Cubitt, R. et al

in Physical Review. B (2018), 97(2), 020401

We report small-angle neutron scattering studies of the lacunar spinelGaV4S8,which reveal the long-wavelength <br />magnetic phases to be cycloidally modulated. Upon cooling, these modulated phases ... [more ▼]

We report small-angle neutron scattering studies of the lacunar spinelGaV4S8,which reveal the long-wavelength <br />magnetic phases to be cycloidally modulated. Upon cooling, these modulated phases, including a recently <br />proposed Néel-type skyrmion phase, transform into a simple ferromagnetic state. These results indicate the <br />modulated phases in GaV4S8 gain their stability from thermal fluctuations, while at lower temperatures the <br />ferromagnetic state emerges in accord with the strong easy-axis magnetic anisotropy. Crucially, our study provides <br />microscopic evidence that the skyrmions in GaV4S8 indeed display a Néel-type helicity. More generally, our <br />approach can be applied to evidence the helicity of any bulk skyrmion phase. [less ▲]

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See detailAligning self-assembled perylene bisimides in a magnetic field.
Draper, Emily R.; Wallace, Matthew; Honecker, Dirk UL et al

in Chemical communications (Cambridge, England) (2018), 54(78), 10977-10980

Photoconductive self-assembled 1D structures can be formed by perylene bisimides. These structures are generally randomly orientated, limiting their applications as conductive wires. Here, we show that ... [more ▼]

Photoconductive self-assembled 1D structures can be formed by perylene bisimides. These structures are generally randomly orientated, limiting their applications as conductive wires. Here, we show that magnetic fields can be used to create highly aligned, directionally-dependent thin films. This approach leads to well-aligned structures over large areas. [less ▲]

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See detailNoncollinear magnetism in nanosized cobalt chromite
Zakutna, D.; Vlcek, J.; Fitl, P. et al

in PHYSICAL REVIEW B (2018), 98(6), 064407

Using a combination of neutron diffraction with XYZ polarization analysis and magnetization measurements, the noncollinear magnetism in nanosized cobalt chromite, a potential multiferroic material, is ... [more ▼]

Using a combination of neutron diffraction with XYZ polarization analysis and magnetization measurements, the noncollinear magnetism in nanosized cobalt chromite, a potential multiferroic material, is revealed. For noninteracting 26.9(1) nm nanoparticles, a bulklike behavior is identified, including a ferrimagnetic Curie temperature of 99 K and a transition to the spin spiral magnetic phase at 27 K with a temperature-dependent, incommensurate propagation vector. A lock-in transition towards a commensurate propagation vector is not observed. Much smaller, 3.1(2) nm, nanoparticles reveal a strong cluster glass behavior, characterized by ferrimagnetic behavior below the Curie temperature of 43 K and a transition to asperomagnetic behavior at 18 K, with the absence of any magnetic reflections at a base temperature of 5 K. [less ▲]

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See detailMultiple-q noncollinear magnetism in an itinerant hexagonal magnet
Takagi, R.; White, J. S.; Hayami, S. et al

in SCIENCE ADVANCES (2018), 4(11),

rticle Figures & Data Info & Metrics eLetters PDF Abstract Multiple-q spin order, i.e., a spin texture characterized by a multiple number of coexisting magnetic modulation vectors q, has recently ... [more ▼]

rticle Figures & Data Info & Metrics eLetters PDF Abstract Multiple-q spin order, i.e., a spin texture characterized by a multiple number of coexisting magnetic modulation vectors q, has recently attracted attention as a source of nontrivial magnetic topology and associated emergent phenomena. One typical example is the triple-q skyrmion lattice state stabilized by Dzyaloshinskii-Moriya interactions in noncentrosymmetric magnets, while the emergence of various multiple-q states of different origins is expected according to the latest theories. Here, we investigated the magnetic structure of the itinerant polar hexagonal magnet Y3Co8Sn4, in which several distinctive mechanisms favoring multiple-q states are allowed to become active. Small-angle neutron-scattering experiments suggest the formation of incommensurate triple-q magnetic order with an in-plane vortex-like spin texture, which can be most consistently explained in terms of the novel four-spin interaction mechanism inherent to itinerant magnets. The present results suggest a new route to realizing exotic multiple-q orders and that itinerant hexagonal magnets, including the R3M8Sn4 family with wide chemical tunability, can be a unique material platform to explore their rich phase diagrams. [less ▲]

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See detailTransparent-to-dark photo- and electrochromic gels
Gonzalez, Laura; Liu, Chung; Dietrich, Bart et al

in COMMUNICATIONS CHEMISTRY (2018), 1

Smart windows in which the transmittance can be controlled on demand are a promising solution for the reduction of energy use in buildings. Windows are often the most energy inefficient part of a building ... [more ▼]

Smart windows in which the transmittance can be controlled on demand are a promising solution for the reduction of energy use in buildings. Windows are often the most energy inefficient part of a building, and so controlling the transmittance has the potential to significantly improve heating costs. Whilst numerous approaches exist, many suitable materials are costly to manufacture and process and so new materials could have a significant impact. Here we describe a gel-based device which is both photo- and electrochromic. The gel matrix is formed by the self-assembly of a naphthalene diimide. The radical anion of the naphthalene diimide can be formed photo or electrochemically, and leads to a desirable transition from transparent to black. The speed of response, low potential needed to generate the radical anion, cyclability of the system, temperature stability and low cost mean these devices may be suitable for applications in smart windows. [less ▲]

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See detailDipolar-coupled moment correlations in clusters of magnetic nanoparticles
Bender, Philipp Florian UL; Wetterskog, E.; Honecker, Dirk UL et al

in Physical Review. B, Condensed Matter (2018), 98

Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid–coated magnetic <br />nanoparticles. The individual iron oxide cores were composed of >95% maghemite and ... [more ▼]

Here, we resolve the nature of the moment coupling between 10-nm dimercaptosuccinic acid–coated magnetic <br />nanoparticles. The individual iron oxide cores were composed of >95% maghemite and agglomerated to <br />clusters. At room temperature the ensemble behaved as a superparamagnet according to Mössbauer and magnetization <br />measurements, however, with clear signs of dipolar interactions. Analysis of temperature-dependent <br />ac susceptibility data in the superparamagnetic regime indicates a tendency for dipolar-coupled anticorrelations <br />of the core moments within the clusters. To resolve the directional correlations between the particle moments <br />we performed polarized small-angle neutron scattering and determined the magnetic spin-flip cross section <br />of the powder in low magnetic field at 300 K. We extract the underlying magnetic correlation function of <br />the magnetization vector field by an indirect Fourier transform of the cross section. The correlation function <br />suggests nonstochastic preferential alignment between neighboring moments despite thermal fluctuations, with <br />anticorrelations clearly dominating for next-nearest moments. These tendencies are confirmed by Monte Carlo <br />simulations of such core clusters. [less ▲]

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See detailSpin-wave dynamics in the helimagnet FeGe studied by small-angle neutron scattering
Siegfried, S.-A.; Sukhanov, A. S.; Altynbaev, E. V. et al

in PHYSICAL REVIEW B (2017), 95(13), 134415

We have studied the spin-wave stiffness of the Dzyaloshinskii-Moriya helimagnet FeGe in a temperature range from 225 K up to TC ≈ 278.7 K by small-angle neutron scattering. The method we have used is ... [more ▼]

We have studied the spin-wave stiffness of the Dzyaloshinskii-Moriya helimagnet FeGe in a temperature range from 225 K up to TC ≈ 278.7 K by small-angle neutron scattering. The method we have used is based on [Grigoriev et al., Phys. Rev. B 92, 220415(R) (2015)] and was extended here for the application in polycrystalline samples. We confirm the validity of the anisotropic spin-wave dispersion for FeGe caused by the Dzyaloshinskii-Moriya interaction. We have shown that the spin-wave stiffness A for the FeGe helimagnet decreases with a temperature as A(T ) = 194[1 − 0.7(T/TC)4.2] meV °A2. The finite value of the spin-wave stiffness A = 58 meV °A2 at TC classifies the order-disorder phase transition in FeGe as being the first-order one. [less ▲]

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See detailAccessible length scale of the in-plane structure in polarized neutron off-specular and grazing-incidence small-angle scattering measurements
Maruyama, R.; Bigault, T.; Wildes, A. R. et al

in Journal of Physics Conference Series (2017), 862

Polarized neutron off-specular and grazing-incidence small-angle scattering measurements are useful methods to investigate the in-plane structure and its correlation of layered systems. Although these ... [more ▼]

Polarized neutron off-specular and grazing-incidence small-angle scattering measurements are useful methods to investigate the in-plane structure and its correlation of layered systems. Although these measurements give information on complementary and overlapping length scale, the different characteristics between them need to be taken into account when performed. In this study, the difference in the accessible length scale of the in-plane structure, which is one of the most important characteristics, was discussed using an Fe/Si multilayer together with simulations based on the distorted wave Born approximation. [less ▲]

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See detailThe small-angle neutron scattering instrument D33 at the Institut Laue-Langevin
Dewhurst, C. D.; Grillo, I.; Honecker, Dirk UL et al

in JOURNAL OF APPLIED CRYSTALLOGRAPHY (2016), 49

The D33 small-angle neutron scattering (SANS) instrument at the Institut Laue–Langevin (ILL) is the most recent SANS instrument to be built at the ILL. In a project beginning in 2005 and lasting seven ... [more ▼]

The D33 small-angle neutron scattering (SANS) instrument at the Institut Laue–Langevin (ILL) is the most recent SANS instrument to be built at the ILL. In a project beginning in 2005 and lasting seven years, the concept has been developed, and the instrument designed, manufactured and installed. D33 was commissioned with neutrons during the second half of 2012, fully entering the ILL user programme in 2013. The scientific case required that D33 should provide a wide dynamic range of measured scattering vector magnitude q, flexibility with regard to the instrument resolution, and the provision of polarized neutrons and 3He spin analysis to facilitate and expand studies in magnetism. In monochromatic mode, a velocity selector and a flexible system of inter-collimation apertures define the neutron beam. A double-chopper system enables a time-of-flight (TOF) mode of operation, allowing an enhanced dynamic q range (qmax/qmin) and a flexible wavelength resolution. Two large multitube detectors extend the dynamic q range further, giving qmax/qmin ’ 25 in monochromatic mode and a very large qmax/qmin > 1000 in TOF mode. The sample zone is large and flexible in configuration, accommodating complex and bulky sample environments, while the position of D33 is such as to allow high magnetic fields at the sample position. The instrument is of general purpose with a performance rivalling that of D22, and is well adapted for SANS studies in scientific disciplines as diverse as solution scattering in biology and soft matter and studies of physics, materials science and magnetism. This article provides a detailed technical description of D33 and its performance and characterization of the individual components, and serves as a technical reference for users of the instrument. [less ▲]

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See detailExcitation of Ni nanorod colloids in oscillating magnetic fields: a new approach for nanosensing investigated by TISANE
Bender, Philipp; Günther, Annegret UL; Honecker, Dirk UL et al

in Nanoscale (2015), 7

The response of a colloidal dispersion of Ni nanorods to an oscillating magnetic field was characterized by optical transmission measurements as well as small-angle neutron scattering (SANS) experiments ... [more ▼]

The response of a colloidal dispersion of Ni nanorods to an oscillating magnetic field was characterized by optical transmission measurements as well as small-angle neutron scattering (SANS) experiments using the TISANE (Time-dependent SANS experiments) technique. Exposed to a static magnetic field, the scattering intensity of the rod ensemble could be well described by the cylinder form factor using the geometrical particle parameters (length, diameter, orientation distribution) determined by transmission electronmicroscopy and magnetometry. An oscillation of the field vector resulted in a reorientation of the nanorods and a time-dependency of the scattering intensity due to the shape anisotropy of the rods. Analysis of the SANS data revealed that in the range of low frequencies the orientation distribution of the rods is comparable to the static case. With increasing frequency, the rod oscillation was gradually damped due to an increase of the viscous drag. It could be shown that despite of the increased friction in the high frequency range no observable change of the orientation distribution of the ensemble with respect to its symmetry axis occurs. [less ▲]

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See detailMagnetische Neutronenkleinwinkelstreuung an inhomogenen Ferromagneten
Honecker, Dirk UL

Doctoral thesis (2014)

Small-angle neutron scattering (SANS) is a powerful method to investigate the magnetic microstructure in the bulk and on length scales between about 1 − 100 nm. SANS experiments are commonly realized with ... [more ▼]

Small-angle neutron scattering (SANS) is a powerful method to investigate the magnetic microstructure in the bulk and on length scales between about 1 − 100 nm. SANS experiments are commonly realized with an unpolarised or a polarised incident neutron beam, however, an analysis of the neutron spin state after the scattering process is usually not performed. As a result of the development of efficient 3He spin filters, a so-called longitudinal (one-dimensional) neutron-polarization analysis (POLARIS) at SANS instruments is now routinely available. The analysis of POLARIS data allows one to extract the Fourier components of the magnetization vector field. Experimental results on Fe-based two-phase nanocrystalline alloys serve as examples in order to demonstrate the capabilities of the POLARIS technique. In the investigated soft magnetic heterogeneous nanocomposites, the jump of the magnetization at the phase boundary between particles and matrix gives rise to a magnetostatic stray field, which represents a non-negligible source of spin disorder. As one of the central results of this dissertation, an analytical micromagnetic theory is presented, which allows one to analyze the magnetic-field-dependent SANS cross section of such particle-matrix-type ferromagnets. It is shown that the magnetic anisotropy field and the magnetostatic field decisively determine the properties of the magnetic SANS cross section, such as the asymptotic power-law behaviour, the range of spin-misalignment correlations and angular anisotropies. In particular, the theory explains the “clover-leaf”-shaped angular anisotropy, which is observed for several nanostructured magnetic materials and which can be attributed to jumps of the magnetization at internal interfaces. The micromagnetic aproach allows one to specify the field behaviour of the magnetic SANS and to quantitatively assess substantial features of the spin structure, for instance, the average exchange-stiffness constant and the mean magnetic anisotropy and magnetostatic fields. [less ▲]

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See detailTheory of magnetic small-angle neutron scattering of two-phase ferromagnets
Honecker, Dirk UL; Michels, Andreas UL

in Physical Review. B, Condensed Matter and Materials Physics (2013), 87(224426), 1-10

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See detailAnalysis of magnetic neutron-scattering data of two-phase ferromagnets
Honecker, Dirk UL; Dewhurst, Charles; Suzuki, Kiyonori et al

in Physical Review. B, Condensed Matter and Materials Physics (2013), 88

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See detailMagnetization reversal in Nd-Fe-B based nanocomposites as seen by magnetic small-angle neutron scattering
Bick, Jens-Peter UL; Honecker, Dirk UL; Döbrich, Frank UL et al

in Applied Physics Letters (2013), 102(2), 0224151-0224155

We have studied the magnetization-reversal process of a Nd2Fe14B/Fe3B nanocomposite using small-angle neutron scattering. Based on the computation of the autocorrelation function of the spin misalignment ... [more ▼]

We have studied the magnetization-reversal process of a Nd2Fe14B/Fe3B nanocomposite using small-angle neutron scattering. Based on the computation of the autocorrelation function of the spin misalignment, we have estimated the characteristic size lC of spin inhomogeneities around the Nd2Fe14B nanoparticles. The quantity lC approaches a constant value of about 12.5 nm ( ∼ average Nd2Fe14B particle radius) at 14 T and takes on a maximum value of about 18.5 nm at the coercive field of −0.55 T. The field dependence of lC can be described by a model that takes into account the convolution relationship between the nuclear and the magnetic microstructure. [less ▲]

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See detailObservation of cross-shaped anisotropy in spin-resolved small-angle neutron scattering
Michels, Andreas UL; Honecker, Dirk UL; Döbrich, Frank UL et al

in Physical Review. B, Condensed Matter and Materials Physics (2012), 85(184417), 1-5

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See detailNeutron spin-flip scattering of nanocrystalline cobalt
Honecker, Dirk UL; Döbrich, Frank UL; Dewhurst, C. D. et al

in Journal of Physics : Condensed Matter (2011), 23(1), 1-4

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See detailSmall-angle Neutron Scattering with One-dimensional Polarization Analysis
Michels, Andreas UL; Honecker, Dirk UL; Döbrich, Frank UL et al

in Neutron News (2011), 22(3), 15-19

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See detailNeutron spin-flip scattering of nanocrystalline cobalt
Honecker, Dirk UL; Döbrich, Frank; Dewhurst, C. D. et al

in Journal of Physics: Condensed Matter (2010), 23(1), 016003

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