Effect of annealing conditions on the microstructure and magnetic properties of sintered Nd-Fe-B magnets as seen by magnetic small-angle neutron scattering

Scientific Conference (2018, August 29)

Noncollinear magnetism in nanosized cobalt chromite

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 ▲]

Aligning self-assembled perylene bisimides in a magnetic field.

in Chemical Communications (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 ▲]

Multiple-q noncollinear magnetism in an itinerant hexagonal magnet

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 ▲]

Accessible length scale of the in-plane structure in polarized neutron off-specular and grazing-incidence small-angle scattering measurements

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 ▲]

The small-angle neutron scattering instrument D33 at the Institut Laue-Langevin

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 ▲]

Magnetische Neutronenkleinwinkelstreuung an inhomogenen Ferromagneten

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 ▲]

Theory of magnetic small-angle neutron scattering of two-phase ferromagnets

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

Magnetization reversal in Nd-Fe-B based nanocomposites as seen by magnetic small-angle neutron scattering

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 ▲]

Neutron spin-flip scattering of nanocrystalline cobalt

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