Erik Brok

Erik Brok
University of Copenhagen · Niels Bohr Institute

PhD in Physics

About

22
Publications
3,274
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309
Citations
Additional affiliations
August 2010 - March 2014
Technical University of Denmark
Position
  • PhD Student

Publications

Publications (22)
Article
Full-text available
The universal theory of critical phase transitions describes the critical behavior at second-order phase transitions in infinitely large systems. With the increased contemporary interest in nanoscale materials, we investigated CoO nanoparticles by means of neutron scattering and found how the theory of critical phenomena breaks down in the nanoscal...
Preprint
Full-text available
The universal theory of critical phase transitions describes the critical behavior at second-order phase transitions in infinitely large systems. With the increased contemporary interest in nanoscale materials, we investigated CoO nanoparticles by means of neutron scattering and found how the theory of critical phenomena breaks down in the nanoscal...
Article
By combining X‐ray total scattering and small angle X‐ray scattering, it is possible to obtain unique insight into the formation of atomically precise nanoclusters. In a study of bismuth oxide clusters (DOI: 10.1002/anie.202103641), Michael Mehring, Kirsten M. Ø. Jensen et al. investigate the formation of [Bi38O45] clusters from [Bi6O8], and show t...
Article
Durch die Kombination von Röntgentotalstreuung und Röntgenkleinwinkelstreuung ist es möglich, einen einzigartigen Einblick in die Bildung von atomar präzisen Nanoclustern zu erhalten. In einer Studie über Bismutoxid‐Cluster (DOI: 10.1002/ange.202103641) untersuchen Michael Mehring, Kirsten M. Ø. Jensen et al. die Bildung von [Bi38O45]‐Clustern aus...
Article
Full-text available
The combination of in situ pair distribution function (PDF) analysis and small‐angle X‐ray scattering (SAXS) enables analysis of the formation mechanism of metal oxido nanoclusters and cluster–solvent interactions as they take place. Herein, we demonstrate the method for the formation of clusters with a [Bi38O45] core. Upon dissolution of crystalli...
Article
Skim milk concentrates have important applications in the dairy industry, often as intermediate ingredients. Concentration of skim milk by reverse osmosis membrane filtration induces water removal, which reduces the free volume between the colloidal components, in particular the casein micelles. Thermal treatment before or after concentration impac...
Article
Full-text available
The development of tools for combined, automated analysis of pair distribution function (PDF) and small-angle X-ray scattering (SAXS) data enabled the identification of intermediate species in the formation of atomically precise [Bi38O45] nanoclusters (see picture). By studying cluster–solvent interactions it was also found that the solvent can aff...
Article
By introducing hydrophilic polymers into silicone medical devices, highly beneficial biomedical properties can be realized. An established solution to introduce hydrophilic polymers is to form an interpenetrating polymer network (IPN) byperforming the hydrogel synthesis in the presence of silicone swollen in supercritical carbon dioxide. The precis...
Article
Milk is a ubiquitous foodstuff and food ingredient, and milk caseins are key to the structural properties of milk during processing and storage. Caseins self-assemble into nanometer-sized colloids, referred to as “micelles”, and particles of this size are ideally suited to study by small-angle scattering (SAS). Previous SAS measurements have almost...
Article
Full-text available
In the work reported herein, we investigate the practicality of a recently introduced variant of a general phase-sensitive method in small-angle neutron scattering that attempts to address the loss of phase-information as well as the orientational averaging simultaneously—through the use of reference structures in conjunction with finite element an...
Article
This article describes the 3D self-assembly of monodisperse colloidal magnetite nanoparticles from a dilute water-based ferrouid onto a silicon surface and the dependence of the resultant magnetic structure with applied field. The nanoparticles assemble into close-packed layers at the surface followed by more loosely-packed ones. The magnetic field...
Article
Neutron diffraction is a powerful technique for determining the magnetic structure of antiferromagnetic materials. However, for some of these, determining the detailed magnetic structure remains a challenge. In goethite (α-FeOOH) the antiferromagnetic unit cell coincides with the chemical unit cell and, consequently, nuclear and magnetic diffractio...
Article
Full-text available
Iron oxide nanoparticles are widely prevalent in our aqueous environment (e.g., streams, seawater, hydrothermal vents). Their aggregation and crystal growth depend on their chemical surroundings, for instance just a change in pH or salt concentration can greatly affect this. In turn this influences their properties, mobility, fate, and environmenta...
Article
Full-text available
The spin orientation in synthetic hematite-ilmenite samples and in a sample of natural hematite was studied from room temperature to above the antiferromagnetic-paramagnetic phase transition (the Néel temperature; TN ≈ 600-950 K) by neutron powder diffraction and at room temperature by Mössbauer spectroscopy. The usually assumed magnetic structure...
Article
The spin orientation in synthetic hematite-ilmenite samples and in a sample of natural hematite was studied from room temperature to above the antiferromagnetic-paramagnetic phase transition (the Néel temperature; $\textit{T}$$_{N}$ ≈ 600 − 950 K ) by neutron powder diffraction and at room temperature by Mö ssbauer spectroscopy. The usually assumed...
Article
In many materials it remains a challenge to reveal the nature of magnetic correlations, including antiferromagnetism and spin disorder. Revealing the spin structure in magnetic nanoparticles is further complicated by the large incoherent neutron scattering cross section from water adsorbed at the particle surfaces and by the broadening of diffracti...
Article
Full-text available
Goethite (α-FeOOH) is a common nanocrystalline antiferromagnetic mineral. However, it is typically difficult to study the properties of isolated single-crystalline goethite nanoparticles, because goethite has a strong tendency to form particles of aggregated nanograins often with low-angle grain boundaries. This nanocrystallinity leads to complex m...
Article
Large local anomalies in the Earth's magnetic field have been observed in Norway, Sweden, and Canada. These anomalies have been attributed to the unusual magnetic properties of naturally occurring hemo-ilmenite, consisting of a paramagnetic ilmenite host (α-Fe2O3-bearingFeTiO3) with exsolution lamellae (≈3μm thick) of canted antiferromagnetic hemat...
Article
Full-text available
Spin structures in nanoparticles of ferrimagnetic materials may deviate locally in a nontrivial way from ideal collinear spin structures. For instance, magnetic frustration due to the reduced numbers of magnetic neighbors at the particle surface or around defects in the interior can lead to spin canting and hence a reduced magnetization. Moreover,...
Article
We have investigated the evolution of crystal structure, cation disorder and magnetic properties of ilmenite (FeTiO3) after increasing time of high-energy ball-milling in an inert atmosphere. Refinement of X-ray diffraction data show that the hexagonal crystal structure of ilmenite is maintained after high-energy ball-milling of up to 128 h, but ne...
Article
Numerous studies of the low-temperature saturation magnetization of ferrimagnetic nanoparticles and diamagnetically substituted ferrites have shown an anomalous temperature dependence. It has been suggested that this is related to freezing of canted magnetic structures. We present models for the temperature dependence of the magnetization of a simp...
Article
We report that the spin structure of α-Fe2O3 nanoparticles rotates coherently out of the basal (001) plane at low temperatures when interacting with thin plate-shaped NiO nanoparticles. The observed spin reorientation (up to ∼70∘) in α-Fe2O3 nanoparticles has, in appearance, similarities to the Morin transition in bulk α-Fe2O3, but its origin is di...

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