Goran Jan Nilsen

Goran Jan Nilsen
Science and Technology Facilities Council | STFC · Rutherford Appleton Laboratory

PhD

About

77
Publications
6,964
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
1,171
Citations
Additional affiliations
October 2015 - October 2018
Chalmers University of Technology
Position
  • Lecturer
September 2015 - present
Science and Technology Facilities Council
Position
  • Researcher
April 2012 - August 2015
Institut Laue-Langevin
Position
  • Instrument scientist
Description
  • Co-responsible for the D7 polarized diffuse scattering spectrometer.

Publications

Publications (77)
Preprint
We present a comprehensive experimental and ab-initio study of the $S=1/2$ Mo$^{5+}$ system, KMoOP$_2$O$_7$, and show that it realizes the $S = 1/2$ Heisenberg chain antiferromagnet model. Powder neutron diffraction reveals that KMoOP$_2$O$_7$ forms a magnetic network comprised of pairs of Mo$^{5+}$ chains within its monoclinic $P2_1/n$ structure....
Article
We introduce a simple method to extract the nuclear coherent and isotope incoherent, spin incoherent, and magnetic neutron scattering cross section components from powder scattering data measured using a single neutron beam polarization direction and a position-sensitive detector with large out-of-plane coverage. The method draws inspiration from p...
Preprint
Full-text available
The neutron diffraction and nuclear magnetic resonance (NMR) measurements have been used to microscopically analyze the magnetic structure in the $S = 1/2$ kagome antiferromagnet CdCu$_{3}$(OH)$_{6}$(NO$_{3}$)$_{2}\cdot $H$_{2}$O. Below the magnetic ordering temperature $T_N\simeq 4$ K, magnetic Bragg reflections at (110) and (100) were found in th...
Article
The realization of magnetic frustration in a metallic van der Waals (vdW) coupled material has been sought as a promising platform to explore novel phenomena, both in bulk matter and in exfoliated devices. However, a suitable material realization has been lacking so far. Here, we demonstrate that the vdW compound CeSiI hosts itinerant electrons coe...
Article
We present an experimental study of the magnetic structure and dynamics of two frustrated hyperkagome compounds, Gd3Ga5O12 and Gd3Al5O12. It has previously been shown that Gd3Ga5O12 exhibits long-range correlations of multipolar directors that are formed from antiferromagnetic spins on loops of ten ions. Using neutron diffraction and reverse Monte...
Preprint
Full-text available
The realization of magnetic frustration in a metallic van der Waals (vdW) coupled material has been sought as a promising platform to explore novel phenomena both in bulk matter and in exfoliated devices. However, a suitable material platform has been lacking so far. Here, we demonstrate that CeSiI hosts itinerant electrons coexisting with exotic m...
Article
The B-site sublattice in the double perovskite oxides A2BB'O6 (B: magnetic cation; B': nonmagnetic cation) causes spin frustration, but the relationship between the structure and spin frustration remains unclear although a number of compounds have been studied. The present study systematically investigated A2MnIIB'O6 (S = 5/2) and found that the fr...
Preprint
We present an experimental study of the magnetic structure and dynamics of two frustrated hyperkagome compounds, Gd3Ga5O12 and Gd3Al5O12. It has previously been shown that Gd3Ga5O12 exhibits long-range correlations of multipolar directors, that are formed from antiferromagnetic spins on loops of ten ions. Using neutron diffraction and Reverse Monte...
Article
We report neutron scattering and thermodynamic measurements of the quasi-one-dimensional Ising magnet SrCo2V2O8 under transverse fields along the tetragonal a/b direction. Our experiments reveal a Néel-type magnetic order in zero field, which successively changes into a coplanar antiferromagnetic order in applied fields. The detailed evolution of t...
Article
Ba2YReO6 is a double perovskite material where the Re5+ (d2) ions occupy a frustrated face-centered cubic lattice. Despite strong antiferromagnetic interactions between the Re ions, as indicated by a large negative Weiss constant θ=−616 K, spin freezing in Ba2YReO6 only occurs at 45 K. Since no long-range order of magnetic dipoles has previously be...
Article
A recent polarized neutron diffraction experiment on the 5d2 rhenium double perovskite Ba2YReO6 held at a low temperature uncovered weak magnetic diffraction peaks. Data analysis inferred a significantly reduced Re dipole moment, and long-range order compatible with an antiferromagnetic, noncollinear motif. To interpret the experimental findings, w...
Preprint
Full-text available
A recent polarized neutron diffraction experiment on the 5d2 rhenium double perovskite Ba2YReO6 held at a low temperature uncovered weak magnetic diffraction peaks. Data analysis inferred a significantly reduced Re dipole moment, and long-range order compatible with an antiferromagnet, non-collinear motif. To interpret the experimental findings, we...
Article
We report the crystal structures and magnetic properties of two pseudopolymorphs of the S=1/2 Ti3+ coordination framework, KTi(C2O4)2·xH2O. Single-crystal x-ray and powder neutron diffraction measurements on α−KTi(C2O4)2·xH2O confirm its structure in the tetragonal I4/mcm space group with a square planar arrangement of Ti3+ ions. Magnetometry and s...
Preprint
We report the crystal structures and magnetic properties of two psuedo-polymorphs of the $S=1/2$ Ti$^{3+}$ coordination framework, KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O. Single-crystal X-ray and powder neutron diffraction measurements on $\alpha$-KTi(C$_2$O$_4$)$_2\cdot$xH$_2$O confirm its structure in the tetragonal $I4/mcm$ space group with a square pl...
Article
We performed inelastic neutron scattering measurements on a polycrystalline sample of a classical kagome antiferromagnet NaBa2Mn3F11 to investigate the possibility of a dispersionless zero-energy excitation associated with rotation of spins along the chains. The observed spectra indeed exhibit such an excitation with strong intensity at low energy,...
Preprint
We performed inelastic neutron scattering measurements on a polycrystalline sample of a classical kagome antiferromagnet NaBa$_{2}$Mn$_{3}$F$_{11}$ to investigate the possibility of a dispersionless zero-energy excitation associated with rotation of spins along the chains. The observed spectra indeed exhibit such an excitation with strong intensity...
Article
Full-text available
Spin liquids are highly correlated yet disordered states formed by the entanglement of magnetic dipoles1. Theories define such states using gauge fields and deconfined quasiparticle excitations that emerge from a local constraint governing the ground state of a frustrated magnet. For example, the ‘2-in–2-out’ ice rule for dipole moments on a tetrah...
Article
Full-text available
By means of the recent implementation of neutron polarization analysis on a wide-angle time-of-flight spectrometer, we have been able to separately measure coherent and incoherent dynamic structure factors of heavy water with sub-meV resolution in a wide scattering vector (Q) range. The observed decorrelation of collective fluctuations at mesoscale...
Article
It is well established that in the low-temperature limit, the two-dimensional quantum Heisenberg antiferromagnet on a square lattice (2DQHAFSL) exhibits an anomaly in its spectrum at short-wavelengths on the zone-boundary. In the vicinity of the (π, 0) point the pole in the one-magnon response exhibits a downward dispersion, is heavily damped and a...
Article
Full-text available
We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO4)2. The magnetic susceptibility reveals strong antiferromagnetic interactions θCW=−167K and long-range magnetic order at TN=22K, in agreement with a recent report. Powder neutron diffraction further...
Preprint
Full-text available
We present an extensive experimental and theoretical study on the low-temperature magnetic properties of the monoclinic anhydrous alum compound BaMo(PO$_4$)$_2$. The magnetic susceptibility reveals strong antiferromagnetic interactions $\theta_{CW} = -167$~K and long-range magnetic order at $T_N=22$~K, in agreement with a recent report. Powder neut...
Preprint
Full-text available
It is well established that in the low-temperature limit, the two-dimensional quantum Heisenberg antiferromagnet on a square lattice (2DQHAFSL) exhibits an anomaly in its spectrum at short-wavelengths on the zone-boundary. In the vicinity of the $(\pi,0)$ point the pole in the one-magnon response exhibits a downward dispersion, is heavily damped an...
Preprint
Full-text available
Spin liquids are highly correlated yet disordered states formed by the entanglement of magnetic dipoles$^1$. Theories typically define such states using gauge fields and deconfined quasiparticle excitations that emerge from a simple rule governing the local ground state of a frustrated magnet. For example, the '2-in-2-out' ice rule for dipole momen...
Preprint
Full-text available
Terbium gallium garnet (TGG), Tb$_3$Ga$_5$O$_{12}$, is well known for its applications in laser optics, but also exhibits complex low-temperature magnetism that is not yet fully understood. Its low-temperature magnetic order is determined by means of time-of-flight neutron powder diffraction. It is found to be a multiaxial antiferromagnet with magn...
Article
The concept for a proposed upgrade to the D7 diffuse scattering spectrometer at the Institut Laue-Langevin, Grenoble, is presented. The upgrade consists of rebuilding the primary spectrometer, substantially relaxing the incident beam divergence to match the divergence that can be accepted by the secondary spectrometer. Monte-Carlo simulations and a...
Article
Full-text available
We report on the design and construction of a neutron polarization analyzer based on a ³ He spin filter for the LET spectrometer at the ISIS facility. Its commissioning completes the uniaxial polarized mode of the instrument. Besides the ³ He spin filter cell, the analyzer consists of a set of electromagnetic coils to provide a uniform magnetic fie...
Article
Terbium gallium garnet (TGG), Tb3Ga5O12, is well known for its applications in laser optics but also exhibits complex low-temperature magnetism that is not yet fully understood. Its low-temperature magnetic order is determined by means of time-of-flight neutron powder diffraction. It is found to be a multiaxial antiferromagnet with magnetic Tb3+ io...
Article
We report neutron-scattering and ac magnetic susceptibility measurements of the two-dimensional spin-1/2 frustrated magnet BaCdVO(PO4)2. At temperatures well below TN≈1K, we show that only 34% of the spin moment orders in an up-up-down-down stripe structure. Dominant magnetic diffuse scattering and comparison to published muon−spin−rotation measure...
Article
Simulated optimization of neutron instrumentation via Monte Carlo raytracing (MCR) has played a vital role in instrument design in recent decades. With the increasing complexity of modern instruments, however, optimization is becoming more computationally demanding. Graphics processing unit (GPU) acceleration is a promising strategy to reduce the h...
Preprint
Full-text available
We report neutron scattering and AC magnetic susceptibility measurements of the 2D spin-1/2 frustrated magnet BaCdVO(PO$_{4}$)$_{2}$. At temperatures well below $T_{\sf N}\approx 1K$, we show that only 34 % of the spin moment orders in an up-up-down-down strip structure. Dominant magnetic diffuse scattering and comparison to published $\mu$sr measu...
Article
Full-text available
Pyrochlore systems are ideally suited to the exploration of geometrical frustration in three dimensions, and their rich phenomenology encompasses topological order and fractional excitations. Classical spin ices provide the first context in which it is possible to control emergent magnetic monopoles, and anisotropic exchange leads to even richer be...
Article
Barlowite, Cu4(OH)6FBr, has attracted much attention as the parent compound of a new series of quantum spin-liquid candidates, ZnxCu4−x(OH)6FBr. While it is known to undergo a magnetic phase transition to a long-range ordered state at TN=15 K, there is still no consensus over either its nuclear or magnetic structures. Here, we use comprehensive, hi...
Preprint
Barlowite, Cu$_{4}$(OH)$_{6}$FBr, has attracted much attention as the parent compound of a new series of quantum spin liquid candidates, Zn$_{x}$Cu$_{4-x}$(OH)$_{6}$FBr. While it is known to undergo a magnetic phase transition to a long-range ordered state at $T_{N} = 15$ K, there is still no consensus over either its nuclear or magnetic structures...
Article
We report results from neutron diffraction with polarization analysis of the effect of In dopant level on the hydrogen concentration in hydrated samples of the proton conducting perovskite type oxide BaZr1−xInxO3−x/2 with x = 0, 0.175, 0.20, 0.225, 0.25, and 0.275. Analysis of the neutron data establishes a trend of increasing hydrogen concentratio...
Article
The A-site ordered chromate spinels LiGa1-xInxCr4O8 host a network of size-alternating spin-3/2 Cr³⁺ tetrahedra known as a "breathing" pyrochlore lattice. For the x = 0.05 composition, the complex magneto-structural ordering observed in the parent x = 0 material is replaced by a single transition at Tf = 11K, ascribed to the collinear nematic order...
Cover Page
Full-text available
Our view of proton jump diffusion in a perovskite!
Article
Acceptor-doped barium zirconates are currently receiving considerable interest because of their high proton conductivity at intermediate temperatures, making them applicable as electrolytes in various electrochemical devices, but the mechanism of proton conduction is unclear. Here, we investigate the role of the acceptor-dopant level in the localiz...
Article
The crystal structure of the mineral boleite contains clusters of 24 S=1/2Cu2+ ions that have the shape of a truncated cube formed of eight trimers connected by edges. Susceptibility measurements and exact diagonalization calculations suggest that there are strong antiferromagnetic intratrimer interactions, such that effective S=1/2 degrees of free...
Article
The combination of neutron time-of-flight spectroscopy and longitudinal polarization analysis opens up the possibility of simultaneously separating cross-section components over vast regions in (Q,ΔE) space. In this paper, we describe initial results of a project to install longitudinal polarization analysis on the LET cold neutron spectrometer at...
Article
Full-text available
The charge ordered structure of ions and vacancies characterizing rare-earth pyrochlore oxides serves as a model for the study of geometrically frustrated magnetism. The organization of magnetic ions into networks of corner-sharing tetrahedra gives rise to highly correlated magnetic phases with strong fluctuations, including spin liquids and spin i...
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
We present time-of-flight neutron total scattering and polarized neutron scattering measurements of the magnetically frustrated compounds NaCaCo$_2$F$_7$ and NaSrCo$_2$F$_7$, which belong to a class of recently discovered pyrochlore compounds based on transition metals and fluorine. The magnetic pair distribution function (mPDF) technique is used t...
Article
We present the results of a combined $^7$Li NMR and diffraction study on LiGa$_{0.95}$In$_{0.05}$Cr$_4$O$_8$, a member of LiGa$_{1-x}$In$_{x}$Cr$_4$O$_8$ "breathing" pyrochlore family. Via specific heat and NMR measurements, we find that the complex sequence of first-order transitions observed for $x=0$ is replaced by a single, apparently second-or...
Article
Full-text available
We present a design for implementing uniaxial polarisation analysis on the LET cold neutron time-of-flight spectrometer, installed on the second target station at ISIS. The polarised neutron beam is to be produced by a transmission-based supermirror polariser with the polarising mirrors arranged in a "double-V" formation. This will be followed by a...
Article
The instrumental divergence parameters and resolution for the D7 neutron diffuse scattering spectrometer at the Institut Laue-Langevin, France, are presented. The resolution parameters are calibrated against measurements of powders, single crystals, and the incoherent scattering from vanadium. We find that the powder diffraction resolution is well...
Article
The layered compound KCu$_3$As$_2$O$_7$(OD)$_3$, comprising distorted kagome planes of $S=1/2$ Cu$^{2+}$ ions, is a recent addition to the family of type-II multiferroics. Previous zero field neutron diffraction work has found two helically ordered regimes in \kns, each showing a distinct coupling between the magnetic and ferroelectric order parame...
Article
Full-text available
Magnetic frustration and low dimensionality can prevent long range magnetic order and lead to exotic correlated ground states. SrDy$_2$O$_4$ consists of magnetic Dy$^{3+}$ ions forming magnetically frustrated zig-zag chains along the c-axis and shows no long range order to temperatures as low as $T=60$ mK. We carried out neutron scattering and AC m...
Article
We show that the observed ferromagnetic behavior of ZnO lightly doped with Mn coincides with the presence of MnO nanoparticles, whereas cluster-free Mn doped ZnO behaves paramagnetically. This conclusion is reached by a study of the structural and magnetic properties of powdered samples of (Mnx,Zn1–x)O with x ≤ 0.033 using polarized neutron scatter...
Article
Hydrated samples of the two proton conducting perovskites BaZr0.9M0.1O2.95 (M = Y and Sc) were investigated using neutron spin-echo spectroscopy together with thermal gravimetric measurements, polarized neutron diffraction, and infrared spectroscopy, with the aim to determine how the atomic-scale proton dynamics depend on temperature, and type of d...
Article
Full-text available
The anhydrous alum KTi(SO4)(2), where the Ti3+ (d(1), S = 1/2) ions form an anisotropic triangular lattice, has been prepared by a new hydrothermal route and characterized by magnetic susceptibility and neutron scattering measurements. Contrary to expectations, fits to the magnetic susceptibility indicate that the spins are isotropic (i.e. Heisenbe...
Article
Full-text available
We present a neutron scattering study of the chromate spinel LiInCr4O8, which realizes a "breathing" pyrochlore lattice of S=32 spins. High-resolution neutron diffraction reveals a phase separation into a mixture of minority cubic and majority tetragonal phases below 18 K, followed by apparent magnetic order in a complex two-up two-down pattern in...
Article
Full-text available
The spinel oxides LiGaCr4O8 and LiInCr4O8 contain size-alternating pyrochlore lattices of spin-3/2 Cr3+ tetrahedra with different magnitudes of alternation. We show here that the solid solutions LiGa1-xInxCr4O8 between these two 'breathing' pyrochlore compounds display (i) rapid suppression of magnetic and structural transitions upon doping the end...
Article
Full-text available
Diffuse magnetic scattering in the highly frustrated double perovskite ${\text{Ba}}_{2}{\text{YRuO}}_{6}$ was investigated using polarized neutrons. Consistent with previous reports, the material shows two apparent transitions at 47 and 36 K to an eventual type I face-centered-cubic magnetic ground state. The (100) magnetic reflection shows differe...
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
The square-lattice quantum Heisenberg antiferromagnet displays a pronounced anomaly of unknown origin in its magnetic excitation spectrum. The anomaly manifests itself only for short wavelength excitations propagating along the direction connecting nearest neighbors. Using polarized neutron spectroscopy, we have fully characterized the magnetic flu...
Article
Full-text available
We present new magnetic heat capacity and neutron scattering results for two magnetically frustrated molybdate pyrochlores: $S=1$ oxide Lu$_2$Mo$_2$O$_7$ and $S={\frac{1}{2}}$ oxynitride Lu$_2$Mo$_2$O$_5$N$_2$. Lu$_2$Mo$_2$O$_7$ undergoes a transition to an unconventional spin glass ground state at $T_f {\sim} 16$ K. However, the preparation of the...
Article
Full-text available
Several Cu$^{2+}$ hydroxide minerals have recently been identified as candidate realizations of the $S=1/2$ kagome Heisenberg model. In this context, we have studied the distorted system KCu$_3$As$_2$O$_7$(OD)$_3$ using neutron scattering and bulk measurements. Although the distortion favors magnetic order over a spin liquid ground state, refinemen...
Article
Full-text available
The compound KTi(SO4)2.H2O was recently reported as a quasi one-dimensional spin 1/2 compound with competing antiferromagnetic nearest neighbor exchange J1 and next-nearest neighbor exchange J2 along the chain with a frustration ratio alpha = J2/J1 ~ 0.29 [Chem. Mater. vol. 20, pg. 8 (2008)]. Here, we report a microscopically based magnetic model f...
Article
Full-text available
A unique type of frustrated lattice is found in two A-site ordered spinel oxides, LiGaCr_{4}O_{8} and LiInCr_{4}O_{8}. Because of the large size mismatch between Li^{+} and Ga^{3+}/In^{3+} ions at the A site, the pyrochlore lattice, made up of Cr^{3+} ions carrying spin 3/2, becomes an alternating array of small and large tetrahedra, i.e., a "breat...
Article
The low-energy (ϵ = ħω < 1 meV), low-temperature (T = 0.05 K) spin dynamics of the s = 1/2 kagome candidate herbertsmithite are probed in the presence of magnetic fields up to 2.5 T. The zero-field spectra reveal a very weak continuum of scattering at T = 10 K and a broad inelastic peak centred at ϵ(max) = 0.2 meV at lower temperatures, T < 1 K. Th...