Three-dimensional Magnetization Research Articles

Three-dimensional magnetization reconstruction from electron optical phase images with physical constraints

The ability to characterize three-dimensional (3D) magnetization distributions in nanoscale magnetic materials and devices is essential to fully understand their static and dynamic magnetic properties. Phase contrast techniques in the transmission electron microscope (TEM), such as electron holography and electron ptychography, can be used to record two-dimensional (2D) projections of the in-plane magnetic induction of 3D nanoscale objects. Although the 3D magnetic induction can in principle be reconstructed from one or more tilt series of such 2D projections, conventional tomographic reconstruction algorithms do not recover the 3D magnetization within a sample directly. Here, we use simulations to describe the basis of an improved model-based algorithm for the tomographic reconstruction of a 3D magnetization distribution from one or more tilt series of electron optical phase images recorded in the TEM. The algorithm allows a wide range of physical constraints, including a priori information about the sample geometry and magnetic parameters, to be specified. It also makes use of minimization of the micromagnetic energy in the loss function. We demonstrate the reconstruction of the 3D magnetization of a localized magnetic soliton — a hopfion ring — and discuss the influence of noise, choice of magnetic constants, maximum tilt angle and number of tilt axes on the result. The algorithm can in principle be adapted for other magnetic contrast imaging techniques in the TEM, as well as for other magnetic characterization techniques, such as those based on X-rays or neutrons.

MRI AND BLOOD-BASED BIOMARKERS ASSOCIATED WITH SURGICAL MANAGEMENT IN CHILDREN AND ADULTS WITH SMALL BOWEL CROHN'S DISEASE

Abstract BACKGROUND Despite advances in medical therapy, many children and adults with ileal Crohn’s Disease (CD) progress to fibrostenosis requiring surgery. Prior studies have identified circulating and imaging biomarkers associated with strictures, although their associations with need for surgery are not well-established. PURPOSE We aimed to identify MRI and circulating biomarkers associated with the need for surgical management in chidlren and adults with ileal CD. METHODS This prospective, multi-center study included pediatric and adult CD cases undergoing ileal resection (n=50), and CD controls receiving medical therapy (n=83). Noncontrast research MRI examinations measured bowel wall three-dimensional magnetization transfer ratio normalized to skeletal muscle (normalized 3D MTR), modified Look-Locker inversion recovery (MOLLI) T1 relaxation, intravoxel incoherent motion (IVIM) diffusion-weighted imaging metrics, and the simplified magnetic resonance index of activity (sMaRIA) (Figure 1). Circulating biomarkers included CD64, ECM1, and GM-CSF autoantibodies (Ab). Clinical variables, including demographics, anthropometrics, and routine clinical laboratory data (e.g., CRP, fecal calprotectin), also were obtained at the research visit. Associations between MRI and circulating biomarkers and need for ileal resection were tested using univariate and multivariable LASSO regression. RESULTS Mean participant age was 23.9±13.1 years. Disease duration and treatment exposures did not vary between the groups. Univariate biomarker associations with ileal resection included log GM-CSF Ab (odds ratio [OR]=2.87; p=0.0009), normalized 3D MTR (OR=1.05; p=0.002), log MOLLI T1 (OR=0.01; p=0.02), log IVIM perfusion fraction (f) (OR=0.38; p=0.04), and IVIM apparent diffusion coefficient (ADC) (OR=0.3; p=0.001). MRI and circulating biomarker Tukey box plots are presented in Figure 2. The multivariable model for surgery based upon AICc criteria included age (OR=1.03; p=0.29), BMI (OR=0.91; p=0.09), log GM-CSF Ab (OR=3.37; p=0.01), normalized 3D MTR (OR=1.07; p=0.007), sMaRIA (OR=1.14; p=0.61), luminal narrowing (OR=10.19; p=0.003), log CRP (normalized) (OR=2.75; p=0.10), and hematocrit (OR=0.90; p=0.13). CONCLUSION After accounting for clinical and MRI measures of severity, normalized 3D MTR and GM-CSF Ab are associated with need for surgery in ileal CD. GM-CSF autoantibodies and MRI biomarker sequences may be useful for guiding management decisions in CD patients. Figure 1 Research MRI images from a surgical Crohn’s disease patient with stricturing behavior involving the terminal ileum. A and B. Coronal and axial fat-saturated T2-weighted single-shot fast spin-echo (SSFSE) images show wall thickening and luminal narrowing of the terminal ileum (arrows) with more proximal bowel dilation measuring greater than 3 cm. C. Axial 3D magnetization transfer images – MT pulse on (bottom image, arrow), MT pulse off (top image, arrow). D. Axial modified Look-Locker inversion recovery (MOLLI) T1 relaxation image (arrow). E. Representative axial intravoxel incoherent motion diffusion-weighted images with increasing b-values (left to right, arrows). Figure 2 Variation in circulating and imaging biomarkers in Crohn’s disease patients with medical and surgical management. Ctrl: non-IBD healthy controls; Med: CD patients with nonsurgical medical management; Surg: CD patients with surgical management.

BORIS – Micromagnetic, Spin Transport and Multiscale Atomistic Software for Modelling Magnetic Information Storage

A brief review of BORIS is given here, together with a review of recent works using this software, including applications to modelling magnetic hard-disk-drive read heads, ultrafast magnetization processes, computation of thermodynamic equilibrium states using Monte Carlo algorithms, and modelling skyrmions as information carriers. BORIS is a state-of-the-art multi-physics and multi-scale research software designed to solve three-dimensional magnetization dynamics problems, coupled with a self-consistent charge and spin transport solver, heat flow solver with temperature-dependent material parameters, and elastodynamics solver including thermoelastic and magnetoelastic/magnetostriction effects, in arbitrary multi-layered structures and shapes. Both micromagnetic and atomistic models are implemented, also allowing multi-scale modelling where computational spaces may be configured with multiple simultaneous micromagnetic and atomistic discretization regions. The software allows multi-GPU computations on any number of GPUs in parallel, in order to accelerate simulations and allow for larger problem sizes compared to single-GPU computations – this is the first magnetization dynamics software to allow multi-GPU computations, enabling large problems encompassing billions of cells to be simulated with unprecedented performance.

A Potential Mechanism of Neurological Impairment in Children With Infantile Spasm: Based on Microanatomic Structure Analysis Employing Voxel-Based Morphometry and Surface-Based Morphometry

BackgroundInfantile epileptic spasms syndrome (IESS) would accompany with severe neurological impairment. Our study aimed to explore the potential mechanism by employing voxel-based and surface-based morphometry to detect brain microwould accompany with severe neurological impairment. Our study aimed to explore the potential mechanism by employing voxel-based and surface-based morphometry to detect brain microanatomic structure alteration. MethodsThe IESS group had 21 males and 13 females (mean age: 17.7 ± 15.6 months), whereas the healthy controls group had 22 males and 10 females (mean age: 29.4 ± 18.7 months). High-resolution 3D T1WI was performed. Computational Anatomy Toolbox implemented in Statistical Parametric Mapping 12 was used to measure the gray matter and white matter volume, and the cortical thickness separately. Independent sample t test was used to assess between-group differences. IESS group was assessed using the Bayley Scales of Infant Development. ResultsThe IESS group showed a significantly decreased volume of gray matter in right middle temporal gyrus, inferior temporal gyrus, superior temporal gyrus, right fusiform, and bilateral precuneus (P < 0.001). There were no significant between-group differences with respect to white matter volume or cortical thickness (P > 0.001). The results of Bayley Scales of Infant Development showed that the Mental Development Index (MDI) and Psychomotor Development Index scores of children with IESS were almost concentrated in the range of <70. MDI score showed a positive correlation with gray matter reduction area in IESS group. ConclusionChildren with IESS had impaired cognitive and delayed motor development. And the decreased gray matter in the right temporal lobe, fusiform, and bilateral precuneus could be the potential anatomic basis for impaired function, such as hearing, visual, and language.

Analysis of morphological and quantitative changes in pathological myopia and perioperative changes in posterior scleral reinforcement using three-dimensional magnet resonance imaging.

Objective: To compare the morphological and quantitative changes in pathological myopia (PM) and the perioperative changes in posterior scleral reinforcement (PSR) using three-dimensional magnetic resonance images (3D MRI). Methods: A total of 49 patients with high myopia (HM; 98 eyes), 15 with pathological myopia (PM; 19 eyes), and 10 without high myopia (NORM; 20 eyes) were recruited between September 2019 and July 2021. The patients underwent measurements of refractive error and axial length, as well as 3D MRI of the eyeball. Python was used to analyze the 3D MRI images, calculate the vitreous volume, establish a topography of the height of the eyeball posterior surface, and calculate the rate of change in height (H). For the PM group undergoing PSR, changes in vitreous volume and the highest point of the eyeball posterior surface in four quadrants (temporal, subtemporal, nasal, and subnasal) were compared before and after PSR. Results: The vitreous volume was smaller in the NORM group compared to the HM and PM groups (p < 0.01). The PM group had a larger volume than the HM group (p < 0.01). The H for the PM group was higher than that of the NORM and HM groups (p < 0.01). After PSR in the PM group, the total vitreous volume, as well as the volume in the subnasal and supratemporal quadrants, decreased (p < 0.05). Additionally, the highest point of the eyeball's posterior surface was generally shifted to the upper nasal side. Finally, the shape and position of the scleral band after PSR were plotted. Conclusion: 3D MRI is capable of a quantitative description of the eyeball morphology in PM and PSR. It allows for precise calculations of changes in vitreous volume and the H of the posterior surface. It also facilitates a meticulous analysis of the specific details of the scleral band following PSR.

Hopfion rings in a cubic chiral magnet

Magnetic skyrmions and hopfions are topological solitons1—well-localized field configurations that have gained considerable attention over the past decade owing to their unique particle-like properties, which make them promising objects for spintronic applications. Skyrmions2,3 are two-dimensional solitons resembling vortex-like string structures that can penetrate an entire sample. Hopfions4–9 are three-dimensional solitons confined within a magnetic sample volume and can be considered as closed twisted skyrmion strings that take the shape of a ring in the simplest case. Despite extensive research on magnetic skyrmions, the direct observation of magnetic hopfions is challenging10 and has only been reported in a synthetic material11. Here we present direct observations of hopfions in crystals. In our experiment, we use transmission electron microscopy to observe hopfions forming coupled states with skyrmion strings in B20-type FeGe plates. We provide a protocol for nucleating such hopfion rings, which we verify using Lorentz imaging and electron holography. Our results are highly reproducible and in full agreement with micromagnetic simulations. We provide a unified skyrmion–hopfion homotopy classification and offer insight into the diversity of topological solitons in three-dimensional chiral magnets.

Numerical study of two-terminal SOT-MRAM

A fully three-dimensional model coupling charge, spin, magnetization, and temperature dynamics is employed to study the switching behavior of the two-terminal spin–orbit torque magnetoresistive random access memory (2T-SOT-MRAM). We demonstrated that free layer (FL) spin-transfer torque (STT) switching is strongly affected by the inclusion of the SOT. The nucleation of the FL magnetization reversal is similar to the conventional three-terminal (3T)-SOT-MRAM. In comparison to the traditional STT-MRAM, the switching times and critical switching voltages are considerably reduced. Furthermore, the full thermal simulations show the significance of the heating process and temperature modeling in MRAM devices as they demonstrate a significantly lower switching time than the one in a constant temperature model.

Structural changes in the thalamus and its subregions in regulating different symptoms of posttraumatic stress disorder

As a key center for sensory information processing and transmission, the thalamus plays a crucial role in the development of posttraumatic stress disorder (PTSD). However, the changes in the thalamus and its role in regulating different PTSD symptoms remain unclear. In this study, fourteen PTSD patients and eighteen healthy controls (HCs) were recruited. All subjects underwent whole-brain T1-weighted three-dimensional Magnetization Prepared Rapid Gradient Echo Imaging scans. Gray matter volume (GMV) in the thalamus and its subregions were estimated using voxel-based morphometry (VBM). Compared to HCs, PTSD patients exhibited significant GMV reduction in the left thalamus and its subregions, including anterior, mediodorsal, ventral-lateral-dorsal (VLD), ventral-anterior, and ventral-lateral-ventral (VLV). Among the significantly reduced thalamic subregions, we found positive correlations between the GMV values of the left VLD and VLV and the re-experiencing symptoms score, arousal symptoms score, and total CAPS score. When using the symptom-related GMV values of left VLV and VLD in combination as a predictor, receiver operating characteristic (ROC) analysis revealed that the area under the curve (AUC) for binary classification reached 0.813. This study highlights the neurobiological mechanisms of PTSD related to thalamic changes and may provide potential imaging markers for diagnosis and therapy targets.

A Comprehensive Study of Temperature and Its Effects in SOT-MRAM Devices.

We employ a fully three-dimensional model coupling magnetization, charge, spin, and temperature dynamics to study temperature effects in spin-orbit torque (SOT) magnetoresistive random access memory (MRAM). SOTs are included by considering spin currents generated through the spin Hall effect. We scale the magnetization parameters with the temperature. Numerical experiments show several time scales for temperature dynamics. The relatively slow temperature increase, after a rapid initial temperature rise, introduces an incubation time to the switching. Such a behavior cannot be reproduced with a constant temperature model. Furthermore, the critical SOT switching voltage is significantly reduced by the increased temperature. We demonstrate this phenomenon for switching of field-free SOT-MRAM. In addition, with an external-field-assisted switching, the critical SOT voltage shows a parabolic decrease with respect to the voltage applied across the magnetic tunnel junction (MTJ) of the SOT-MRAM cell, in agreement with recent experimental data.

Electroencephalogram-Based Brain Connectivity Analysis in Prolonged Disorders of Consciousness.

Prolonged disorders of consciousness (pDOC) are common in neurology and place a heavy burden on families and society. This study is aimed at investigating the characteristics of brain connectivity in patients with pDOC based on quantitative EEG (qEEG) and extending a new direction for the evaluation of pDOC. Participants were divided into a control group (CG) and a DOC group by the presence or absence of pDOC. Participants underwent magnetic resonance imaging (MRI) T1 three-dimensional magnetization with a prepared rapid acquisition gradient echo (3D-T1-MPRAGE) sequence, and video EEG data were collected. After calculating the power spectrum by EEG data analysis tool, DTABR ((δ + θ)/(α + β) ratio), Pearson's correlation coefficient (Pearson r), Granger's causality, and phase transfer entropy (PTE), we performed statistical analysis between two groups. Finally, receiver operating characteristic (ROC) curves of connectivity metrics were made. The proportion of power in frontal, central, parietal, and temporal regions in the DOC group was lower than that in the CG. The percentage of delta power in the DOC group was significantly higher than that in the CG, the DTABR in the DOC group was higher than that in the CG, and the value was inverted. The Pearson r of the DOC group was higher than that of CG. The Pearson r of the delta band (Z = -6.71, P < 0.01), theta band (Z = -15.06, P < 0.01), and alpha band (Z = -28.45, P < 0.01) were statistically significant. Granger causality showed that the intensity of directed connections between the two hemispheres in the DOC group at the same threshold was significantly reduced (Z = -82.43, P < 0.01). The PTE of each frequency band in the DOC group was lower than that in the CG. The PTE of the delta band (Z = -42.68, P < 0.01), theta band (Z = -56.79, P < 0.01), the alpha band (Z = -35.11, P < 0.01), and beta band (Z = -63.74, P < 0.01) had statistical significance. Brain connectivity analysis based on EEG has the advantages of being noninvasive, convenient, and bedside. The Pearson r of DTABR, delta, theta, and alpha bands, Granger's causality, and PTE of the delta, theta, alpha, and beta bands can be used as biological markers to distinguish between pDOC and healthy people, especially when behavior evaluation is difficult or ambiguous; it can supplement clinical diagnosis.

Changes in brain gray matter volume in nasopharyngeal carcinoma patients after radiotherapy in long-term follow-up

ObjectivesThe aim of this study was to examine the changes in gray matter in nasopharyngeal carcinoma patients with normal hearing (Group 1) and nasopharyngeal carcinoma patients with hearing loss (Group 2) after radiotherapy using voxel-based morphological analysis and to analyze the relationship with the radiation doses of the temporal lobe. Methods21 patients in Group 1, 14 patients in Group 2, and 21 healthy volunteers were selected. All participants underwent an otologic examination and three-dimensional magnetization preparatory rapid acquisition gradient echo sequence scan. The correlation between the variation of whole brain gray matter volume and the doses of the temporal lobe was analyzed by Data Processing & Analysis for Brain Imaging software. ResultsCompared with the normal control group, the brain areas with reduced gray matter volume in nasopharyngeal carcinoma patients after radiotherapy were mainly in the left posterior cerebellar lobe (T = −8.797), left insular lobe (T = −7.96), and the right insular lobe (T = −6.632). Compared to Group 1, the brain areas of Group 2 patients with reduced gray matter volume were mainly in the left superior temporal gyrus (T = −2.366), left olfactory bulb (T = −2.52), left Rolandic operculum (T = −2.431), and right olfactory bulb (T = −3.100). Compared with Group 1, the brain areas of Group 2 patients with increased gray matter volume were mainly in the left calcarine sulcus (T=3.425) and right calcarine sulcus (T=3.169). There were no correlations between the changes of brain gray matter volume and the radiation doses of the temporal lobe in both Group 1 and Group 2. ConclusionsThe radiotherapy may cause the changes of brain areas associated with cognitive function in nasopharyngeal carcinoma in a long-term follow-up. At the same time, nasopharyngeal carcinoma patients with the radiation-induced hearing loss had abnormal gray matter volumes in the auditory center and other sensory centers. Our findings might provide new understanding into the pathogenesis of radiation-induced brain damage in normal-appearing brain tissue. Yet this exploratory study should be taken with caution.

Poisson-Dirichlet distributions and weakly first-order spin-nematic phase transitions

We provide a quantitative characterization of generic weakly first-order thermal phase transitions out of planar spin-nematic states in three-dimensional spin-one quantum magnets, based on calculations using Poisson-Dirichlet distributions (PD) within a universal loop model formulation, combined with large-scale quantum Monte Carlo calculations. In contrast to earlier claims, the thermal melting of the nematic state is not continuous, instead a weakly first-order transition is identified from both thermal properties and the distribution of the nematic order parameter. Furthermore, based on PD calculations, we obtain exact results for the order parameter distribution and Binder cumulants at the discontinuous melting transition. Our findings establish the thermal melting of planar spin-nematic states as a generic platform for quantitative approaches to weakly first-order phase transitions in quantum systems with a continuous SU(2) internal symmetry.

Clinical study on application of 3D Slicer software assisted domestic frameless stereotactic robot in biopsy of intracranial lesions

Objective: To examine the application value of 3D Slicer software assisted domestic frameless stereotactic robot in biopsy of intracranial lesions. Methods: A retrospective analysis was performed on 80 patients who admitted consecutively and underwent intracerebral lesions biopsy with the domestic frameless stereotactic robot at Department of Neurosurgery, Aerospace Central Hospital from January 2019 to December 2021. There were 36 males and 44 females, with a mean age of (38.5±18.0) years (range: 6 to 71 years). Before surgery only enhanced T1-weighted three-dimensional magnetization prepared gradient echo sequences and diffusion tensor imaging scans were performed. Self-reconstruction of intracranial lesions, cerebral cortex and blood vessels was carried out using 3D Slicer software system after the DICOM format imaging data of 80 patients were collected. These imaging data were merged to the workstation of the domestic frameless stereotactic robot for preoperative surgical planning and the surgical puncture path was designed to avoid blood vessels in the brain functional area, cerebral cortex and sulcus. Results: All frameless stereotactic biopsy were successfully performed. Postoperative pathological diagnosis included 50 cases of diffuse astrocytic and oligodendroglioma, 15 cases of lymphoma, 5 cases of metastatic tumors, 5 cases of inflammatory demyelinating disease, 2 cases of inflammatory granuloma, 1 case of hemangioma, 1 case of acute lymphoblastic leukemia intracranial invasion and 1 case of seminoma. The positive diagnosis rate was 100% (80/80). Postoperative imaging confirmed that the puncture path and target were accurately implemented according to the preoperative planning, and the target error was (1.32±0.44) mm (range: 0.55 to 1.99 mm). One case of puncture-related bleeding occurred at the target after surgery and improved after treatment. Conclusion: The three-dimensional multimodal images reconstructed by the 3D Slicer software before operation could help the surgeons make the preoperative planning and reduce the risk of stereotactic brain biopsy.

Controlling inversion disorder in a stoichiometric spinel magnet

In the study of frustrated quantum magnets, it is essential to be able to control the nature and degree of site disorder during the growth process, as many measurement techniques are incapable of distinguishing between site disorder and frustration-induced spin disorder. Pyrochlore-structured spinel oxides can serve as model systems of geometrically frustrated three-dimensional quantum magnets; however, the nature of the magnetism in one well-studied spinel, ZnFe2O4, remains unclear. Here, we demonstrate simultaneous control of both stoichiometry and inversion disorder in the growth of ZnFe2O4 single crystals, directly yielding a revised understandingof both the collective spin behavior and lattice symmetry. Crystals grown in the stoichiometric limit with minimal site inversion disorder contravene all the previously suggested exotic spin phases in ZnFe2O4. Furthermore, the structure is confirmed on the [Formula: see text] space group with broken inversion symmetry that induces antiferroelectricity. The effective tuning of magnetic behavior by site disorder in the presence of robust antiferroelectricity makes ZnFe2O4 of special interest to multiferroic devices.

Skyrmions and hopfions in three-dimensional frustrated magnets

A model of an inversion-symmetric frustrated spin system is introduced which hosts three-dimensional extensions of magnetic Skyrmions. In the continuum approximation this model reduces to a non-linear sigma model on a squashed sphere which has a natural interpolating parameter. At one limit of the parameter the model reduces to a frustrated magnetic system earlier considered by Sutcliffe as a host to Hopfions, and in the other limit it becomes very similar to the 3D Skyrme model. To better understand the relation between Hopfions and 3D Skyrmions a model interpolating between the Faddeev-Niemi model and the Skyrme model is reconsidered and it is shown that energies of the solitons obey a linear BPS bound. The 3D Skyrmions in the frustrated magnetic model are found and compared to the rational map ansatz.

Magnetic excitations and interactions in the Kitaev hyperhoneycomb iridate β−Li2IrO3

We present a thorough experimental study of the three-dimensional hyperhoneycomb Kitaev magnet $\beta$-Li$_2$IrO$_3$, using a combination of inelastic neutron scattering (INS), time-domain THz spectroscopy, and heat capacity measurements. The main results include a massive low-temperature reorganization of the INS spectral weight that evolves into a broad peak centered around 12 meV, and a distinctive peak in the THz data at 2.8(1) meV. A detailed comparison to powder-averaged spin-wave theory calculations reveals that the positions of these two features are controlled by the anisotropic $\Gamma$ coupling and the Heisenberg exchange $J$, respectively. The refined microscopic spin model places $\beta$-Li$_2$IrO$_3$ in close proximity to the Kitaev spin liquid phase.

Modelling a permanent magnet synchronous motor in FEniCSx for parallel high-performance simulations

There are concerns that the extreme requirements of heavy-duty vehicles and aviation will see them left behind in the electrification of the transport sector, becoming the most significant emitters of greenhouse gases. Engineers extensively use the finite element method to analyse and improve the performance of electric machines, but new highly scalable methods with a linear (or near) time complexity are required to make extreme-scale models viable. This paper introduces a three-dimensional permanent magnet synchronous motor model using FEniCSx, a finite element platform tailored for efficient computing and data handling at scale. The model demonstrates comparable magnetic flux density distributions to a verification model built in Ansys Maxwell with a maximum deviation of 7% in the motor’s static regions. Solving the largest mesh, comprising over eight million cells, displayed a speedup of 198 at 512 processes. A preconditioned Krylov subspace method was used to solve the system, requiring 92% less memory than a direct solution. It is expected that advances built on this approach will allow system-level multiphysics simulations to become feasible within electric machine development. This capability could provide the near real-world accuracy needed to bring electric propulsion systems to large vehicles. • Stable and scalable electric machine analysis is possible using iterative methods. • Open-source solvers can leverage the advantages of high-performance computing. • The parallel performance of FEniCSx exceeds an established electromagnetic code.

Three-dimensional sandglass magnet with non-Kramers ions

Magnetic susceptibility, specific heat, and muon spin relaxation ($\ensuremath{\mu}\mathrm{SR}$) measurements have been performed on a synthesized three-dimensional sandglass-type lattice ${\mathrm{Tm}}_{3}{\mathrm{SbO}}_{7}$, where two inequivalent sets of non-Kramers ${\mathrm{Tm}}^{3+}$ ions (${\mathrm{Tm}}_{1}^{3+}$ and ${\mathrm{Tm}}_{2}^{3+})$ show crystal electrical field effect at different temperature ranges. The existence of an ordered or a glassy state down to 0.1 K in zero field is excluded. The low-energy properties of ${\mathrm{Tm}}_{3}{\mathrm{SbO}}_{7}$ are dominated by the lowest non-Kramers quasidoublet of ${\mathrm{Tm}}_{1}^{3+}$, and the energy splitting is regarded as an intrinsic transverse field. Therefore, the low-temperature paramagnetic phenomenon in ${\mathrm{Tm}}_{3}{\mathrm{SbO}}_{7}$ is explained by a transverse field Ising model, which is supported by the quantitative simulation of specific heat data. In addition, the perturbation from ${\mathrm{Tm}}_{2}^{3+}$ may play an important role in accounting for the low temperature spin dynamics behavior observed by $\ensuremath{\mu}\mathrm{SR}$.

Topological surface currents accessed through reversible hydrogenation of the three-dimensional bulk

Hydrogen, the smallest and most abundant element in nature, can be efficiently incorporated within a solid and drastically modify its electronic and structural state. In most semiconductors interstitial hydrogen binds to defects and is known to be amphoteric, namely it can act either as a donor (H+) or an acceptor (H−) of charge, nearly always counteracting the prevailing conductivity type. Here we demonstrate that hydrogenation resolves an outstanding challenge in chalcogenide classes of three-dimensional (3D) topological insulators and magnets — the control of intrinsic bulk conduction that denies access to quantum surface transport, imposing severe thickness limits on the bulk. With electrons donated by a reversible binding of H+ ions to Te(Se) chalcogens, carrier densities are reduced by over 1020cm−3, allowing tuning the Fermi level into the bulk bandgap to enter surface/edge current channels without altering carrier mobility or the bandstructure. The hydrogen-tuned topological nanostructures are stable at room temperature and tunable disregarding bulk size, opening a breadth of device platforms for harnessing emergent topological states.

Dynamical signatures of rank-2 U(1) spin liquids

Emergent $U(1)$ gauge theories and artificial photons in frustrated magnets are outstanding examples of many-body collective phenomena. The classical and quantum regimes of these systems provide platforms for classical and quantum spin liquids, and are the subject of current active theoretical and experimental investigations. Recently, realizations of rank-2 $U(1)$ (R2-U1) gauge theories in three-dimensional frustrated magnets have been proposed. Such systems in the quantum regime may lead to the so-called fracton ordered phases---a new class of topological order that has been associated with quantum stabilizer codes and holography. However, there exist few distinguishing characteristics of these states for their detection in real materials. Here we focus on the classical limit and present the dynamical spin structure factor for a R2-U1 spin liquid state on a breathing pyrochlore lattice. Remarkably, we find unique signatures of the R2-U1 state, and we contrast them with the results obtained from a more conventional $U(1)$ spin liquid. These results provide a path of investigation for future inelastic neutron scattering experiments on candidate materials.