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Recently, Yb-based triangular-lattice antiferromagnets have garnered significant interest as possible quantum spin-liquid candidates. One example is YbMgGaO4, which showed many promising spin-liquid features, but also possesses a high degree of disorder owing to site-mixing between the non-magnetic cations. To further elucidate the role of chemical disorder and to explore the phase diagram of these materials in applied field, we present neutron scattering and sensitive magnetometry measurements of the closely related compound, YbZnGaO4. Our results suggest a difference in magnetic anisotropy between the two compounds, and we use key observations of the magnetic phase crossover to motivate an exploration of the field- and exchange parameter-dependent phase diagram, providing an expanded view of the available magnetic states in applied field. This enriched map of the phase space serves as a basis to restrict the values of parameters describing the magnetic Hamiltonian with broad application to recently discovered related materials.

We report a comprehensive study of the spin ladder compound BaFe2S2.5Se0.5 using neutron diffraction, inelastic neutron scattering, high pressure synchrotron diffraction, and high pressure transport techniques. We find that BaFe2S2.5Se0.5 possesses the same Cmcm structure and stripe antiferromagnetic order as does BaFe2S3, but with a reduced Néel temperature of TN=98 K compared to 120 K for the undoped system, and a slightly increased ordered moment of 1.40μB per iron. The low-energy spin excitations in BaFe2S2.5Se0.5 are likewise similar to those observed in BaFe2S3. However, unlike the reports of superconductivity in BaFe2S3 below Tc∼14 K under pressures of 10 GPa or more, we observe no superconductivity in BaFe2S2.5Se0.5 at any pressure up to 19.7 GPa. In contrast, the resistivity exhibits an upturn at low temperature under pressure. Furthermore, we show that additional high-quality samples of BaFe2S3 synthesized for this study likewise fail to become superconducting under pressure, instead displaying a similar upturn in resistivity at low temperature. These results demonstrate that microscopic, sample-specific details play an important role in determining the ultimate electronic ground state in this spin ladder system. We suggest that the upturn in resistivity at low temperature in both BaFe2S3 and BaFe2S2.5Se0.5 may result from Anderson localization induced by S vacancies and random Se substitutions, enhanced by the quasi-one-dimensional ladder structure.

Novel electronic phenomena frequently form in heavy-fermions because of the mutual localized and itinerant nature of f-electrons. On the magnetically ordered side of the heavy-fermion phase diagram, f-moments are expected to be localized and decoupled from the Fermi surface. It remains ambiguous whether Kondo lattice can develop inside the magnetically ordered phase. Using spectroscopic imaging with scanning tunneling microscope, complemented by neutron scattering, x-ray absorption spectroscopy, and dynamical mean field theory, we probe the electronic states in antiferromagnetic USb2. We visualize a large gap in the antiferromagnetic phase within which Kondo hybridization develops below ~80 K. Our calculations indicate the antiferromagnetism and Kondo lattice to reside predominantly on different f-orbitals, promoting orbital selectivity as a new conception into how these phenomena coexist in heavy-fermions. Finally, at 45 K, we find a novel first order-like transition through abrupt emergence of nontrivial 5f-electronic states that may resemble the "hidden-order" phase of URu2Si2.

Uranium compounds can manifest a wide range of fascinating many-body phenomena, and are often thought to be poised at a crossover between localized and itinerant regimes for 5f electrons. The antiferromagnetic dipnictide USb2 has been of recent interest due to the discovery of rich proximate phase diagrams and unusual quantum coherence phenomena. Here, linear-dichroic X-ray absorption and elastic neutron scattering are used to characterize electronic symmetries on uranium in USb2 and isostructural UBi2. Of these two materials, only USb2 is found to enable strong Hund's rule alignment of local magnetic degrees of freedom, and to undergo distinctive changes in local atomic multiplet symmetry across the magnetic phase transition. Theoretical analysis reveals that these and other anomalous properties of the material may be understood by attributing it as the first known high temperature realization of a singlet ground state magnet, in which magnetism occurs through a process that resembles exciton condensation.

The pressure evolution of the magnetic properties of the Ce2RhIn7.79Cd0.21 heavy fermion compound was investigated by single crystal neutron magnetic diffraction and electrical resistivity experiments under applied pressure. From the neutron magnetic diffraction data, up to P = 0.6 GPa, we found no changes in the magnetic structure or in the ordering temperature TN = 4.8 K. However, the increase of pressure induces an interesting spin rotation of the ordered antiferromagnetic moment of Ce2RhIn7.79Cd0.21 into the ab tetragonal plane. From the electrical resistivity measurements under pressure, we have mapped the evolution of TN and the maximum of the temperature dependent electrical resistivity (TMAX) as a function of the pressure (P ≲ 3.6 GPa). To gain some insight into the microscopic origin of the observed spin rotation as a function of pressure, we have also analyzed some macroscopic magnetic susceptibility data at ambient pressure for pure and Cd-doped Ce2RhIn8 using a mean-field model including tetragonal crystalline electric field (CEF). The analysis indicates that these compounds have a Kramers doublet Γ7- -type ground state, followed by a Γ7+ first excited state at Δ1 ∼ 80 K and a Γ6 second excited state at Δ2 ∼ 270 K for Ce2RhIn8 and Δ2 ∼ 250 K for Ce2RhIn7.79Cd0.21. The evolution of the magnetic properties of Ce2RhIn8 as a function of Cd doping and the rotation of the direction of the ordered moment for the Ce2RhIn7.79Cd0.21 compound under pressure suggest important changes of the single ion anisotropy of Ce3+ induced by applying pressure and Cd doping in these systems. These changes are reflected in modifications in the CEF scheme that will ultimately affect the actual ground state of these compounds.

An essential step toward elucidating the mechanism of superconductivity is to determine the sign or phase of the superconducting order parameter, as it is closely related to the pairing interaction. In conventional superconductors, the electron-phonon interaction induces attraction between electrons near the Fermi energy and results in a sign-preserved s-wave pairing. For high-temperature superconductors, including cuprates and iron-based superconductors, prevalent weak coupling theories suggest that the electron pairing is mediated by spin fluctuations which lead to repulsive interactions, and therefore that a sign-reversed pairing with an s_{±} or d-wave symmetry is favored. Here, by using magnetic neutron scattering, a phase sensitive probe of the superconducting gap, we report the observation of a transition from the sign-reversed to sign-preserved Cooper-pairing symmetry with insignificant changes in T_{c} in the S-doped iron selenide superconductors K_{x}Fe_{2-y}(Se_{1-z}S_{z})_{2}. We show that a rather sharp magnetic resonant mode well below the superconducting gap (2Δ) in the undoped sample (z=0) is replaced by a broad hump structure above 2Δ under 50% S doping. These results cannot be readily explained by simple spin fluctuation-exchange pairing theories and, therefore, multiple pairing channels are required to describe superconductivity in this system. Our findings may also yield a simple explanation for the sometimes contradictory data on the sign of the superconducting order parameter in iron-based materials.

An inelastic neutron scattering study of the spin waves corresponding to the stripe antiferromagnetic order in insulating Rb0.8Fe1.5S2 throughout the Brillouin zone is reported. The spin wave spectra are well described by a Heisenberg Hamiltonian with anisotropic in-plane exchange interactions. Integrating the ordered moment and the spin fluctuations results in a total moment squared of 27.6±4.2μB2/Fe, consistent with S≈2. Unlike XFe2As2 (X=Ca, Sr, and Ba), where the itinerant electrons have a significant contribution, our data suggest that this stripe antiferromagnetically ordered phase in Rb0.8Fe1.5S2 is a Mott-like insulator with fully localized 3d electrons and a high-spin ground state configuration. Nevertheless, the anisotropic exchange couplings appear to be universal in the stripe phase of Fe pnictides and chalcogenides.

Electric resistivity, specific heat, magnetic susceptibility, and inelastic neutron scattering experiments were performed on a single crystal of the heavy fermion compound Ce(Ni0.935Pd0.065)2Ge2 in order to study the spin fluctuations near an antiferromagnetic (AF) quantum critical point (QCP). The resistivity and the specific heat coefficient for T ⩽ 1 K exhibit the power law behavior expected for a 3D itinerant AF QCP (ρ(T) ∼ T(3/2) and γ(T) ∼ γ0 - bT(1/2)). However, for 2 ⩽ T ⩽ 10 K, the susceptibility and specific heat vary as log T and the resistivity varies linearly with temperature. Furthermore, despite the fact that the resistivity and specific heat exhibit the non-Fermi liquid behavior expected at a QCP, the correlation length, correlation time, and staggered susceptibility of the spin fluctuations remain finite at low temperature. We suggest that these deviations from the divergent behavior expected for a QCP may result from alloy disorder.

Low-temperature magnetic properties of Cd-doped Ce2 M In 8 (M=Rh and Ir) single crystals are investigated. Experiments of temperature-dependent magnetic-susceptibility, heat-capacity, and electrical-resistivity measurements revealed that Cd doping enhances the antiferromagnetic (AFM) ordering temperature from TN =2.8 K (x=0) to TN =4.8 K (x=0.21) for Ce2 RhIn8-x Cd x and induces long-range AFM ordering with TN =3.8 K (x=0.21) for Ce2 IrIn8-x Cdx. Additionally, x-ray and neutron magnetic scattering studies showed that Cd-doped samples present below TN a commensurate antiferromagnetic structure with a propagation vector ε→ = (1/2, 1/2, 0). The resolved magnetic structures for both compounds indicate that the Cd doping tends to rotate the direction of the ordered magnetic moments toward the ab plane. This result suggests that the Cd doping affects the Ce3+ ground-state single-ion anisotropy modifying the crystalline electrical field (CEF) parameters at the Ce3+ site. Indications of CEF evolution induced by Cd doping were also found in the electrical-resistivity measurements. Comparisons between our results and the general effects of Cd doping on the related compounds CeMIn 5 (M=Co, Rh, and Ir) confirms the claims that the Cd doping induced electronic tuning is the main effect favoring AFM ordering in these compounds. © 2010 The American Physical Society.

Low-temperature magnetic properties of Cd-doped Ce2 M In 8 (M=Rh and Ir) single crystals are investigated. Experiments of temperature-dependent magnetic-susceptibility, heat-capacity, and electrical-resistivity measurements revealed that Cd doping enhances the antiferromagnetic (AFM) ordering temperature from TN =2.8 K (x=0) to TN =4.8 K (x=0.21) for Ce2 RhIn8-x Cd x and induces long-range AFM ordering with TN =3.8 K (x=0.21) for Ce2 IrIn8-x Cdx. Additionally, x-ray and neutron magnetic scattering studies showed that Cd-doped samples present below TN a commensurate antiferromagnetic structure with a propagation vector ε→ = (1/2, 1/2, 0). The resolved magnetic structures for both compounds indicate that the Cd doping tends to rotate the direction of the ordered magnetic moments toward the ab plane. This result suggests that the Cd doping affects the Ce3+ ground-state single-ion anisotropy modifying the crystalline electrical field (CEF) parameters at the Ce3+ site. Indications of CEF evolution induced by Cd doping were also found in the electrical-resistivity measurements. Comparisons between our results and the general effects of Cd doping on the related compounds CeMIn 5 (M=Co, Rh, and Ir) confirms the claims that the Cd doping induced electronic tuning is the main effect favoring AFM ordering in these compounds. © 2010 The American Physical Society.

We show using neutron diffraction that the magnetic structure of CeRhIn4.85 Hg0.15 is characterized by a commensurate propagation vector (1/2,1/2,1/2). This is different from the magnetic structure in the parent compound CeRhIn5, which orders with an incommensurate propagation vector (1/2,1/2,0.297). The special relation between the commensurate magnetic mode and unconventional superconductivity has been shown previously for this class of heavy fermion superconductors. This work provides further evidence for the ubiquity of this antiferromagnetic mode. © 2009 The American Physical Society.

Neutron scattering data from the cubic heavy-fermion compound YbBiPt are presented, along with an interpretation in terms of strongly broadened crystal-field levels. To first order, the ground state is sixfold degenerate, consisting of a doublet (7) and quartet (8). Integration over these levels reproduces the observed linear specific-heat coefficient of 8 J mol -1 K -2 to within 20%. At the lowest temperatures, an extra symmetry-forbidden splitting is observed. © 1995 The American Physical Society.

Polarized and unpolarized neutron scattering techniques along with x-ray diffraction have been used to study the magnetic and structural properties of a single crystal of Nd2CuO4. Long-range magnetic order of the Cu moments develops at TN=245 K, with a simple antiferromagnetic configuration of spins as found in La2NiO4, while the spin directions may be either collinear or noncollinear. Additional abrupt transitions are observed at 75 and 30 K, in which spin reorientations take place. Bragg peaks associated with the crystal structure are found at the same positions as the magnetic Bragg peaks, and indicate that a small distortion of the basic tetragonal structure has occurred above 300 K. At low temperatures the Nd moments also order antiferromagnetically (TN=1.5 K), while an additional transition of a continuous nature is observed at 150 mK.

Polarized and unpolarized neutron-diffraction measurements have been taken to determine the magnetic structure of the Cu spins in the RBa2Cu3O6+x system as a function of temperature. Most of the results have been obtained on two (semiconducting) oxygen-deficient single crystals of composition NdBa2Cu3O6.1 and NdBa2Cu3O6.35. On cooling from the paramagnetic state, the Cu-O plane layers first order at a Néel temperature TN1 in a simple antiferromagnetic arrangement of spins, with TN1=430 K for x=0.1 and TN1=230 K for x=0.35, and with a saturated moment of 0.65B. At a lower temperature TN2 the Cu chain layer also orders, with TN2=80 and 10 K for x=0.1 and 0.35, respectively. Hence both transition temperatures decrease with increasing oxygen concentration in this range of x, and the qualitative behavior for these two samples is found to be identical. We have not, however, observed this low-T structure in polycrystalline samples of either YBa2Cu3O6+x or NdBa2Cu3O6+x, and some possible explanations for this difference in behavior are discussed. For the single crystals in the low-T phase the Cu spins in all three copper-oxygen layers are ordered in a simple antiferromagnetic arrangement, with the magnetic unit cell double the chemical unit cell along all three crystallographic directions. On the basis of the measured integrated intensities of over 40 magnetic reflections in both ordered phases, the results can be accounted for quantitatively with the assumption of a 3d magnetic form factor on the Cu ions, with no need for a significant moment on any of the oxygen ions. At low T, site-averaged moments of 0.35B and 0.8B are obtained in the chain and the plane layers, respectively. The fact that the ordered moment on the plane layers increases in the low-T phase is direct evidence that two-dimensional quantum fluctuations play an important role in the plane layers in the high-T ordered phase. The evolution of the low-T spin structure into the high-T structure involves a noncollinear configuration in which the spins rotate as a function of temperature in the plane layers, while the chain layer becomes thermally disordered. The temperature dependence of the structure indicates that competing interactions between the layers are important, and this is discussed in detail. Finally, exploratory measurements as a function of applied magnetic field indicate that the magnetic anisotropy in the tetragonal plane is much smaller than the exchange energies. © 1990 The American Physical Society.

Neutron-diffraction techniques have been used to study the magnetic ordering of the Nd ions in semiconducting Nd2CuO4 and superconducting Nd1.85Ce0.15CuO4. For the Ce-doped system a sharp transition to long-range antiferromagnetic order occurs at TN1.2 K, with a simple magnetic unit cell which is double the chemical unit cell along the a and b directions. The same magnetic structure is observed in the parent system Nd2CuO4, in which the Cu spins are also ordered magnetically, but strong coupling between the Nd and Cu sublattices is indicated. © 1990 The American Physical Society.

Neutron-diffraction measurements have been carried out as a function of hydrostatic pressure to study the magnetic order of the Cu spins in NdBa2Cu3O6.35 and NdBa2Cu3O6.1. In the high-temperature phase, where the Cu planes order antiferromagnetically, we find that the Néel temperature TN1 is very strongly dependent on pressure, increasing at the rate of 1/423 K/kbar. We attribute this phenomenal sensitivity to the two-dimensional-like behavior of this magnetic system. In the low-temperature phase, which is associated with magnetic ordering of the chains, only a small change in the ordering temperature TN2 is observed. © 1989 The American Physical Society.

Neutron-diffraction measurements have been taken on single crystals of NdBa2Cu3O6+x to explore the nature of the magnetic order as a function of oxygen concentration x. The Cu-O planes are known to order antiferromagnetically at TN1, with TN1(x0) 450 K. At lower temperatures we find that the oxygen-deficient Cu planes also order magnetically [TN2(x0.1) 80 K], with a large ordered moment of 0.46B and a simple antiferromagnetic sequencing along the c axis. Both ordering temperatures decrease with increasing x, with TN2 being much more sensitive to x than TN1. © 1988 The American Physical Society.

We have employed polarized and unpolarized neutron-diffraction techniques on both powders and single crystals to establish the nature of the magnetic order of the Cu ions in oxygen-deficient (nonsuperconducting) RBa2Cu3O6+x (R=Y,Nd). Magnetic Bragg peaks of the type (h2,k2,l) are observed that yield a magnetic structure in which the Cu spins are coupled antiferromagnetically both in the Cu-O planes as well as along the tetragonal c axis, with the spin direction in the tetragonal plane. The Néel temperature is very sensitive to the oxygen content, with TN(x1/40)500 K, while the spin configuration is independent of x. © 1988 The American Physical Society.

Neutron and X-ray diffraction have been used to study the magnetic and structural properties of single crystal Nd2CuO4. Long range magnetic order of the Cu moments develops at TN=245 K, with a noncollinear antiferromagnetic arrangement of spins. Additional abrupt transitions are observed at 75 K and 30 K, in which a spin reorientation takes place. Bragg peaks associated with the crystal structure are found at the same positions as the magnetic Bragg peaks, and indicate that a distortion of the basic tetragonal structure has occurred above 300 K. © 1989.

Ferroic materials on the verge of forming ferroic glasses exhibit heightened functionality that is often attributed to competing long- and short-range correlations. However, the physics underlying these enhancements is not well understood. The Ni 45 Co 5 Mn 36.6 In 13.4 Heusler alloy is on the edge of forming both spin and strain glasses and exhibits magnetic field-induced shape memory and large magnetocaloric effects, making it a candidate for multicaloric cooling applications. We show using neutron scattering that localized magnon-phonon hybrid modes, which are inherently spread across reciprocal space, act as a bridge between phonons and magnons and result in substantial magnetic field-induced shifts in the phonons, triple the caloric response, and alter phase stability. We attribute these modes to the localization of phonons and magnons by antiphase boundaries coupled to magnetic domains. Because the interplay between short- and long-range correlations is common near ferroic glassy states, our work provides general insights on how glassiness enhances function.

Ferromagnetic (FM) order in a two-dimensional kagome layer is predicted to generate a topological Chern insulator without an applied magnetic field. The Chern gap is largest when spin moments point perpendicular to the kagome layer, enabling the capability to switch topological transport properties, such as the quantum anomalous Hall effect, by controlling the spin orientation. In TbMn 6 Sn 6 , the uniaxial magnetic anisotropy of the Tb 3+ ion is effective at generating the Chern state within the FM Mn kagome layers while a spin-reorientation (SR) transition to easy-plane order above T SR  = 310 K provides a mechanism for switching. Here, we use inelastic neutron scattering to provide key insights into the fundamental nature of the SR transition. The observation of two Tb excitations, which are split by the magnetic anisotropy energy, indicates an effective two-state orbital character for the Tb ion, with a uniaxial ground state and an isotropic excited state. The simultaneous observation of both modes below T SR confirms that orbital fluctuations are slow on magnetic and electronic time scales < ps and act as a spatially-random orbital alloy. A thermally-driven critical concentration of isotropic Tb ions triggers the SR transition., (© 2023. The Author(s).)

We report the magnetic ordering and structural distortion in PrFeAsO crystals, the basis compound for one of the oxypnictide superconductors, using high-resolution x-ray diffraction, neutron diffraction, and x-ray resonant magnetic scattering (XRMS). We find the structural tetragonal-to-orthorhombic phase transition at T S = 147 K , the AFM phase transition of the Fe moments at T Fe = 72 K , and the Pr AFM phase transition at T Pr = 21 K . Combined high-resolution neutron diffraction and XRMS show unambiguously that the Pr moments point parallel to the longer orthorhombic a axis and order antiferromagnetically along the a axis but ferromagnetically along the b and c directions in the stripelike AFM order. The temperature-dependent magnetic order parameter of the Pr moments shows no evidence for a reorientation of moments.

Magnetic structure of the Co ions in monoclinic Co 3 TeO 6 in the antiferroelectric state at 16 K has been determined by neutron powder together with single-crystal diffractions. The indices of the magnetic reflections that appear at the incommensurate positions were determined by diffractions from a single crystal, which allow to uniquely identify the magnetic modulation vector. There are two crystallographically distinct Co layers. Magnetic incommensurability appears in the Co spins in the layers comprising zig-zag chains, with a magnetic modulation vector of (0.357, 0.103, 0.121) at 3 K but changes to (0.4439, 0, 0.137) at 16 K, while the Co ions in the honeycomb webs form a collinear antiferromagnetic structure. Thermal reduction rate of the Co moments in the honeycomb webs was found to be much smaller than those in the zigzag chains. Shifting of large amounts of electronic charge into the Co─O bonds in the honeycomb webs on warming is used to understand the behavior.

The coupling between the organic CH 3 NH 3 + cations and inorganic perovskite PbBr 3 - framework in a large single crystal of (CH 3 NH 3 )PbBr 3 weighting 13 g was studied using neutron diffraction and inelastic neutron scattering. Two lattice incommensurate (ICM) phases were found, one at higher temperatures, marked ICM HT , which appeared between 147 and 135 K. The second one, marked ICM LT , developed below 143 K and remained at 75 K. The transition from the ICM LT to ICM HT phase upon warming gave rise to extremely large lattice shrinking, followed by extremely large lattice expansion of the tetragonal basal plane of the PbBr 3 lattice. There was a progressive decrease in the width of the Bragg peaks from the PbBr 3 lattice upon warming, which can be described using a critical exponent for each type of Bragg peak to show complete ordering of the atoms into a (CH 3 NH 3 )PbBr 3 lattice at 194 K. (CH 3 NH 3 )PbBr 3 exhibits six definitive acoustic-like phonon branches at 75 K. The six branches renormalizes into two at 200 K, with the frequencies of both the transverse and longitudinal modes greatly enhanced. The asymmetric structure of the CH 3 NH 3 ions helps to understand the observed behaviors.

Anisotropy and competing exchange interactions have emerged as two central ingredients needed for centrosymmetric materials to exhibit topological spin textures. Fe 3 Sn 2 is thought to have these ingredients as well, as it has recently been discovered to host room temperature skyrmionic bubbles with an accompanying topological Hall effect. We present small-angle inelastic neutron scattering measurements that unambiguously show that Fe 3 Sn 2 is an isotropic ferromagnet below T C ≈ 660     K to at least 480 K - the lower temperature threshold of our experimental configuration. Fe 3 Sn 2 is known to have competing magnetic exchange interactions, correlated electron behavior, weak magnetocrystalline anisotropy, and lattice anisotropy; all of these features are thought to play a role in stabilizing skyrmions in centrosymmetric systems. Our results reveal that at elevated temperatures, there is an absence of magnetocrystalline anisotropy and that the system behaves as a typical exchange ferromagnet with a spin stiffness D T = 0   K = 271 ± 9   meV     Å 2 ., Competing Interests: Conflicts of Interest: The identification of any commercial product or trade name does not imply endorsement or recommendation by the National Institute of Standards and Technology. The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

Identification, understanding, and manipulation of novel magnetic textures are essential for the discovery of new quantum materials for future spin-based electronic devices. In particular, materials that manifest a large response to external stimuli such as a magnetic field are subject to intense investigation. Here, we study the kagome-net magnet YMn 6 Sn 6 by magnetometry, transport, and neutron diffraction measurements combined with first-principles calculations. We identify a number of nontrivial magnetic phases, explain their microscopic nature, and demonstrate that one of them hosts a large topological Hall effect (THE). We propose a previously unidentified fluctuation-driven mechanism, which leads to the THE at elevated temperatures. This interesting physics comes from parametrically frustrated interplanar exchange interactions that trigger strong magnetic fluctuations. Our results pave a path to chiral spin textures, promising for novel spintronics., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

A small in-plane external uniaxial pressure has been widely used as an effective method to acquire single domain iron pnictide BaFe 2 As 2 , which exhibits twin-domains without uniaxial strain below the tetragonal-to-orthorhombic structural (nematic) transition temperature T s . Although it is generally assumed that such a pressure will not affect the intrinsic electronic/magnetic properties of the system, it is known to enhance the antiferromagnetic (AF) ordering temperature T N ( < T s ) and create in-plane resistivity anisotropy above T s . Here we use neutron polarization analysis to show that such a strain on BaFe 2 As 2 also induces a static or quasi-static out-of-plane (c-axis) AF order and its associated critical spin fluctuations near T N /T s . Therefore, uniaxial pressure necessary to detwin single crystals of BaFe 2 As 2 actually rotates the easy axis of the collinear AF order near T N /T s , and such effects due to spin-orbit coupling must be taken into account to unveil the intrinsic electronic/magnetic properties of the system.

We report the evolution of the magnetic properties of C e 2 R h 1 - x I r x I n 8 - y C d y single crystals. In particular, for C e 2 R h 0.5 I r 0.5 I n 8 ( T N = 2.0 K ) and C e 2 R h 0.5 I r 0.5 I n 7.79 C d 0.21 ( T N = 4.2 K ), we have solved the magnetic structure of these compounds using single-crystal neutron magnetic diffraction experiments. Taking the magnetic structure of the C e 2 R h I n 8 heavy-fermion antiferromagnet as a reference, we have identified no changes in the q = 1 2 , 1 2 , 0 magnetic wave vector; however, the direction of the ordered Ce 3+ moments rotates toward the a b plane, under the influence of both dopants. By constraining the analysis of the crystalline electric field (CEF) with the experimental ordered moment's direction and high-temperature magnetic-susceptibility data, we have used a mean-field model with tetragonal CEF and exchange interactions to gain insight into the CEF scheme and anisotropy of the CEF ground-state wave function when Cd and Ir are introduced into C e 2 R h I n 8 . Consistent with previous work, we find that Cd doping in C e 2 R h I n 8 tends to rotate the magnetic moment toward the a b plane and lower the energy of the CEF excited states' levels. Interestingly, the presence of Ir also rotates the magnetic moment towards the a b plane although its connection to the CEF overall splitting evolution for the y = 0 samples may not be straightforward. These findings may shed light on the origin of the disordered spin-glass phase on the Ir-rich side of the phase diagram and also indicate that the C e 2 M I n 8 compounds may not follow exactly the same Rh-Ir CEF effects trend established for the C e 2 M I n 5 compounds.

We have performed X-ray powder diffraction, magnetization, electrical resistivity, heat capacity and inelastic neutron scattering (INS) to investigate the physical properties of the intermetallic series of compounds CeCuBi 2 - x Sb x . These compounds crystallize in a tetragonal structure with space group P 4 ∕ n m m and present antiferromagnetic transition temperatures ranging from 3.6 K to 16 K. Remarkably, the magnetization easy axis changed along the series, which is closely related to the variations of the tetragonal crystalline electric field (CEF) parameters. This evolution was analyzed using a mean field model, which included an anisotropic nearest-neighbor interactions and the tetragonal CEF Hamiltonian. We obtained the CEF parameters by fitting the magnetic susceptibility data with the constraints given by the INS measurements. More broadly, we discuss how this CEF evolution can affect the Kondo physics and the search for a superconducting state in this family.

The recent reports of superconductivity in Nd 1- x Sr x NiO 2 /SrTiO 3 heterostructures have reinvigorated interest in potential superconductivity of low-oxidation state nickelates. Synthesis of Ni 1+ -containing compounds is notoriously difficult. In the current work, a combined sol-gel combustion and high-pressure annealing technique was employed to prepare polycrystalline perovskite Nd 1- x Sr x NiO 3 ( x = 0, 0.1, and 0.2). Metal nitrates and metal acetates were used as starting materials, and the latter were found to be superior to the former in terms of safety and reactivity. The Nd 1- x Sr x NiO 3 compounds were subsequently reduced to Nd 1- x Sr x NiO 2 using calcium hydride in a sealed, evacuated quartz tube. To understand the synthesis pathway, the evolution from NdNiO 3 to NdNiO 2 was monitored using in situ synchrotron x-ray diffraction during the reduction process. Electrical transport properties were consistent with an insulator-metal transition occurring between x = 0 and 0.1 for Nd 1- x Sr x NiO 3 . Superconductivity was not observed in our bulk samples of Nd 1- x Sr x NiO 2 . Neutron diffraction experiments at 3 and 300 K were performed on Nd 0.9 Sr 0.1 NiO 2 , in which no magnetic Bragg reflections were observed, and the results of structural Rietveld refinement are provided.

The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition, and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most phenomena have focused on electronic properties rather than on phonon properties. One prominent exception is the Kohn anomaly, where phonon softening can emerge when the phonon wave vector nests the Fermi surface of metals. Here we report a new class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by field-theoretical calculations, and experimentally observed through inelastic x-ray and neutron scattering on WSM tantalum phosphide. Compared to the conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple topological singularities of Weyl nodes, leading to a distinct nesting condition with chiral selection, a power-law divergence, and non-negligible dynamical effects. Our work brings the concept of the Kohn anomaly into WSMs and sheds light on elucidating the EPI mechanism in emergent topological materials.

We report the electronic and magnetic properties of stoichiometric CeAuBi 2 single crystals. At ambient pressure, CeAuBi 2 orders antiferromagnetically below a Néel temperature ( T N ) of 19 K. Neutron diffraction experiments revealed an antiferromagnetic propagation vector τ ^ = [ 0 , 0 , 1 ∕ 2 ] , which doubles the paramagnetic unit cell along the c axis. At low temperatures several metamagnetic transitions are induced by the application of fields parallel to the c axis, suggesting that the magnetic structure of CeAuBi 2 changes as a function of field. At low temperatures, a linear positive magnetoresistance may indicate the presence of band crossings near the Fermi level. Finally, the application of external pressure favors the antiferromagnetic state, indicating that the 4 f electrons become more localized.

We report experimental studies of a series of BaFe 2 S 3- x Se x (0 ⩽ x ⩽ 3) single crystals and powder specimens using x-ray diffraction, neutron-diffraction, muon-spin-relaxation, and electrical transport measurements. A structural transformation from Cmcm (BaFe 2 S 3 ) to Pnma (BaFe 2 Se 3 ) was identified around x = 0.7 - 1. Neutron-diffraction measurements on the samples with x = 0.2, 0.4, and 0.7 reveal that the Néel temperature of the stripe antiferromagnetic order is gradually suppressed from ~120 to 85 K, while the magnitude of the ordered Fe 2+ moments shows very little variation. Similarly, the block antiferromagnetic order in BaFe 2 Se 3 remains robust for 1.5 ⩽ x ⩽ 3 with negligible variation in the ordered moment and a slight decrease of the Néel temperature from 250 K ( x = 3) to 225 K ( x = 1.5). The sample with x = 1 near the Cmcm and Pnma border shows coexisting, two-dimensional, short-range stripe- and block-type antiferromagnetic correlations. The system remains insulating for all x , but the thermal activation gap shows an abrupt increase when traversing the boundary from the Cmcm stripe phase to the Pnma block phase. The results demonstrate that the crystal structure, magnetic order, and electronic properties are strongly coupled in the BaFe 2 S 3- x Se x system.

Time-of-flight neutron data reveal spin waves in the ferromagnetic ground state of the kagome staircase material Co 3 V 2 O 8 . While previous work has treated this material as quasi-two-dimensional, we find that an inherently three-dimensional description is needed to describe the spin wave spectrum throughout reciprocal space. Moreover, spin wave branches show gaps that point to an unexpectedly large Dzyaloshinskii-Moriya interaction on the nearest-neighbor bond, with D 1 ≥ J 1 /2. A better understanding of the Dzyaloshinskii-Moriya interaction in this material should shed light on the multiferroicity of the related Ni 3 V 2 O 8 . At a higher temperature where Co 3 V 2 O 8 displays an antiferromagnetic spin density wave structure, there are no well-defined spin wave excitations, with most of the spectral weight observed in broad diffuse scattering centered at the (0, 0.5, 0) antiferromagnetic Bragg peak., (Copyright © 2020 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

We report on the evolution of the average and depth-dependent magnetic order in thin-film samples of biaxially stressed and electron-doped EuTiO 3 for samples across a doping range < 0.1 to 7.8 × 10 20 cm -3 . Under an applied in-plane magnetic field, the G -type antiferromagnetic ground state undergoes a continuous spin-flop phase transition into in-plane, field-polarized ferromagnetism. The critical field for ferromagnetism slightly decreases with an increasing number of free carriers, yet the field evolution of the spin-flop transition is qualitatively similar across the doping range. Unexpectedly, we observe interfacial ferromagnetism with saturated Eu 2+ moments at the substrate interface at low fields preceding ferromagnetic saturation throughout the bulk of the degenerate semiconductor film. We discuss the implications of these findings for the unusual magnetotransport properties of this compound.

Typically, quantum spin liquid candidates can be found in materials with a combination of geometrical frustration along with low spin. Due to its spin of S  =  1/2 the copper (II) ion is often present in the discussion on spin liquid candidates. The solid state compound Ca 3 Cu 2 GeV 2 O 12 is a material that crystallizes in the garnet structure (s.g. #230, Ia-3d), where 3D frustration is known to occur. Heat capacity has shown a lack of magnetic ordering down to 0.35 K, confirmed with low temperature neutron diffraction to 0.07 K. This system displays a Weiss temperature of  -0.93(1) K indicating net antiferromagnetic interactions and significant J 1 -J 2 competition causing frustration. Using both neutron and x-ray diffraction along with heat capacity and magnetometry, the work presented here shows Ca 3 Cu 2 GeV 2 O 12 has potential as a new spin liquid candidate.

The (Li 1- x Fe x OH)FeSe superconductor has been suspected of exhibiting long-range magnetic ordering due to Fe substitution in the LiOH layer. However, no direct observation such as magnetic reflection from neutron diffraction has been reported. Here, we use a chemical design strategy to manipulate the doping level of transition metals in the LiOH layer to tune the magnetic properties of the (Li 1- x-y Fe x Mn y OD)FeSe system. We find Mn doping exclusively replaces Li in the hydroxide layer resulting in enhanced magnetization in the (Li 0.876 Fe 0.062 Mn 0.062 OD)FeSe superconductor without significantly altering the superconducting behavior as resolved by magnetic susceptibility and electrical/thermal transport measurements. As a result, long-range magnetic ordering was observed below 12 K with neutron diffraction measurements. This work has implications for the design of magnetic superconductors for the fundamental understanding of superconductivity and magnetism in the iron chalcogenide system as well as exploitation as functional materials for next-generation devices.

In this study, the inelastic neutron scattering probe of SIKA in ANSTO is employed to investigate the magnon dispersion curve in ferromagnetic SrRuO 3 single crystal epitaxial films and to better understand the underlying mechanisms. This report presents the successful measurement of a magnon peak from the SrRuO 3 films which contained an amount of material of only 0.9 mg. We reveal one significant magnon dispersion curve along [002] following the quadratic E ∝ Q 2 ) relation, which shows a magnon gap of 0.32 meV. We have discussed several possible mechanisms, such as the higher symmetry structure and the impurity levels, which may contribute to this smaller gap.