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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Magnetic field induced phase transition in spinel GeNi 2 O 4

Cubic spinel GeNi 2 O 4 exhibits intriguing magnetic properties with two successive antiferromagnetic phase transitions (T N1 ≈ 12.1 and T N2 ≈ 11.4 K) with the absence of any structural transition. We have performed detailed heat capacity and magnetic measurements in different crystallographic orientations. A new magnetic phase in presence of magnetic field (H ≥ 4 T) along the [111] direction is revealed, which is not observed when the magnetic field is applied along the [100] and [110] directions. High field neutron powder diffraction measurements confirm such a change in magnetic phase, which could be ascribed to a spin reorientation in the presence of magnetic field. In conclusion, a strong magnetic anisotropy and competing magnetic interactions play a crucial role on the complex magnetic behavior in this cubic system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Competing antiferromagnetic-ferromagnetic states in a d 7 Kitaev honeycomb magnet

The Kitaev model is a rare example of an analytically solvable and physically instantiable Hamiltonian yielding a topological quantum spin liquid ground state. Here we report signatures of Kitaev spin liquid physics in the honeycomb magnet Li 3 Co 2 SbO 6 , built of high-spin d 7 (Co 2+ ) ions, in contrast to the more typical low-spin d 5 electron configurations in the presence of large spin-orbit coupling. Neutron powder diffraction measurements, heat capacity, and magnetization studies support the development of a long-range antiferromagnetic order space group of C C 2/m, below T N = 11K at μ 0 H = 0T. The magnetic entropy recovered between T = 2 and 50 K is estimated to be 0.6Rln2, in good agreement with the value expected for systems close to a Kitaev quantum spin liquid state. The temperature-dependent magnetic order parameter demonstrates a β value of 0.19(3), consistent with XY anisotropy and in-plane ordering, with Ising-like interactions between layers. Further, we observe a spin-flop-driven crossover to ferromagnetic order with space group of C2/m under an applied magnetic field of μ 0 H ≈ 0.7T at T = 2K. Magnetic structure analysis demonstrates these magnetic states are competing at finite applied magnetic fields even below the spin-flop transition. Both the d 7 compass model, a quantitative comparison of the specific heat of Li 3 Co 2 SbO 6 , and related honeycomb cobaltates to the anisotropic Kitaev model further support proximity to a Kitaev spin liquid state. Furthermore, this material demonstrates the rich playground of high-spin d 7 systems for spin liquid candidates and complements known d 5 Ir- and Ru-based materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Antiferromagnetism and crystalline electric field excitations in tetragonal NaCeO 2

In this work, we investigate the crystal structure, magnetic properties, and crystalline electric field of tetragonal, I 4 1 / a m d , Na Ce O 2 . In this compound, Ce 3 + ions form a tetragonally elongated diamond lattice coupled by antiferromagnetic interactions ( Θ CW = - 7.69 K) that magnetically order below T N = 3.18 K. The Ce 3 + J = 5 / 2 crystalline electric field-split multiplet is studied via inelastic neutron scattering to parametrize a J eff = 1 / 2 ground state doublet composed of states possessing mixed | m z ) character. Neutron powder diffraction data reveal the onset of A -type antiferromagnetism with μ = 0.57 ( 2 ) μ B moments aligned along the c axis. The magnetic structure is consistent with the expectations of a frustrated Heisenberg J 1 - J 2 model on the elongated diamond lattice with effective exchange values J 1 > 4 J 2 and J 1 > 0 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Local structure of Mott insulating iron oxychalcogenides La 2 O 2 Fe 2 OM2(M=S,Se)

Here, we describe the local structural properties of the iron oxychalcogenides, La 2 O 2 Fe 2 OM 2 (M=S,Se), by using pair distribution function analysis applied to total scattering data. Our results from neutron powder diffraction show that M = S and Se possess similar nuclear structures at low and room temperatures. The local crystal structures were studied by investigating deviations in atomic positions and the extent of the formation of orthorhombicity. Analysis of the total scattering data suggests that buckling of the Fe 2 O plane occurs below 100 K. The buckling may occur concomitantly with a change in octahedral height. Furthermore, within a typical range of 1-2 nm, we observed a short-range orthorhombiclike structure suggestive of nematic fluctuations in both of these materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Competing energetic states in γ – Fe 2 W O 6 with strong spin-charge-lattice coupling

We report magnetic and electronic properties of γ – Fe 2 W O 6 via neutron powder-diffraction measurements and first-principles density-function theory calculations. We reveal a magnetic ground state with two phases coexisting in which the minor phase is the same as an earlier report, despite the fact that both materials studied have the same space group but with slightly different atomic positions. Interestingly, both magnetic phases are well captured by first-principles calculations. Furthermore, we show that these two magnetic phases are correlated with electronic properties, with one being insulating and the other being metallic. These features suggest that γ – Fe 2 W O 6 exhibits competing energetic states in which spin, charge, and lattice degrees of freedom are strongly coupled to each other.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Noncollinear spin structure with weak ferromagnetism in NbMnP

NbMnP is a metallic material, which consists of the zigzag chains of Mn moments along the b axis. The magnetic susceptibility as well as the resistivity shows an anomaly at 233 K, which indicates an antiferromagnetic phase transition. Our neutron powder diffraction experiment reveals that the magnetic structure is a Q=0 structure and noncollinear with an easy plane anisotropy perpendicular to the b axis, and the a- and c-axis magnetic components align antiferromagnetically and ferromagnetically along the zigzag chain direction, respectively. The ordered moment is 1.2μ B , which is reduced probably due to the itineracy of the Mn moments. A localized picture model suggests that the Q=0 magnetic structure is formed by the frustration among several exchange couplings. A weak ferromagnetic component is also present in the antiferromagnetic phase, which is considered to be caused by a Dzyaloshinskii-Moriya interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Physical properties of the quasi-two-dimensional square lattice antiferromagnet Ba 2 FeSi 2 O 7

In this work, we report magnetization (χ, M ), magnetic specific heat ( C M ), and neutron powder diffraction results on a quasi-two-dimensional (2D) S = 2 square lattice antiferromagnet Ba 2 FeSi 2 O 7 consisting of FeO 4 tetrahedrons with highly compressive tetragonal distortion (27%). Despite of the quasi-2D lattice structure, both χ and C M present three-dimensional magnetic long-range ordering below the Néel temperature T N = 5.2 K . Neutron diffraction data show a collinear Q m = (1,0,1/2) antiferromagnetic (AFM) structure below T N but the ordered moment aligned in the a b plane is suppressed by 26% from the ionic spin S = 2 value ( 4 μ B ). Both the AFM structure and the suppressed moments are well explained by using Monte Carlo simulations with a large single-ion in-plane anisotropy D = 1 .4 meV and a rather small Heisenberg exchange J intra = 0 .15 meV in the plane. The characteristic 2D spin fluctuations are recognized in the magnetic entropy release and diffuse scattering above T N . This new quasi-2D magnetic system also displays unusual nonmonotonic dependence of T N as a function of magnetic field H .

36 MATERIALS SCIENCE↗
DOE OSTI2022

High-pressure structural systematics of dysprosium metal compressed in a neon pressure medium to 182 GPa

Here we present an experimental and theoretical study of dysprosium metal compressed in the soft pressure transmitting medium Ne up to 182 and 300 GPa, respectively. Angle-dispersive x-ray powder diffraction data from each of the high-pressure polymorphs shows anisotropic compression behavior indicating changes to the electron density distribution throughout its polymorphic landscape. We compare the monoclinic (mC4) and orthorhombic (oF16) structures for the collapsed structure for Dy above 82 GPa and verify that the oF16 structure offers a better fit to our data than the previously reported mC4 structure. Further, we have found that the oF16 structure undergoes similar anisotropic compression of its lattice parameters, with a turning point above 160 GPa; suggesting a potential phase transition at pressures much higher than achieved in this study. Density functional theory calculations show the likely candidate for this new high-pressure phase is the isosymmetric oF8 structure, which is predicted to be lower in energy than the oF16 structure above 275 GPa.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Interwoven atypical quantum states in CeLiBi 2

Here we report the discovery of CeLiBi 2 , the first example of a material in the tetragonal CeTX 2 ( T = transition metal; X = pnictogen) family wherein an alkali cation replaces the typical transition metal. Magnetic susceptibility and neutron powder diffraction measurements are consistent with a crystal-field Γ 6 ground-state Kramers doublet that orders antiferromagnetically below T N = 3.4 K with an incommensurate propagation wave vector k = ( 0, 0.0724(4), 0.5) that generates a nanometric modulation of the magnetic structure. The best model of the ordered state is an elliptical cycloid with Ce moments primarily residing in the ab plane. This is highly unusual, as all other Γ 6 CeTX 2 members order ferromagnetically. Further, we observe an atypical hard-axis metamagnetic transition at 2 T in magnetostriction, magnetization, and resistivity measurements. CeLiBi 2 is a rare example of a highly conductive material with dominant skew scattering leading to a large anomalous Hall effect. Quantum oscillations with five frequencies arise in magnetostriction and magnetic susceptibility data to T = 30 K and μ 0 H = 55 T, which indicate small Fermi pockets of light carriers with effective masses as low as 0.07 m e . Density functional theory calculations indicate that square-net Dirac-like Bi-p bands are responsible for these ultralight carriers. Together, our results show that CeLiBi 2 enables multiple atypical magnetic and electronic properties in a single clean material.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing putative orbital differentiation effects via Eu 2+ spin dynamics in Sr 1-x Eu x Fe 2 As 2

Here, in this work, we report x-ray powder diffraction, elemental analysis, electrical resistivity, magnetic susceptibility, specific heat, and electron spin resonance (ESR) in single crystals of Sr 1-x Eu x Fe 2 As 2 . We observed a breakdown of the previously reported scaling between the Eu 2+ Korringa relaxation rate obtained from ESR and the spin density wave temperature evolution for Sr-rich samples. This result suggests a distinct evolution of the orbital differentiation of the Fe 3d bands along the Sr-based series when compared to the Ba counterpart. We argue that this difference is related to a larger splitting between the structural (tetragonal-to-orthorhombic) and the Fe-driven spin density wave transitions induced by Eu doping in this series. In fact, our results indicate that the two transitions follow an opposite x-Eu dependence for Sr-concentrated samples. Our work shows that Sr 1-x Eu x Fe 2 As 2 series and the comparison with their Ba-based counterparts are exciting platforms to be explored for understanding the interplay among orbital differentiation, magnetism, and structural distortions in the iron pnictides

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Weak trimerization in the frustrated two-dimensional triangular Heisenberg antiferromagnet Lu y Y 1-y MnO 3

To understand the 2D triangular Heisenberg antiferromagnetic system, we investigated the magnetic structures and the dynamics of Lu y Y 1-y MnO 3 in detail. The substitutions are adjusted to the Mn atomic position close to x Mn =$\frac{1}{3}$. The neutron powder diffraction data claims that the magnetic structure of Lu y Y 1-y MnO 3 is described as a mixture of Γ 3 (P6' 3 cm') and Γ 4 (P6' 3 c'm) at the x Mn position for y=0.15, 0.30, and 0.45. The ratio of Γ 3 and Γ 4 depends on temperature and composition and the fraction of Γ 3 increases upon cooling, while no clear trimerization was observed at the xMn position. We estimated exchange parameters from the analysis of the low-energy part of the spin waves. The results showed a weak trimerization effect on cooling because the nearest-neighbor exchange interaction is slightly enhanced. The temperature dependence of the spin-wave dispersion around the Γ point shows that the spin gap closes with increasing temperature because the exchange interactions in the nearest Mn-Mn neighbor become smaller. Gapless diffusive magnetic excitation from a Mn triangular lattice has been observed in a wide range in Q and E space of Lu y Y 1-y MnO 3 . We found that Lu 0.3 Y 0.7 MnO 3 could be an ideal case to investigate the trimerization, frustrated magnetism, and magnetoelastic coupling often observed in two-dimensional triangular lattice Heisenberg antiferromagnet systems.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Magnetic structure and magnetoelectric coupling in the antiferromagnet Co 5⁢ (Te⁢O 3 ) 4 ⁢Cl 2

The van der Waals (vdW) layered multiferroics, which host simultaneous ferroelectric and magnetic orders, have attracted attention not only for their potentials to be utilized in nanoelectric devices and spintronics, but also offer alternative opportunities for emergent physical phenomena. To date, the vdW layered multiferroic materials are still very rare. In this work, we have investigated the magnetic structure and magnetoelectric (ME) effects in Co 5 ⁢(Te⁢O 3 ) 4 ⁢Cl 2 , a promising multiferroic compound with antiferromagnetic (AFM) Néel point T N ~18 K. The neutron-powder diffraction reveals the noncoplanar AFM state with preferred Néel vector along the c axis, while a spin reorientation occurring between 8 and 15 K is identified, which results from the distinct temperature dependence of the nonequivalent Co site's moment in Co 5 ⁢(Te⁢O 3 ) 4 ⁢Cl 2 . Moreover, it is found that Co 5 ⁢(Te⁢O 3 ) 4 ⁢Cl 2 is one of the best vdW multiferroics studied so far in terms of the multiferroic performance. The measured linear ME coefficient exhibits the emergent oscillation dependence of the angle between magnetic field and electric field, and the maximal value is as big as 45 ps/m. Finally, it is suggested that Co 5 ⁢(Te⁢O 3 ) 4 ⁢Cl 2 is an appreciated platform for exploring the emergent multiferroicity in vdW layered compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Magnon gap tuning in lithium-doped MnTe

Manganese telluride (MnTe) is a prospective platform for ultrafast carrier dynamics, spin-based thermoelectrics, and magnon-drag transport due to its unique electronic and magnetic properties. We use inelastic neutron scattering to study both pure and lithium-doped MnTe, focusing on the influence of doping in opening a magnon gap. We use neutron powder diffraction to determine critical exponents for the phase transition in both pure and Li-doped MnTe and complement this information with muon spin rotation/relaxation. In conclusion, the opening of the magnon gap and spin reorientation in Li-doped MnTe is mainly due to increased magnetic anisotropy along the [001] axis, a feature not present in pure MnTe.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Electronic and magnetic structures of a mixed triple perovskite: Ba 3 NiRuIrO 9

In search of spin-orbit coupling driven nonmagnetic J = 0 ground state and excitonic magnetism, various pentavalent iridates have been studied in recent years. However, a finite moment was observed in most of the cases due to solid state effects. Here, in this work, we investigate the electronic and magnetic structure of 6H hexagonal compound Ba 3 NiRuIrO 9 , where Ir 5+ is present along with magnetic Ni 2+ and Ru 5+ ions. Magnetic susceptibility measurements and neutron powder diffraction (NPD) experiments demonstrate the appearance of short-range magnetic ordering below 170 K and a long-range antiferromagnetic ordering below 80 K. The refinement of the NPD pattern further shows that the Ru and Ir moments interact antiferromagnetically within the dimer and interact ferromagnetically with the Ni sublattice. These experimental findings have been complemented by first-principles density functional theory calculations incorporating spin-orbit coupling effects and electronic correlations for the transitional metal d states. The computed magnetocrystalline anisotropy is also found to be significant and the crystallographic c axis comes out to be the easy axis of magnetization, consistent with the spin alignment direction found from NPD. This study shows that the mixed ruthenate iridate triple perovskite series is a promising family to study the interplay among spin-orbit coupling, electron correlation, and electron filling as a variety of Ba 3 M RuIrO 9 with M as a transition metal ion, rare-earth ion, and alkali metal ions can be synthesized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

High-pressure structural behavior of silicon telluride Si2Te3 nanoplates

The high-pressure behavior of silicon telluride (Si2Te3), a two-dimensional (2D) layered material, was investigated using synchrotron x-ray powder diffraction in a diamond anvil cell to 11.5GPa coupled with first-principles theory. Si2Te3 undergoes a phase transition at <1GPa from a trigonal to a hexagonal crystal structure. At higher pressures (>8.5GPa), x-ray diffraction showed the appearance of new peaks possibly coincident with a new phase transition, though we suspect Si2Te3 retains a hexagonal structure. Density functional theory calculations of the band structure reveal metallization above 9.1GPa consistent with previous measurements of the Raman spectra and disappearance of color and transparency at pressure. The theoretical Raman spectra reproduce the prominent features of the experiment, though a deeper analysis suggests that the orientation of Si dimers dramatically influences the vibrational response. Given the complex structure of Si2Te3, simulation of the resulting high-pressure phase is complicated by disordered vacancies and the initial orientations of Si–Si dimers in the crushed layered phase.

Li, Bohan↗
DOE OSTI2013

Dy-V magnetic interaction and local structure bias on the complex spin and orbital ordering in Dy₁₋ x Tb x VO₃ (x=0 and 0.2)

The spin and orbital ordering in Dy₁₋ x Tb x VO₃ (x=0 and 0.2) was studied by measuring x-ray powder diffraction, magnetization, specific heat, and neutron single-crystal diffraction. The results show that G-OO/C-AF and C-OO/G-AF phases coexist in Dy 0.8 Tb 0.20 VO 3 in the temperature range 2–60 K, and the volume fraction of each phase is temperature and field dependent. The ordering of Dy moments at T* = 12 K induces a transition from G-OO/C-AF to a C-OO/G-AF phase. Magnetic fields suppress the long-range order of Dy moments and thus the C-OO/G-AF phase below T*. The polarized moments induced at the Dy sublattice by external magnetic fields couple to the V 3d moments, and this coupling favors the G-OO/C-AF state. Also discussed is the effect of the Dy-V magnetic interaction and local structure distortion on the spin and orbital ordering in Dy₁₋ x Tb x VO₃.

Yan, J.-Q.↗
DOE OSTI2014

Characterization of magnetic properties of Sr 2 CuWO 6 and Sr 2 CuMoO 6

In this work we examine the low-temperature magnetic properties of the two double-perovskite compounds Sr2CuWO6 and Sr2CuMoO6 using magnetic susceptibility, muon spin rotation and relaxation, and neutron powder diffraction measurements. Additionally, the most relevant spin exchange interaction constants are derived from ab initio electronic structure calculations, aided by x-ray absorption spectroscopy. The compounds exhibit quasi-two-dimensional magnetic properties, with broad maxima at T-max = 83 and 95 K for Sr2CuWO6 and Sr2CuMoO6, respectively. However, three-dimensional long-range order takes place below T-N = 24(1) and 28(2) K for Sr2CuWO6 and Sr2CuMoO6, respectively. Our results show that the low-dimensional magnetic correlations are mainly due to the significant next-nearest-neighbor interactions in the ab plane of the double-perovskite structure, whereas three-dimensional long-range magnetic order is caused by weaker next-nearest-neighbor interactions along the c axis. Next-nearest-neighbor interactions are also slightly frustrated by weaker nearest-neighbor interactions within the ab plane. Based on these results we predict the low-temperature magnetic structure in these compounds to be type-II antiferromagnetic order of the double-perovskite lattice.

Vasala, Sami↗
DOE OSTI2014

Magnetic ordering in the frustrated J 1 - J 2 Ising chain candidate BaNd 2 O 4

The AR 2 O 4 family (R = rare earth) has recently been attracting interest as a new series of frustrated magnets, with the magnetic R atoms forming zigzag chains running along the c axis. In this paper, we have investigated polycrystalline BaNd 2 O 4 with a combination of magnetization, heat-capacity, and neutron powder diffraction measurements. Magnetic Bragg peaks are observed below T N = 1.7 K, and they can be indexed with a propagation vector of k = (0,1/2,1/2). The signal from magnetic diffraction is well described by long-range ordering of only one of the two types of Nd zigzag chains, with collinear up-up-down-down intrachain spin configurations (double Néel state). Furthermore, low-temperature magnetization and heat-capacity measurements reveal two magnetic-field-induced spin transitions at 2.75 and 4 T for T = 0.46 K. The high-field phase is paramagnetic, while the intermediate-field state may arise from a spin transition of the long-range ordered Nd chains. Finally, one possible candidate for the field-induced ordered state corresponds to an up-up-down intrachain spin configuration, as predicted for a classical J 1 -J 2 Ising chain with a double Néel ground state in zero field.

36 MATERIALS SCIENCE↗