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At least 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Structural and magnetic properties of CoTeMo⁢O 6

Here, we have conducted a comprehensive investigation into the magnetic properties of the chiral multiferroic material CoTeMo⁢O 6 . In contrast with the previous claim of canted antiferromagnetic order with ferromagnetic components [Y. Doi et al., J. Solid State Chem. 182, 3232 (2009)], our investigation reveals an antiferromagnetic ground state with compensated moments, providing an interesting platform for exploring exotic material properties. Through careful measurements of magnetization under a series of applied fields, we demonstrate that there exist two sequential field-induced magnetic transitions in CoTeMo⁢O 6 , with one occurring at 𝐻 𝑐⁢1 =460 Oe along the 𝑎 axis, and the other at 𝐻 𝑐⁢2 =1.16 T with the field along the 𝑏 axis. The values of 𝐻 𝑐⁢1 and 𝐻 𝑐⁢2 exhibit strong angular dependence and diverge with different rates as the applied field is rotated 90 ° within the 𝑎⁢𝑏 plane. This reflects the distinct nature of these transitions, which is further supported by the different critical behavior of 𝐻 𝑐⁢1 and 𝐻 𝑐⁢2 , characterized by the values of 𝛾, in the function of 𝐻 𝑐 =𝐻 0 ⁡(1−𝑇/𝑇 𝑐 ) 𝛾 . Furthermore, we have demonstrated that there exist structural and magnetic twin domains in CoTeMo⁢O 6 that strongly affect the experimental measurement of their macroscopic properties. Intriguingly, these twin domains can be related to the orthorhombicity/chirality of the crystal structure with the space group 𝑃⁢2 1 ⁢2 1⁢ 2. We further explored the magnetic and structural domains with uniaxial pressure and polarized light microscopy. Our results suggest that CoTeMo⁢O 6 could be used as a unique platform for investigating the intriguing physics involving intertwined degrees of freedom. The tunability of the underlying domain distribution and its strong anisotropy could also be useful for developing functional devices and applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Correlation between complex spin textures and the magnetocaloric and Hall effects in Eu⁢(Ga 1−𝑥 ⁢Al 𝑥 ) 4 (𝑥=0.9, 1)

Determining the electronic phase diagram of a quantum material as a function of temperature (𝑇) and applied magnetic field (𝐻) forms the basis for understanding the microscopic origin of transport properties, such as the anomalous Hall effect (AHE) and topological Hall effect (THE). For many magnetic quantum materials, including Eu⁢Al 4 , a THE arises from a topologically protected magnetic skyrmion lattice with a nonzero scalar spin chirality. We identified a square skyrmion lattice (sSkL) peak in Eu⁢(Ga 1−𝑥 ⁢Al 𝑥 ) 4 (𝑥=0.9) identical to the peak previously observed in Eu⁢Al 4 by performing neutron-scattering measurements throughout the phase diagram. Here, comparing these neutron results with transport measurements, we found that in both compounds the maximal THE does not correspond to the sSkL area. Instead of the maximal THE, the maximal magnetocaloric-effect boundaries better identify the sSkL lattice phase observed by neutron-scattering measurements. The maximal THE therefore arises from interactions of itinerant electrons with frustrated spin fluctuations in a topologically trivial magnetic state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Field-dependent magnetization of BiFeO 3 in ultrathin La 0.7 Sr 0.3 MnO 3 /BiFeO 3 superlattice

We report the observation of field-induced magnetization of BiFeO 3 (BFO) in an ultrathin La 0.7 Sr 0.3 MnO 3 (LSMO)/BFO superlattice using polarized neutron reflectivity (PNR). The depth dependent structure and magnetic characterization of subnano layer thick (thickness ~ 0.7 nm each) LSMO/BFO hetrostructure is carried out using X-ray reflectivity and PNR techniques. Our PNR results indicate parallel alignment of magnetization as well as enhancement in magnetic moment across LSMO/BFO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. As a result, we observed a saturation magnetization of 110 ± 15 kA/m (~0.8 μ B /Fe) for ultrathin BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell).

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2016

Structure and magnetic properties of L n MnSbO ( L n = La and Ce)

Here, a neutron powder diffraction (NPD) study of LnMnSbO (Ln = La or Ce) reveals differences between the magnetic ground state of the two compounds due to the strong Ce-Mn coupling compared to La-Mn. The two compounds adopt the P4/nmm space group down to 2 K, and whereas magnetization measurements do not show obvious anomaly at high temperatures, NPD reveals a C-type antiferromagnetic (AFM) order below T N = 255K for LaMnSbO and 240 K for CeMnSbO. While the magnetic structure of LaMnSbO is preserved to base temperature, a sharp transition at T SR = 4.5K is observed in CeMnSbO due to a spin-reorientation (SR) transition of the Mn 2+ magnetic moments from pointing along the c axis to the ab plane. The SR transition in CeMnSbO is accompanied by a simultaneous long-range AFM ordering of the Ce moments, which indicates that the Mn SR transition is driven by the Ce-Mn coupling. The ordered moments are found to be somewhat smaller than those expected for Mn 2+ (S = 5/2) in insulators, but large enough to suggest that these compounds belong to the class of local-moment antiferromagnets. The lower T N found in these two compounds compared to the As-based counterparts (T N = 317 for LaMnAsO, T N = 347K for CeMnAsO) indicates that the Mn-Pn (Pn=As or Sb) hybridization that mediates the superexchange Mn-Pn-Mn coupling is weaker for the Sb-based compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Fragile singlet ground-state magnetism in the pyrochlore osmates R 2 Os 2 O 7 ( R = Y and Ho)

The singlet ground state magnetism in pyrochlore osmates Y 2 Os 2 O 7 and Ho 2 Os 2 O 7 is studied by DC and AC susceptibility, specific heat, and neutron powder diffraction measurements. Despite the expected non-magnetic singlet in the strong spin-orbit coupling (SOC) limit for Os 4+ (5d 4 ), Y 2 Os 2 O 7 exhibits a spin-glass (SG) ground state below 4 K with weak magnetism, suggesting possible proximity to a quantum phase transition between the non-magnetic state in the strong SOC limit and the magnetic state in the strong superexchange limit. Ho 2 Os 2 O 7 has the same structural distortion as occurs in Y 2 Os 2 O 7 . However, the Os sublattice in Ho 2 Os 2 O 7 shows long- range magnetic ordering below 36 K. We find that the sharp difference of the magnetic ground state between Y 2 Os 2 O 7 and Ho 2 Os 2 O 7 signals the singlet ground state magnetism in R 2 Os 2 O 7 is fragile and can be disturbed by the weak 4f—5d interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural and magnetic properties of the 5d 2 double perovskites Sr 2 B ReO 6 ( B = Y, In)

With this study, we have performed magnetic susceptibility, heat capacity, neutron powder diffraction, and muon spin relaxation experiments to investigate the magnetic ground states of the 5$d^2$ double perovskites Sr$_2$YReO$_6$ and Sr$_2$InReO$_6$. We find that Sr$_2$YReO$_6$ is a spin glass, while Sr$_2$InReO$_6$ hosts a non-magnetic singlet state. By making detailed comparisons with other 5$d^2$ double perovskites, we argue that a delicate interplay between spin-orbit coupling, non-cubic crystal fields, and exchange interactions plays a key role in the great variation of magnetic ground states observed for this family of materials.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2017

Tricritical point of the f -electron antiferromagnet US b 2 driven by high magnetic fields

In pulsed magnetic fields up to 65 T and at temperatures below the Néel transition, our magnetization and magnetostriction measurements reveal a field-induced metamagneticlike transition that is suggestive of an antiferromagnetic to ferrimagnetic ordering. Our data also suggest a change in the nature of this metamagneticlike transition from second- to first-order-like near a tricritical point at T tc ~ 145K and H c ~ 52 T. At high fields for H > H c we found a decreased magnetic moment roughly half of the moment determined by neutron powder diffraction. Lastly, we propose that the decreased moment and lack of saturation at high fields indicate the presence of a field-induced ferrimagnetic state above the tricritical point of the H-T phase diagram for USb 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

G -type magnetic order in ferropnictide Cu x Fe 1–y As induced by hole doping on As sites

Strong antiferromagnetic (AFM) correlation has long been postulated to be closely related to the occurrence of unconventional high-temperature superconductivity observed in the cuprates, heavy fermions, and organic superconductors. Here, the recently discovered Fe-based superconductors add another interesting member to the list. However, insufficient attention has been paid to the versatile nature of the magnetic correlation in these materials: some showing stripe (C-type) order, others double stripe (E-type) or block AFM order instead, implying potentially richer structures of the superconducting order. Here we report the observation of yet another AFM correlation in the family: a G-type AFM order as seen in the high-T c cuprates, in Cu x Fe 1–y As compounds isostructural to the LiFeAs superconductor. This study not only sheds light on the underlying mechanism of the rich magnetic correlations in the Fe-based superconductors, but also suggests the possibility of realizing a distinct pairing symmetry upon chemical doping or applying pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Metastability and hysteretic vortex pinning near the order-disorder transition in NbSe 2 : Interplay between plastic and elastic energy barriers

We studied thermal and dynamic history effects in the vortex lattice (VL) near the order-disorder transition in clean NbSe 2 single crystals. Comparing the evolution of the effective vortex pinning and the bulk VL structure, we observed metastable superheated and supercooled VL configurations that coexist with a hysteretic effective pinning response due to thermal cycling of the system. A novel scenario, governed by the interplay between (lower) elastic and (higher) plastic energy barriers, is proposed as an explanation for our observations: Plastic barriers, which prevent the annihilation or creation of topological defects, require dynamic assistance to be overcome and to achieve a stable VL at each temperature. Conversely, thermal hysteresis in the pining response is ascribed to low energy barriers, which inhibit rearrangement within a single VL correlation volume and are easily overcome as the relative strength of competing interactions changes with temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Suppression of the commensurate magnetic phase in nanosized hübnerite MnW O 4

Magnetic structures of nanosized (20 to 70 nm) powders of MnWO 4 and MnWO 4 :Mo were studied using neutron powder diffraction (NPD). Sizes and shapes of the crystallites calculated from anisotropic peak broadening of diffraction peaks were found to be orthogonal parallelepipedlike with the longest edge along the c axis and the shortest along the b axis. SQUID measurements indicate the presence of two magnetic transitions around 8 and 12 K. Rietveld refinement of the NPD data below the magnetic transition was consistent with the presence of an incommensurate spiral-like (ac-AF2) phase. Finally, a commensurate phase AF1 was not observed down to 2.5 K for all of the samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Pressure tuning of structure, superconductivity, and novel magnetic order in the Ce-underdoped electron-doped cuprate T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 )

High-pressure neutron powder diffraction, muon-spin rotation, and magnetization studies of the structural, magnetic, and the superconducting properties of the Ce-underdoped superconducting (SC) electron-doped cuprate system with the Nd 2 CuO 4 (the so-called T ' ) structure T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 with x = 0.1 are reported. A strong reduction of the in-plane and out-of-plane lattice constants is observed under pressure. However, no indication of any pressure-induced phase transition from T' to the K 2 NiF 4 (the so-called T) structure is observed up to the maximum applied pressure of p = 11 GPa. Large and nonlinear increase of the short-range magnetic order temperature T so in T ' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1) was observed under pressure. Simultaneous pressure causes a nonlinear decrease of the SC transition temperature T c . All these experiments establish the short-range magnetic order as an intrinsic and competing phase in SC T' - Pr 1.3 - x La 0.7 Ce x CuO 4 ( x = 0.1 ). The observed pressure effects may be interpreted in terms of the improved nesting conditions through the reduction of the in-plane and out-of-plane lattice constants upon hydrostatic pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Magnetic structure of the mixed antiferromagnet NdMn 0.8 Fe 0.2 O 3

The magnetic structure of the mixed antiferromagnet NdMn 0.8 Fe 0.2 O 3 was resolved. Neutron powder diffraction data definitively resolve the Mn sublattice with a magnetic propagation vector k=(000) and with the magnetic structure (A x , F y , G z ) for 1.6 K N (≈ 59 K). The Nd sublattice has a (0, f y , 0) contribution in the same temperature interval. The Mn sublattice undergoes a spin-reorientation transition at T 1 ≈ 13 K while the Nd magnetic moment abruptly increases at this temperature. Powder x-ray diffraction shows a strong magnetoelastic effect at T N but no additional structural phase transitions from 3 to 300 K. Density functional theory calculations confirm the magnetic structure of the undoped NdMnO 3 as part of our analysis. Taken together, these results show that the magnetic structure of the Mn sublattice in NdMn 0.8 Fe 0.2 O 3 is a combination of the Mn and Fe parent compounds, but the magnetic ordering of the Nd sublattice spans a broader temperature interval than in the case of NdMnO 3 and NdFeO 3 . Lastly, this result is a consequence of the fact that the Nd ions do not order independently, but via polarization from the Mn/Fe sublattice.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Neutron and x-ray scattering study of phonon dispersion and diffuse scattering in ( Na , Bi ) Ti O 3 - x BaTi O 3 single crystals near the morphotropic phase boundary

Neutron and x-ray scattering measurements were performed on (Na 1/2 Bi 1/2 )TiO 3-x at % BaTiO 3 (NBT-xBT) single crystals (x = 4, 5, 6.5, and 7.5) across the morphotropic phase boundary (MPB), as a function of both composition and temperature, and probing both structural and dynamical aspects. In addition to the known diffuse scattering pattern near the gamma points, our measurements revealed new, faint superlattice peaks, as well as an extensive diffuse scattering network, revealing a short-range ordering of polar nanoregions (PNR) with a static stacking morphology. Furthermore, in samples with compositions closest to the MPB, our inelastic neutron scattering investigations of the phonon dynamics showed two unusual features in the acoustic phonon branches, between the superlattice points, and between the superlattice points and gamma points, respectively. Finally, these critical elements are not present in the other compositions away from the MPB, which suggests that these features may be related to the tilt modes coupling behavior near the MPB.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Mott transition controlled by lattice-orbital coupling in 3 d -metal-doped double-layer ruthenates

We have investigated unusual phase transitions that were triggered by chemical doping in Ca 3 Ru 2 O 7 . Our experiments showed that doping with a few percent of Mn (>4%) can change the quasi-two-dimensional metallic state of Ca 3 Ru 2 O 7 into a Mott insulating state with a G-type antiferromagnetic order, but this Mott state cannot be induced by Fe doping. By combining these results with first-principles calculations, we show that lattice-orbital coupling (LOC) plays an important role in the Mott transition. Interestingly, the transition temperature T MIT is found to be predetermined by a structural parameter denoted by c/√ab at temperatures far above Néel temperature T N . This LOC-assisted Mott transition clearly contrasts with the band-filling picture. It is addressed that this type of Mott transition originates in the strong scattering centers formed by specific 3d dopants. The dopant-scattering picture is then applied to explain the puzzling doping effects that occur in other ruthenates and 3d oxides. As a result, our findings will advance the general understanding of how the unusual properties of 4d correlated systems are governed by the complex interplay that occurs among the charge, spin, lattice, and orbital degrees of freedom.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Tuning the antiferromagnetic helical pitch length and nanoscale domain size in Fe 3 PO 4 O 3 by magnetic dilution

The insulating magnetic material Fe 3 PO 4 O 3 features a noncentrosymmetric lattice composed of Fe 3 + triangular units. Frustration, due to competing near-neighbor (J 1 ) and next-nearest-neighbor (J 2 ) antiferromagnetic interactions, was recently suggested to be the origin of an antiferromagnetic helical ground state with unusual needlelike nanoscale magnetic domains in Fe 3 PO 4 O 3 . Magnetic dilution is shown here to tune the ratio of these magnetic interactions, thus providing deeper insight into this unconventional antiferromagnet. Dilution of the Fe 3+ lattice in Fe 3 PO 4 O 3 was accomplished by substituting nonmagnetic Ga 3+ to form the solid solution series Fe 3-x Ga x PO 4 O 3 with x=0.012, 0.06, 0.25, 0.5, 1.0, 1.5. Magnetic susceptibility and neutron powder diffraction data from this series are presented. A continuous decrease of both the helical pitch length and the domain size is observed with increasing dilution up to at least x=0.25, while for x≥0.5, the compounds lack long-range magnetic order entirely. The decrease in the helical pitch length with increasing x can be qualitatively understood by reduction of the ratio of J 2 /J 1 in the Heisenberg model, consistent with mean-field considerations. Intriguingly, the magnetic correlation length in the ab plane remains nearly equal to the pitch length for each value of x≤0.25, showing that the two quantities are intrinsically connected in this unusual antiferromagnet.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Polarized neutron scattering study of the multiple order parameter system NdB 4 [Polarized neutron scattering study on multiple order parameter system NdB 4 ]

Neutron polarization analysis has been carried out in order to clarify the magnetic structures of multiple order parameter f-electron system NdB 4 . We confirmed the noncollinear “all-in all-out” structure (Γ 4 ) of the in-plane moment, which is in good agreement with our previous neutron powder diffraction study. We found that the magnetic moment along the c-axis m c showed diagonally antiferromagnetic structure (Γ 10 ), inconsistent with previously reported “vortex” structure (Γ 2 ). The microscopic mixture of these two structures with → q 0 =(0,0,0) appears in phase II and remains stable in phases III and IV, where an incommensurate modulation coexists. The unusual magnetic ordering is phenomenologically understood via Landau theory with the primary order parameter Γ 4 coupled with higher-order secondary order parameter Γ 10 . The magnetic moments were estimated to be 1.8 ± 0.2 and 0.2 ± 0.05μ B at T = 7.5K for Γ 4 and Γ 10 , respectively. We also found a long-period incommensurate modulation of the → q 1 =(0,0,1/2) antiferromagnetic structure of mc with the propagation → q s1 =(0.14,0.14,0.1) and → q s2 =(0.2,0,0.1) in phase III and IV, respectively. The amplitude of sinusoidal modulation was about m c =1.0 ± 0.2μ B at T=1.5 K. The local (0,0,1/2) structure consists of in-plane ferromagnetic and out-of-plane antiferromagnetic coupling of m c , opposite to the coexisting Γ 10 . The mc of Γ 10 is significantly enhanced up to 0.6μ B at T=1.5 K, which is accompanied by the incommensurate modulations. As a result, the Landau phenomenological approach indicates that the higher-order magnetic and/or multipole interactions based on the pseudoquartet f-electron state play important roles.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Emphanitic anharmonicity in PbSe at high temperature and anomalous electronic properties in the Pb Q ( Q = S , Se , Te ) system

Here, the temperature dependence of the local structure of PbSe has been investigated using pair distribution function (PDF) analysis of x-ray and neutron powder diffraction data and density functional theory (DFT) calculations. Observation of non-Gaussian PDF peaks at high temperature indicates the presence of significant anharmonicity, which can be modeled as Pb off-centering along [100] directions that grows on warming similar to the behavior seen in PbTe and PbS and sometimes called emphanisis. Interestingly, the emphanitic response is smaller in PbSe than in both PbS and PbTe indicating a nonmonotonic response with chalcogen atomic number in the PbQ (Q = S, Se, Te) series. The DFT calculations indicate a correlation between band gap and the amplitude of [100] dipolar distortion, suggesting that emphanisis may be behind the anomalous composition and temperature dependencies of the band gaps in this series.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗