High-resolution Neutron Powder Diffraction Research Articles

Effects of Fe substitution for Mn on structural, magnetic and magnetocaloric properties of TbMn2-xFexSi2

The structural and magnetic properties of TbMn2-xFexSi2 compounds (x = 0.0–0.4) have been investigated in details by high-resolution synchrotron x-ray and neutron powder diffraction, specific heat, and dc magnetization measurements. The replacement of Fe for Mn in TbMn2-xFexSi2 does not change the crystal structure but leads to a significant contraction of the unit cell (dV/dx ∼ - 6 Å3) and modification of three magnetic phase transition temperatures – the Curie temperatures Tc1, Tc2 and the Néel temperature TN. For example, the Tc1, Tc2 and TN values of TbMn2Si2 decrease from Tc1 = 50 K, Tc2 = 64 K and TN = 500 K to Tc1 = 27 K, Tc2 = 37 K and TN = 440 K for TbMn1.6Fe0.4Si2. Detailed neutron diffraction investigations have allowed us to determine the magnetic structures and construct the magnetic phase diagram as well as confirm the presence of magnetoelastic coupling effects. The significantly different responses of Tc1 and Tc2 to applied magnetic fields (e.g. dTc1/dB = 0.52 K/T and dTc2/dB = 4.7 K/T for TbMn1.6Fe0.4Si2), leads to expansion of the temperature region (ΔT = Tc2- Tc1) for the canted ferromagnetic state Fmc-ii between Tc1 and Tc2. In the case of TbMn1.6Fe0.4Si2, ΔT increases from ΔT = 9 K for applied magnetic field B = 0.2 T to ΔT = 36 K for B = 6 T, resulting in plateau-like behaviour of magnetic entropy change and enhances the relative cooling power (RCP) in this system. Under a change of magnetic field of 0 T – 5 T, the maximum value of the magnetic entropy changes -ΔSmax and adiabatic temperature change, ΔTad are derived to be -ΔSmax = 13.1 J/kg K and ΔTad = 8.4 K with the RCP = 411 J/kg for x=0.4 sample. The plateau-like magnetocaloric effect and relatively large RCP make these materials potentially suitable for application in cryogenic magnetic refrigeration.

Origin of Polarization in Bismuth Sodium Titanate-Based Ceramics.

The classical view of the structural changes that occur at the ferroelectric transition in perovskite-structured systems, such as BaTiO3, is that polarization occurs due to the off-center displacement of the B-site cations. Here, we show that in the bismuth sodium titanate (BNT)-based composition 0.2(Ba0.4Sr0.6TiO3)-0.8(Bi0.5Na0.5TiO3), this model does not accurately describe the structural situation. Such BNT-based systems are of interest as lead-free alternatives to currently used materials in a variety of piezo-/ferroelectric applications. A combination of high-resolution powder neutron diffraction, impedance spectroscopy, and ab initio calculations reveals that Ti4+ contributes less than a third in magnitude to the overall polarization and that the displacements of the O2- ions and the A-site cations, particularly Bi3+, are very significant. The detailed examination of the ferroelectric transition in this system offers insights applicable to the understanding of such transitions in other ferroelectric perovskites, particularly those containing lone pair elements.

Revisiting the structures and phase transitions of Ba2NaNb5O15.

The room-temperature and low-temperature structure(s) of Ba2NaNb5O15 (BNN) have been debated since the structure was proposed in the 1960s. This work revisits the structures and phase transitions of BNN, combining high-resolution X-ray and neutron powder diffraction with density functional theory calculations. Temperature-dependent high-resolution X-ray powder diffraction patterns are collected from 4 to 918 K, and sequential batch Rietveld refinement using a symmetry mode approach to describe the structure is used to extract the main structural changes as a function of temperature. The data show that the average structure of BNN is best described by the Ama2 space group, and no other structural phase transitions were observed below the ferroelastic transition. The symmetry mode analysis, combining results from diffraction and density functional theory, shows significant octahedral tilting and corrugations of both the A1 and A2 sites along the c direction. A strong correlation between the spontaneous strain and the octahedral tilting was observed, and a potential connection with emerging microstructure at low temperatures is proposed, all enabled by the symmetry mode approach used in this work.

Structure and thermal expansion of end-member olivines I: Crystal and magnetic structure, thermal expansion, and spontaneous magnetostriction of synthetic fayalite, Fe2SiO4, determined by high-resolution neutron powder diffraction

AbstractThe lattice parameters and the crystal and magnetic structures of Fe2SiO4 have been determined from 10 K to 1453 K by high-resolution time-of-flight neutron powder diffraction. Fe2SiO4 undergoes two antiferromagnetic phase transformations on cooling from room temperature: the first, at 65.4 K, is to a collinear antiferromagnet with moments on two symmetry-independent Fe ions; the second transition, at ~23 K, is to a structure in which the moments on one of the sets of Fe ions (those on the ‘M1 site’) become canted. The magnetic unit cell is identical to the crystallographic (chemical) unit cell and the space group remains Pbnm throughout. The magnetic structures have been refined and the results found to be in good agreement with previous studies; however, we have determined the spontaneous magnetostrictive strains, which have not been reported previously. In the paramagnetic phase of Fe2SiO4, at temperatures of 70 K and above, we find that the temperature dependence of the linear thermal expansion coefficient of the b axis takes an unusual form. In contrast to the behaviour of the expansion coefficients of the unit-cell volume and of the a and c axes, which show the expected reduction in magnitude below ~300 K, that of the b axis remains almost constant between ~70 K and 1000 K.

Polyhedral Distortions and Unusual Magnetic Order in Spinel FeMn2O4.

Spinel compounds AB2X4 consist of both tetrahedral (AX4) and octahedral (BX6) environments with the former forming a diamond lattice and the latter a geometrically frustrated pyrochlore lattice. Exploring the fascinating physical properties and their correlations with structural features is critical in understanding these materials. FeMn2O4 has been reported to exhibit one structural transition and two successive magnetic transitions. Here, we report the polyhedral distortions and their correlations to the structural and two magnetic transitions in FeMn2O4 by employing the high-resolution neutron powder diffraction. The cation distribution is found to be (Mn0.92+Fe0.13+)A(Mn3+Fe0.93+Mn0.12+)BO4. While large trigonal distortion is found even in the high-temperature cubic phase, the first-order cubic-tetragonal structural transition associated with the elongation of both tetrahedra and octahedra with shared oxygen atoms along the c axis occurs at TS ≈ 750 K, driven by the Jahn-Teller effect of the orbital active B-site Mn3+ cation. Strong magnetoelastic coupling is unveiled at TN1 ≈ 400 K as manifested by the appearance of Néel-type collinear ferrimagnetic order, an anomaly in both tetrahedral and octahedral distortions, as well as an anomalous decrease of the lattice constants c and a weak anomaly of a. Upon cooling to TN2 ≈ 65 K, it evolves to a noncollinear ferrimagnetic order accompanied by the different moments at the split magnetic sites B1 and B2. Only one-half of the B-site Mn3+/Fe3+ spins, i.e., the B2-site spins in the pyrochlore lattice, are canted, which is a unique magnetic order among spinels. The canting angle between A-site and B2-site moments is ∼25°, but the B1-site moment stays antiparallel to the A-site moment even at 10 K. This noncollinear order is accompanied by a modification of the O-B-O bond angles in the octahedra without significant change in lattice constants or tetrahedral/octahedral distortion parameters, indicating a distinct magnetoelastic coupling. We demonstrate distinct roles of the A-site and B-site magnetic cations in the structural and magnetic properties of FeMn2O4. Our study indicates that FeMn2O4 is a wonderful platform to unveil interesting magnetic order and to investigate their correlations with polyhedral distortions and lattice.

Nuclear and magnetic spin structure of the antiferromagnetic triangular lattice compound LiCrTe2 investigated by mu ^+SR, neutron and X-ray diffraction

Two-dimensional (2D) triangular lattice antiferromagnets (2D-TLA) often manifest intriguing physical and technological properties, due to the strong interplay between lattice geometry and electronic properties. The recently synthesized 2-dimensional transition metal dichalcogenide LiCrTe_2, being a 2D-TLA, enriched the range of materials which can present such properties. In this work, muon spin rotation (mu ^+SR) and neutron powder diffraction (NPD) have been utilized to reveal the true magnetic nature and ground state of LiCrTe_2. From high-resolution NPD the magnetic spin order at base-temperature is not, as previously suggested, helical, but rather collinear antiferromagnetic (AFM) with ferromagnetic (FM) spin coupling within the ab-plane and AFM coupling along the c-axis. The value if the ordered magnetic Cr moment is established as mu _{textrm{Cr}}= 2.36~mu _{textrm{B}}. From detailed mu ^+SR measurements we observe an AFM ordering temperature T_{textrm{N}}approx 125 K. This value is remarkably higher than the one previously reported by magnetic bulk measurements. From mu ^+SR we are able to extract the magnetic order parameter, whose critical exponent allows us to categorize LiCrTe_2 in the 3D Heisenberg AFM universality class. Finally, by combining our magnetic studies with high-resolution synchrotron X-ray diffraction (XRD), we find a clear coupling between the nuclear and magnetic spin lattices. This suggests the possibility for a strong magnon–phonon coupling, similar to what has been previously observed in the closely related compound LiCrO_2.

Clarification of underneath capacity loss for O3-type Ni, co free layered cathodes at high voltage for sodium ion batteries

Earth abundant O3-type NaFe0.5Mn0.5O2 layered oxide is regarded as one of the most promising cathodes for sodium ion batteries due to its low cost and high energy density. However, its poor structural stability and cycle life strongly impede the practical application. Herein, the dynamic phase evolution as well as charge compensation mechanism of O3-type NaFe0.5Mn0.5O2 cathode during sodiation/desodiation are revealed by a systemic study with operando X-ray diffraction and X-ray absorption spectroscopy, high resolution neutron powder diffraction and neutron pair distribution functions. The layered structure experiences a phase transition of O3 → P3 → OP2 → ramsdellite during the desodiation, and a new O3′ phase is observed at the end of the discharge state (1.5 V). The density functional theory (DFT) calculations and nPDF results suggest that depletion of Na+ ions induces the movement of Fe into Na layer resulting the formation of an inert ramsdellite phase thus causing the loss of capacity and structural integrity. Meanwhile, the operando XAS clarified the voltage regions for active Mn3+/Mn4+ and Fe3+/Fe4+ redox couples. This work points out the universal underneath problem for Fe-based layered oxide cathodes when cycled at high voltage and highlights the importance to suppress Fe migration regarding the design of high energy O3-type cathodes for sodium ion batteries.

Ab initio simulations of α- and β-ammonium carbamate (NH4·NH2CO2), and the thermal expansivity of deuterated α-ammonium carbamate from 4.2 to 180 K by neutron powder diffraction.

Experimental and computational studies of ammonium carbamate have been carried out, with the objective of studying the elastic anisotropy of the framework manifested in (i) the thermal expansion and (ii) the compressibility; furthermore, the relative thermodynamic stability of the two known polymorphs has been evaluated computationally. Using high-resolution neutron powder diffraction data, the crystal structure of α-ammonium carbamate (ND4·ND2CO2) has been refined [space group Pbca, Z = 8, with a = 17.05189 (15), b = 6.43531 (7), c = 6.68093 (7) Å and V = 733.126 (9) Å3 at 4.2 K] and the thermal expansivity of α-ammonium carbamate has been measured over the temperature range 4.2-180 K. The expansivity shows a high degree of anisotropy, with the b axis most expandable. The ab initio computational studies were carried out on the α- and β-polymorphs of ammonium carbamate using density functional theory. Fitting equations of state to the P(V) points of the simulations (run athermally) gave the following values: V0 = 744 (2) Å3 and bulk modulus K0 = 16.5 (4) GPa for the α-polymorph, and V0 = 713.6 (5) Å3 and K0 = 24.4 (4) GPa for the β-polymorph. The simulations show good agreement with the thermoelastic behaviour of α-ammonium carbamate. Both phases show a high-degree of anisotropy; in particular, α-ammonium carbamate shows unusual compressive behaviour, being determined to have negative linear compressibility (NLC) along its a axis above 5 GPa. The thermodynamically stable phase at ambient pressure is the α-polymorph, with a calculated enthalpy difference with respect to the β-polymorph of 0.399 kJ mol-1; a transition to the β-polymorph could occur at ∼0.4 GPa.

The magnetic structure of DyFeO3 revisited: Fe spin reorientation and Dy incommensurate magnetic order

High resolution and high intensity neutron powder diffraction is used to study the ground state magnetic order and the spin reorientation transition in the orthoferrite DyFeO3. The transition from the high temperature k = 0 Γ4 (G x A y F z ) to the low temperature Γ1 (A x G y C z ) type order of the Fe-sublattice is found at T SR = 73 K and does not show any thermal hysteresis. Below T N2 = 4 K the Dy-sublattice orders in an incommensurate magnetic structure with k = [0, 0, 0.028] while the Fe-sublattice keeps its commensurate Γ1 type order. DyFeO3 is the first orthoferrite RFeO3 to possess an incommensurate magnetic order of the rare earth sublattice under zero field conditions; an important piece of information neglected in the recent discussion of its multiferroic properties.

Cation Disorder and Large Tetragonal Supercell Ordering in the Li-Rich Argyrodite Li7Zn0.5SiS6.

A tetragonal argyrodite with >7 mobile cations, Li7Zn0.5SiS6, is experimentally realized for the first time through solid state synthesis and exploration of the Li–Zn–Si–S phase diagram. The crystal structure of Li7Zn0.5SiS6 was solved ab initio from high-resolution X-ray and neutron powder diffraction data and supported by solid-state NMR. Li7Zn0.5SiS6 adopts a tetragonal I4 structure at room temperature with ordered Li and Zn positions and undergoes a transition above 411.1 K to a higher symmetry disordered F43m structure more typical of Li-containing argyrodites. Simultaneous occupation of four types of Li site (T5, T5a, T2, T4) at high temperature and five types of Li site (T5, T2, T4, T1, and a new trigonal planar T2a position) at room temperature is observed. This combination of sites forms interconnected Li pathways driven by the incorporation of Zn2+ into the Li sublattice and enables a range of possible jump processes. Zn2+ occupies the 48h T5 site in the high-temperature F43m structure, and a unique ordering pattern emerges in which only a subset of these T5 sites are occupied at room temperature in I4 Li7Zn0.5SiS6. The ionic conductivity, examined via AC impedance spectroscopy and VT-NMR, is 1.0(2) × 10–7 S cm–1 at room temperature and 4.3(4) × 10–4 S cm–1 at 503 K. The transition between the ordered I4 and disordered F43m structures is associated with a dramatic decrease in activation energy to 0.34(1) eV above 411 K. The incorporation of a small amount of Zn2+ exercises dramatic control of Li order in Li7Zn0.5SiS6 yielding a previously unseen distribution of Li sites, expanding our understanding of structure–property relationships in argyrodite materials.

Temperature-driven order-disorder structural transition in the oxygen sub-lattice and the complex superstructure of the high-temperature polymorph of CaSrZn2Ga2O7.

Structural order-disorder plays a decisive role in the physical properties of materials, such as magnetism, second-order harmonic generation, and ionic conductivity, and it is thus widely utilized to manipulate the crystal structure and understand structure-property correlations. Herein, we report the structural polymorphism, complex crystal structure and temperature-driven irreversible order-disorder phase transition of the polar oxides (Sr1-xCax)SrZn2Ga2O7. The low-temperature (LT) structure crystallizes in Pna21 with partial Zn/Ga ordering. Upon heating, (Sr1-xCax)SrZn2Ga2O7 undergoes an irreversible phase transition from orthorhombic Pna21 to hexagonal P63. Interestingly, the high-temperature (HT) P63 structure possesses an unexpected 3/2-fold superstructure rather than a substructure of the low-temperature (LT) Pna21 structure, which is a rare structural phenomenon in solid-state chemistry. This new HT superstructure is the most complex one in this series of oxides with 21 crystallographically independent sites determined accurately by a combination of the maximum entropy method and Rietveld refinement against high-resolution neutron powder diffraction data. In terms of the mechanism, this is a temperature-driven order-to-disorder transition in the oxygen sublattice. A careful structural analysis revealed that the oxygen disordering mainly occurs in the [SrO3] layers of the HT structure and it can be understood as respective clockwise and anticlockwise rotations of distinct GaO4-tetrahedra along the c-axis. Alternating current electrochemical impedance spectroscopic analysis revealed that the oxygen disordering in the HT structure is incapable of giving rise to oxide ionic conductivity but does lead to increased electronic conduction compared to the LT structure. The optical properties of the CaSrZn2Ga2O7 and Sr2Zn2Ga2O7 representatives are also investigated in-depth via diffuse reflectance spectroscopy and theoretic calculations.

Structural phase transition in cobalt oxyfluoride Co3Sb4O6F6 observed by high-resolution synchrotron and neutron diffraction

A structural transition was observed in non-centrosymmetric oxyfluoride Co3Sb4O6F6 at TS ∼180 K from a cubic phase (I4‾3m) to a c > a tetragonal phase (I4‾), through high-resolution neutron and synchrotron powder diffraction. In addition, specific heat, magnetization, and dielectric measurements were performed to investigate this phase transition. Although the specific heat and dielectric constant showed anomalies at TS, no transition to a ferroelectric phase was observed in the polarization hysteresis loop down to 30 K. Moreover, a magnetic structure analysis using neutron powder diffraction data revealed a transition from a paramagnetic phase to a G-type antiferromagnetic phase at TN ∼67 K, at which a peak was also observed in the specific heat measurements. The magnetic moments of Co2+ were aligned along the tetragonal c-axis with a Co2+ moment of 2.80(1) μB at 13 K. The rotation and deformation of the CoO2F4 octahedron due to the large displacement of F atoms were observed at TS from the structural analysis, which play an important role in the structural phase transition in Co3Sb4O6F6.

Disorder-Induced Structural Complexity in the Barlowite Family of S = 1/2 Kagomé Magnets

We present a comprehensive structural and magnetic characterization of the barlowite family of S = 1/2 kagomé magnets, Cu4(OH)6FX, where X = Cl, Br, or I. Through high-resolution synchrotron X-ray and neutron powder diffraction measurements, we reveal two sources of structural complexity within this family of materials, namely, compositional disorder of the halide species that occupy sites in between the kagomé layers and the positional disorder of the interlayer Cu2+ ions that persists well into the Pnma structural ground state. We demonstrate that understanding these inherent structural disorders is key as they correlate with the degree of partial order in the magnetic ground states of these quantum frustrated magnets.

Disentangling the phase sequence and correlated critical properties in Bi0.7La0.3FeO3 by structural studies

This work addresses the study of the high-temperature phase sequence of ${\mathrm{Bi}}_{0.7}{\mathrm{La}}_{0.3}{\mathrm{FeO}}_{3}$ by undertaking temperature-dependent high-resolution neutron powder diffraction (NPD) and Raman spectroscopy measurements. A determination of lattice parameters, phase fractions, and modulation wave vector was performed by Pawley refinement of the NPD data. The analysis revealed that ${\mathrm{Bi}}_{0.7}{\mathrm{La}}_{0.3}{\mathrm{FeO}}_{3}$ exhibits an incommensurate modulated orthorhombic $Pn{2}_{1}a(00\ensuremath{\gamma})000$ structure at room temperature, with a weak ferromagnetic behavior, likely arising from a canted antiferromagnetic ordering. Above ${T}_{1}=543\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, the low-temperature modulated $Pn{2}_{1}a(00\ensuremath{\gamma})000$ evolves monotonically into a fractionally growing Pnma structure up to ${T}_{\mathrm{N}}=663\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. At 663 K, the low-temperature canted antiferromagnetic phase is suppressed concurrently with the switching of the former into a nonmodulated $Pn{2}_{1}a$ structure that continues to coexist with the Pnma one, until the latter is expected to reach the 100% fraction of the sample volume at high temperatures above 733 K. The $Pn{2}_{1}a$ space group is obtained from the Pnma one through the ${\mathrm{\ensuremath{\Gamma}}}_{4}^{\ensuremath{-}}$ polar distortion. Neutron diffraction and Raman spectroscopy results provide evidence for the emergence of noteworthy linear spin-phonon coupling. In this regard, magnetostructural coupling is observed below ${T}_{\mathrm{N}}$, revealed by the relation between the weak ferromagnetism of the canted iron spins and the ${\mathrm{FeO}}_{6}$ octahedra symmetric stretching mode. The correlation between magnetization and structural results from NPD provides definite evidence for the magnetic origin of the structural modulation. The analysis of the temperature-dependent magnetization and the magnetic peak intensity as well yields a critical exponent (\ensuremath{\beta}) value of 0.38. The lower limit of the phase coexistence temperature ${T}_{1}=543\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, marking the emergence of the Pnma phase, is also associated with the temperature whereupon the modulation magnitude starts to decrease.

Synthesis, Characterization, and Crystal Structure of Dominant Uranium(V) Brannerites in the UTi2–xAlxO6 System

The synthesis, characterization, and crystal structure of a novel (dominant) uranium(V) brannerite of composition U1.09(6)Ti1.29(3)Al0.71(3)O6 is reported, as determined from Rietveld analysis of the high-resolution neutron powder diffraction data. Examination of the UTi2-xAlxO6 system demonstrated the formation of brannerite-structured compounds with varying Al3+ and U5+ contents, from U0.93(6)Ti1.64(3)Al0.36(3)O6 to U0.89(6)Ti1.00(3)Al1.00(3)O6. Substitution of Al3+ for Ti4+, with U5+ charge compensation, resulted in near-linear changes in the b and c unit cell parameters and the overall unit cell volume, as expected from ionic radii considerations. The presence of U5+ as the dominant oxidation state in near-single-phase brannerite compositions was evidenced by complementary laboratory U L3-edge and high-energy-resolution fluorescence-detected U M4-edge X-ray absorption near-edge spectroscopy. No brannerite phase was found for compositions with Al3+/Ti4+ > 1, which would require a U6+ contribution for charge compensation. These data expand the crystal chemistry of uranium brannerites to the stabilization of dominant uranium(V) brannerites by the substitution of trivalent cations, such as Al3+, on the Ti4+ site.

Structural Investigation into Magnetic Spin Orders of a Manganese Phosphatic Oxyhydroxide, Mn5[(PO4)2(PO3(OH))2](HOH)4

The ferri- and antiferromagnetic structures of a hureaulite-type synthetic compound, Mn2+5(PO4)2(PO3(OH))2(HOH)4, were elucidated by high-resolution neutron powder diffraction in combination with magnetic susceptibility and heat capacity measurements. At 6.17 K, the paramagnetic phase (space group: C2/c) transforms to inherit a ferrimagnetic order (magnetic space group: C2′/c′), followed at 1.86 K by an incommensurately modulated antiferromagnetic order (magnetic superspace group: P21/c.1′(α0γ)00s with the propagation vector k(0.523(2), 0, 0.055(1)). In the ferrimagnetic state, antiferromagnetic interactions are dominant for both intra and inter pentamers of Mn2+(O, HOH)6 octahedra. Differently aligned spin-canting sublattices seen in the ferrimagnetic models at 3.4, 4.5, and 6.1 K explain a weak ferromagnetism in the title compound. The observation of magnetic moments vigorously changing in a small temperature range of 6.1–1.5 K adumbrates a high complexity of interplaying structural and magnetic orders in this manganese phosphatic oxyhydroxide.

Evolution from sinusoidal to collinear A-type antiferromagnetic spin-ordered magnetic phase transition in Tb1−x Pr x MnO3 solid solution

The present study reports on the structural and magnetic phase transitions in Pr-doped polycrystalline Tb0.6Pr0.4MnO3, using high-resolution neutron powder diffraction (NPD) collected at SINQ spallation source, to emphasize the suppression of the sinusoidal magnetic structure of pure TbMnO3 and the evolution to a collinear A-type antiferromagnetic ordering. The phase purity, Jahn–Teller distortion, and one-electron bandwidth for eg orbital of Mn3+ cation have been calculated for polycrystalline Tb0.6Pr0.4MnO3, in comparison to the parent materials TbMnO3 and PrMnO3, through the Rietveld refinement study from x-ray diffraction data at room temperature, which reveals the GdFeO3 type orthorhombic structure of Tb0.6Pr0.4MnO3 having Pnma space group symmetry. The temperature-dependent zero field-cooled and field-cooled dc magnetization study at low temperature down to 5 K reveals a variation in the magnetic phase transition due to the effect of Pr3+ substitution at the Tb3+ site, which gives the signature of the antiferromagnetic nature of the sample, with a weak ferromagnetic component at low temperature-induced by an external magnetic field. The field-dependent magnetization study at low temperatures gives the weak coercivity having the order of 2 kOe, which is expected due to the canted-spin arrangement or ferromagnetic nature of Terbium ordering. The NPD data for Tb0.6Pr0.4MnO3 confirms that the nuclear structure of the synthesized sample maintains its orthorhombic symmetry down to 1.5 K. Also, the magnetic structures have been solved at 50 K, 25 K, and 1.5 K through the NPD study, which shows an A-type antiferromagnetic spin arrangement having the magnetic space group Pn′ma′.

Magnetic ground states of Ce3TiSb5, Pr3TiSb5 and Nd3TiSb5 determined by neutron powder diffraction and magnetic measurements

The R 3TiSb5 ternary compounds, with R a light rare earth (La to Sm) have been reported to crystallize with the anti-Hf5CuSn3-type hexagonal structure (Pearson’s symbol hP18; space-group P63/mcm, N. 193). An early article that reported possible superconductivity in some of these intermetallic phases (namely those with R = La, Ce, and Nd) caught our attention. In this work, we have now refined the crystal structure of the R 3TiSb5 compounds with R = Ce, Pr and Nd by Rietveld methods using high-resolution neutron powder diffraction data. The magnetic ground states of these intermetallics have been investigated by low-temperature magnetization and high-intensity neutron diffraction. We find two different magnetic transitions corresponding to two related magnetic structures at T N1 = 4.8 K (k 1 = [0, 1/2, 1/8]) and T N2 = 3.4 K (k 2 = [0, 0, 1/8]), respectively for Ce3TiSb5. However, the magnetic ordering appears to occur following a peculiar hysteresis: the k 2-type magnetic structure develops only after the k 1-type phase fraction has first slowly ordered with time and the size of the ordered Ce3+ magnetic moment has become large enough to induce the second magnetic transition. At T = 1.5 K the maximum amplitude of the Ce moment in the coexisting phases amounts to μ Ce = 2.15 μ B. For Nd3TiSb5 an antiferromagnetic ordering below T N = 5.2 K into a relatively simpler commensurate magnetic structure with a magnetic moment of μ Nd = 2.14(3) μ B and magnetic propagation vector of k = [0, 0, 0], was determined. No evidence of superconductivity has been found in Nd3TiSb5. Finally, Pr3TiSb5 does not show any ordering down to 1.5 K in neutron diffraction while an antiferromagnetic ground state is detected in magnetization measurements. There is no sign of magnetic contribution from Ti atoms found in any of the studied compounds.

Determination of the magnetic structures in orthoferrite CeFeO3 by neutron powder diffraction: first order spin reorientation and appearance of an ordered Ce-moment

High resolution and high intensity neutron powder diffraction are used to determine the temperature dependence of the crystallographic and magnetic structure of the orthoferrite CeFeO3. The high temperature G x -type magnetic coupling of the Fe-sublattice described by the Γ4 (G x A y F z ) irreducible representation changes at the spin reorientation temperature T SR = 228 K to a G y -type coupling of Γ1 (A x G y C z ). The spin reorientation is of first order and sees a hysteresis of about 2.5 K at T SR. Below 35 K faint magnetic peaks reflecting C z type magnetic coupling appear and are argued to be related to the Ce-sublattice. Magnetic moments at 2 K amount to μ Fe = 4.15 μ B and μ Ce = 0.11 μ B. CeFeO3 is only the second RFeO3 compound after DyFeO3 showing this ground state magnetic structure of the Fe-sublattice. The orthorhombic structure Pbnm is kept over the whole temperature range.

Uniformity of Flat Li-Ion Batteries Studied by Diffraction and Imaging of X-rays and Neutrons

A combination of high-resolution neutron powder diffraction, energy-dependent cold-neutron radiography, and synchrotron-based X-ray diffraction radiography on two pouch bag cells of different dimen...