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By using powder neutron diffraction we provide a detailed structural and magnetic investigation of the pseudo-ternary compound TbPd0.9Ni0.1Al with hexagonal ZrNiAl-type crystal structure and disorder of palladium and nickel atoms on two crystallographic sites. We provide experimental evidence for the occurrence of an isostructural phase transition in TbPd0.9Ni0.1Al at 157 K, which is affected by structural disorder compared to that observed in TbPdAl. In TbPd0.9Ni0.1Al the step of the c / a ratio at the first-order phase transition appears about four times smaller than in TbPdAl. TbPd0.9Ni0.1Al undergoes two successive magnetic phase transitions at T N 1 = 41 K and T N 2 ≈ 21.5 K. Two third of non-frustrated ordered Tb moments form commensurate antiferromagnetic chains ( k 1 = [ 1 / 2 , 0 , 1 / 2 ] ) and coexist with one third of frustrated ordered Tb moments, which change from a commensurate structure ( k 1 = [ 1 / 2 , 0 , 1 / 2 ] ) between T N 2 and T N 1 to an incommensurate structure ( k 2 i = [ 0.50 ( 1 ) , 0.12 ( 1 ) , 1 / 2 ] ) below T N 2 . Due to the strong magneto-crystalline anisotropy all ordered Tb moments stay perpendicular to the ab-plane and reach at 1.5 K saturation values of 8.6 (2) μ B (non-frustrated) and 7.2 (2) μ B (frustrated). The symmetry of the magnetic structure of TbPd0.9Ni0.1Al is lower than that of TbNiAl.

Two magnetic phase transitions have been noted for SrCoO$_{3-y}$ for near-stoichiometric oxygen concentrations (small y). Using muon spin rotation and neutron scattering experiments, we have established that the two transitions represent separate, spatially distinct magnetic phases that coexist in a two-phase equilibrium mixture. The two phases most likely represent areas of the sample with different effective valence charge density. Further, the phases exist over regions with a length scale intermediate between nanoscale charge inhomogeneity and systems such as manganites or super-oxygenated cuprates with large length scale phase separation., 5 pages, 4 figures

Magnetic frustration in three dimensions (3D) manifests itself in the spin-$\frac12$ insulator Li$_2$CuW$_2$O$_8$. Density-functional band-structure calculations reveal a peculiar spin lattice built of triangular planes with frustrated interplane couplings. The saturation field of 29 T contrasts with the susceptibility maximum at 8.5 K and a relatively low Neel temperature $T_N\simeq 3.9$ K. Magnetic order below $T_N$ is collinear with the propagation vector $(0,\frac12,0)$ and an ordered moment of 0.65(4) $\mu_B$ according to neutron diffraction data. This reduced ordered moment together with the low maximum of the magnetic specific heat ($C^{\max}/R\simeq 0.35$) pinpoint strong magnetic frustration in 3D. Collinear magnetic order suggests that quantum fluctuations play crucial role in this system, where a non-collinear spiral state would be stabilized classically.

We investigated the crystal and magnetic structures of the $\text{spin}\ensuremath{-}\frac{1}{2}$ frustrated antiferromagnet ${\mathrm{Cu}}_{3}{\mathrm{Mo}}_{2}{\mathrm{O}}_{9}$ in which the spin system consists of antiferromagnetic chains and dimers. The space group at room temperature has been reported to be orthorhombic $Pnma$ (No. 62). We infer that the space group above ${T}_{\mathrm{N}}=7.9\phantom{\rule{0.28em}{0ex}}\mathrm{K}$ is monoclinic $P{2}_{1}/m$ (No. 11) from the observation of reflections forbidden in $Pnma$ in x-ray powder diffraction experiments at room temperature. We determined the magnetic structure of ${\mathrm{Cu}}_{3}{\mathrm{Mo}}_{2}{\mathrm{O}}_{9}$ in neutron powder diffraction experiments. Magnetic moments on dimer sites lie in the $ac$ planes. The magnitudes are $(0.50\ensuremath{\sim}0.74){\ensuremath{\mu}}_{\mathrm{B}}$. Moments on chain sites may exist but the magnitudes are very small. The magnetic structure indicates that a partially disordered state is realized. We consider the origin of the magnetic structure, weak ferromagnetism, and electric polarization.

We investigated the crystal structure and lattice excitations of the ternary intermetallic stannide Ca3Ir4Sn13 using neutron and x-ray scattering techniques. For T > T* ~ 38 K the x-ray diffraction data can be satisfactorily refined using the space group Pm-3n. Below T* the crystal structure is modulated with a propagation vector of q = (1/2, 1/2, 0). This may arise from a merohedral twinning in which three tetragonal domains overlap to mimic a higher symmetry, or from a doubling of the cubic unit cell. Neutron diffraction and neutron spectroscopy results show that the structural transition at T* is of a second-order, and that it is well described by mean-field theory. Inelastic neutron scattering data point towards a displacive structural transition at T* arising from the softening of a low-energy phonon mode with an energy gap of Delta(120 K) = 1.05 meV. Using density functional theory the soft phonon mode is identified as a 'breathing' mode of the Sn12 icosahedra and is consistent with the thermal ellipsoids of the Sn2 atoms found by single crystal diffraction data.

A comparative study of four series of pyrrhotite-type chalcogenide compounds Fe(7-y)M(y)X(8) (X = S, Se) with substitution of Ti or Co for iron has been performed by means of x-ray and neutron powder diffraction, and by magnetization measurements. In Fe(7-y)M(y)X(8) compounds having a ferrimagnetic order at y = 0, the substitution of either Ti or Co for iron is observed to result in a monotonous decrease of the magnetic ordering temperature, while the resultant magnetization shows a non-monotonous behavior with a minimum around y = 1.0-1.5 in all the Fe(7-y)M(y)X(8) families except Fe(7-y)Co(y)Se(8). Suppression of a magnetically ordered state with substitutions in Fe(7-y)M(y)X(8) is ascribed to nearly zero values of Ti and Co magnetic moments, while the non-monotonous changes of the resultant magnetization are explained by the compensation of the sublattice magnetizations due to the non-random substitutions in alternating metallic layers. The difference in the cation partitioning observed in Fe(7-y)Ti(y)X(8) and Fe(7-y)Co(y)X(8) is attributed to the difference in the spatial extension of Ti and Co 3d orbitals. High coercive field values (20-24 kOe) observed at low temperatures in the Ti-containing compounds Fe(7-y)Ti(y)X(8) with y ⩾ 3 are suggested to result from the enhancement of Fe orbital moment due to the Ti for Fe substitution.

Motivated by the recent observations of incommensurate magnetic order and electric polarization in ${\mathrm{YBaCuFeO}}_{5}$ up to temperatures ${T}_{N2}$ as high as 230 K [B. Kundys et al., Appl. Phys. Lett. 94, 072506 (2009); Y. Kawamura et al., J. Phys. Soc. Jpn 79, 073705 (2010)], we report here for the first time a model for the incommensurate magnetic structure of this material, which we complement with ab initio calculations of the magnetic exchange parameters. Using neutron powder diffraction, we show that the appearance of polarization below ${T}_{N2}$ is accompanied by the replacement of the high-temperature collinear magnetic order by a circular inclined spiral with propagation vector ${\mathbf{k}}_{i}=(1/2,1/2,1/2\ifmmode\pm\else\textpm\fi{}q)$. Moreover, we find that the polarization approximately scales with the modulus of the magnetic modulation vector $q$ down to the lowest temperature investigated $(\ensuremath{\sim}3$ K). Further, we observe occupational Fe/Cu disorder in the ${\mathrm{FeO}}_{5}\text{\ensuremath{-}}{\mathrm{CuO}}_{5}$ bipyramids, although a preferential occupation of such units by Fe-Cu pairs is supported by the observed magnetic order and by density functional calculations. We calculate exchange coupling constants for different Fe/Cu distributions and show that, for those containing Fe-Cu dimers, the resulting magnetic order is compatible with the experimentally observed collinear magnetic structure $\mathrm{[}{\mathbf{k}}_{c}=(1/2,1/2,1/2),{T}_{N2}gTg{T}_{N1}=440$ K]. Based on these results, we discuss possible origins for the incommensurate modulation and its coupling with ferroelectricity.

In many materials it remains a challenge to reveal the nature of magnetic correlations, including antiferromagnetism and spin disorder. Revealing the spin structure in magnetic nanoparticles is further complicated by the large incoherent neutron scattering cross section from water adsorbed at the particle surfaces and by the broadening of diffraction peaks due to the finite crystallite size. Moreover, the spin structure in magnetic nanoparticles may deviate significantly from that of the corresponding bulk material because of the low-symmetry surroundings of surface atoms and the large relative surface contribution to the magnetic anisotropy. Here we explore the potential use of polarized neutron diffraction to reveal the magnetic structure in NiO bulk and nanoparticle powders by applying the XYZ-polarization analysis method. Our investigations address in particular the spin orientation in bulk NiO and platelet-shaped NiO nanoparticles with thickness from greater than 200 nm down to 2.0 nm. The advantage of the applied method is that it is able to clearly separate the structural, the magnetic, and the spin-incoherent scattering signals for all particle sizes. For platelet-shaped particles with thickness from greater than 200 nm down to 2.2 nm we find that the spin orientation deviates about 16 degrees from the primary (111) plane of the platelet-shaped particles. In the smallest particles (2.0 nm thick) we find the spins are oriented with a 30 degrees. average angle to the primary (111) plane of the particles. The results show that polarization analyzed neutron powder diffraction is a viable method to investigate magnetic order in powders of antiferromagnetic nanoparticles. (Less)

The layered cobaltite Sr(2)CaYCo(4)O(10.5) with formal average cobalt oxidation state close to 3+ has been studied as functions of both temperature and pressure up to 4 GPa by neutron powder diffraction (NPD). The crystal structure is shown to have tetragonal symmetry (space group I4/mmm; 2a(p) × 2a(p) × 4a(p) superstructure), and the magnetic structure at ambient pressure is found to be G-type antiferromagnetic with TN close to 310 K. The magnetic moments within the CoO(6) octahedral layers and anion-deficient CoO(4.5) layers are 1.2μ(B) and 2.8μ(B), respectively. At 25 K, and applied pressure of 3.5 GPa is sufficient to completely suppress a long-range magnetic order. This result is interpreted in terms of a pressure-induced high-to-low spin state crossover of the Co(3+) ions.

The compound TbCo 4 B was studied using measurements of AC magnetic susceptibility, magnetization and neutron powder diffraction. It is found that this compound orders at T C ≈450 K. Each of the two Tb and two Co sublattices orders ferromagnetically. The coupling is ferromagnetic within each pair and ferrimagnetic between pairs. A compensation point at ∼300 K and a spin reorientation between 400 and 430 K were found.

The influence of the low cycle fatigue parameters strain amplitude, cycle number, test temperature and frequency on the formation of martensite was investigated. Linear dependencies of the martensite content on plastic strain amplitude and the cycle number were found. The martensite content decreases exponentially with increasing temperature. No influence of LCF test frequency was found. The susceptibility for the martensitic transformation strongly depends on the thermo-mechanical pretreatment. No significant residual stresses were found after cyclic loading.

YMnO3 exhibits a ferroelectric transition at high temperature (~ 900 K) and magnetic ordering at T_N ~ 70 K where the dielectric constant shows an anomaly indicative of the magneto-dielectric effect. Here we report powder neutron diffraction experiments in this compound that show that the magnetic moment at saturation is reduced by application of hydrostatic pressure. Our results yield further insight about the nature of the spin-lattice interaction in ferroic materials.

The deuterium atom distribution in the deuterium stabilized C15-type Laves phase derivative ZrTi 2 D 4.3 has been studied by neutron powder diffraction in the temperature range 300 K T 3 -type interstices decreases from 89% at 300 K to 56% at 800 K while that of the tetrahedral Zr 2 Ti 2 -type interstices increases from 7% to 17%. The deuterium site energy difference derived from these data is ∼127 meV. Above 800 K the compound loo\ses deuterium mainly from the ZrTi 3 -type interstices while its metal atom substructure becomes partially disordered. This disorder persists after cooling to room temperature.

The modulated magnetic ordering in the multiferroic manganite CaMn 7 O 12 has been studied by using the neutron powder diffraction technique. The relative orientation of the magnetic moments of Mn 4+ and Mn 3+ ions located in Mn3 sublattice at (0,0,1/2) and Mn2 sublattice at (1/2,0,1/2) is shown to be antiparallel, i.e. their relative orientation angle Φ = π . This result differs from that given by other authors who propose another relative orientation with a value of Φ = 0.84 ( 4 ) π . The relative orientation angle is an important parameter used in model studies based on effective hamiltonians.

The volume fraction of martensite continuously increases with the fatigue cycle number. Consequently, the martensite amount can be used for indication of the low cycle fatigue state. Following an exponential decay function, the martensite volume fraction decreases with increasing temperature. No influence of the load frequency was found. The initial material state plays an important role for the martensite formation rate. The amount of martensite formed is much higher after cold-rolling than after solution annealing as final manufacturing process. The martensite shows a fibre texture in the annealed material. The (1 1 0) planes are preferentially oriented parallel and perpendicular to the loading direction. In the cold-rolled material no significant preferred orientation of this phase was found. The martensite is concentrated in the centre of the specimens. The shape of the distribution seems to be independent on the martensite amount.

The low-temperature magnetic properties of the rare-earth intermetallic compound system R3Pd20Si6(R = rare earth) were studied by elastic and inelastic neutron scattering. The compounds show due to the two rare-earth sublattices built from the 4a and 8c sites in the cubic crystal structure (space group Fm-3m) successive magnetic ordering with two different propagation vectors. In this report, we give an overview of the results obtained for the magnetic structures and the crystalline electric fields in the 3-20-6-system.

The nuclear and magnetic structures of the colossal magnetoresistive compounds Nd 0.7 Ba 0.3− y Sr y MnO 3 (0⩽ y ⩽0.2) have been investigated by means of neutron powder diffraction. For all the Ba/Sr substitutions, the nuclear structure remains orthorhombic within temperature range 1.5–293 K. However, the compound Nd 0.7 Ba 0.3 MnO 3 is characterized by the crystallographic space group Imma whereas the Sr-doped compounds crystallize in the Pnma space group. As expected from the bigger size of Ba-ion radii, the buckling as well as the distortion of MnO 6 octahedra become less pronounced when increasing the amount of Ba in Nd 0.7 Ba 0.3− y Sr y MnO 3 . In order to better understand the physical properties of these samples, these results have been included in the more general diagram Nd 0.7 A′ 0.3− y Sr y MnO 3 (A=Ca, Ba). In this series, the observed maximum in T C is not easily explained with standard parameters. Whereas the Mn magnetic moments display the same characteristics as observed in similar magnetoresistive compounds, the behavior of Nd magnetic moments shows unusual features when changing the Sr/Ba ratio in Nd 0.7 Ba 0.3 MnO 3 . In all compounds, we observe a ferromagnetic ordering of both the Nd and Mn magnetic moments along the b -axis. However, the Nd and Mn magnetic moments point in the same direction for the compounds with y ⩾0.05 but in opposite directions in Nd 0.7 Ba 0.3 MnO 3 . An important evolution of the absolute value of Nd magnetic moment at 1.5 K is also observed when changing the Sr/Ba ratio.

A novel ternary structure type has been determined from single crystals of Ce2Zn6Ge3 grown from indium?zinc flux solvent. The Ce2Zn6Ge3 type is hexagonal (a = 0.767 69(2) nm; c = 0.411 59(2) nm) with space group P 2m, Z = 1. Isotypic compounds with La, Pr, Nd, Sm and Gd were synthesized by reaction sintering, and their isotypic crystal structures were confirmed from Rietveld refinements. These novel ternaries show metallic behaviour and their ground state depends on the particular rare earth ion. Long-range magnetic order was deduced for the compounds from Ce to Gd, with a maximum transition temperature TN ~ 29 K for Gd2Zn6Ge3. While the compounds with Ce and Pr exhibit a spontaneous magnetic type of order, those with Nd, Sm and Gd are antiferromagnetic. The magnetic structures of Pr2Zn6Ge3 and Nd2Zn6Ge3 were resolved on the basis of neutron powder diffraction performed at 1.5 K.

The crystal structure of the U(Pd1−xFex)2Ge2 compounds with Fe content x = 0– 0.03 and the crystal and magnetic structure of U(Pd0.98Fe0.02)2Ge2 at high external pressures up to 4.5 GPa were studied by means of powder neutron diffraction in the temperature range 1.5–300 K. With increasing Fe content the values of the lattice parameters and interatomic distances change only slightly, but it is known from previous experiments that the magnetic structure changes drastically for x ≥ 0.015. In contrast to this, high external pressure modifies the crystal structure more significantly while the magnetic structure remains unchanged. The results obtained allow one to infer that drastic changes in the magnetic structure of the U(Pd1−xFex)2Ge2 compounds with increasing Fe content are a consequence of modification of the RKKY-type (RKKY standing for Ruderman, Kittel, Kasuya and Yosida) indirect exchange interaction due to the variation of the number of conduction electrons per U atom rather than a result of lattice contraction.

The magnetic ordering of the tetragonal (I4/mmm) HoCo 2 X 2 (X=Ge, Si) and DyCo 2 Ge 2 compounds with the ThCr 2 Si 2 type of structure has been reinvestigated by neutron powder diffraction. The HoCo 2 Si 2 compound orders exclusively with the type-I antiferromagnetic structure with the wave vector q =(0, 0, 1) and the moments confined to the c -axis, while the magnetic phase diagrams of the DyCo 2 Ge 2 and HoCo 2 Ge 2 compounds comprise three distinct regions of magnetic ordering: a low-temperature structure also of type-I ( q 1 =(0, 0, 1)), stable in the range between 2 K and T IC , a high-temperature longitudinal sine wave modulated structure with the wave vector q 2 =(0 ,0, 1− q z ), stable in the range T IC – T N and a coexistence region of q 1 and q 2 around T IC . The wave vector component q z has a temperature-dependent length and locks-in by a first-order transition to the value q z =0 at T IC . In the case of the DyCo 2 Ge 2 compound a spin reorientation transition was detected in the low-temperature range. The ordered moment values at 1.5 K are 7.8(1) μ B /Dy and 9.33(1) μ B /Ho for the RCo 2 Ge 2 compounds and 8.8(1) μ B /Ho atom for the HoCo 2 Si 2 compound at 3 K.

Specific heat, magnetic susceptibility, magnetization and neutron diffraction measurements were carried out on Ce 3 Cu 4 Sn 4 and Ce 3 Cu 4 Ge 4 compounds (structure type Gd 3 Cu 4 Ge 4 , Immm, 2 Ce sites). The linear coefficient of specific heat is γ =330 mJ/mol Ce K 2 for the stannide and γ =225 mJ/mol Ce K 2 for the germanide, indicative for heavy fermion behaviour. The Ruderman–Kittel–Kasuya–Yosida exchange interactions in the presence of the magnetocrystalline anisotropy induce magnetic ordering, which is complex and proceeds in several steps. For both compounds below the Neel temperature T N =10.3 K incommensurate magnetic arrangements are favoured. They lock into a commensurate structure with the wave vector q 3 =(0 0 0) at T 2 ( T 2 =7.3 K for stannide and T ′ 2 =7.8 K for germanide). Due to a strong anisotropy the Ce magnetic moments are aligned along the x -axis in the T 2 – T 3 interval, but at T 3 = T ′ 3 =2.6 K a reorientation of the moments into the xy -plane occurs. The evolution of the magnetic order and the moment values differ for the two inequivalent crystallographic Ce sites. The ordered Ce magnetic moment is 2.05(2) μ B at the 2d site and 1.10(2) μ B at the 4e site for germanide. For stannide the corresponding values are 0.75(1) μ B and 1.94(2) μ B . Two different magnetic arrangements are possible for Ce 3 Cu 4 Sn 4 at low temperatures.

The suppression of magnetic order with pressure concomitant with the appearance of pressure-induced superconductivity was recently discovered in CrAs. Here we present a neutron diffraction study of the pressure evolution of the helimagnetic ground state towards and in the vicinity of the superconducting phase. Neutron diffraction on polycrystalline CrAs was employed from zero pressure to 0.65 GPa and at various temperatures. The helimagnetic long-range order is sustained under pressure and the magnetic propagation vector does not show any considerable change. The average ordered magnetic moment is reduced from 1.73(2) mu(B) at ambient pressure to 0.4(1) mu(B) close to the critical pressure P-c approximate to 0.7 GPa, at which magnetic order is completely suppressed. The width of the magnetic Bragg peaks strongly depends on temperature and pressure, showing a maximum in the region of the onset of superconductivity. We interpret this as associated with competing ground states in the vicinity of the superconducting phase.

The electronic functionality of thin films is governed by their interfaces. This is very important for the ferroelectric (FE) state which depends on thin-film clamping and interfacial charge transfer. Here we show that in a heterostructure consisting of a nano-granular metal and an organic FE layer of [tetrathiafulvalene]$^{+\delta}$[p-chloranil]$^{-\delta}$ the nano-granular layer's conductance provides a sensitive and non-invasive probe of the temperature-dependent dielectric properties of the FE layer. We provide a theoretical framework that is able to qualitatively reproduce the observed conductance changes taking the anisotropy of the dielectric anomaly at the paraelectric(PE)-FE phase transition into account. The approach is also suitable for observing dynamical effects close to the phase transition. Focused electron beam induced deposition as fabrication method for the nano-granular metal guarantees excellent down-scaling capabilities, so that monitoring the FE state on the lateral scale down to 20--30\,nm can be envisioned.

The effect of high pressure exceeding 6 GPa on magnetism and multiferroicity was investigated for the olivine Mn2GeO4 that shows successive magnetic transitions at ambient pressure and a ferroelectric ground state driven by spin- spiral order. We measured heat capacity, dielectric constant, and electric polarization at various pressures using a diamond anvil cell. The pressure evolution of the magnetic structures was also investigated by powder neutron diffraction measurements using a Paris- Edinburgh press. We found that all of the magnetic transition temperatures are enhanced monotonically by applying pressure. Furthermore, the spin- driven ferroelectricity persists up to about 6 GPa but suddenly vanishes by 6.3 GPa. A consistent description of all data is achieved if an incommensurate- commensurate phase transition occurs with pressurization and causes the suppression of ferroelectricity. We discuss the origin of the observed pressure effects on the magnetism and multiferroicity in Mn2GeO4 in terms of a pressure- induced change in the superexchange magnetic interactions.

The application of percolation theory to geomaterials generally includes the study of simplified lattice models in order to derive information on pore connectivity. Here, and possibly applied for the first time to shales, we computed key percolation variables such as the percolation probability distribution from our reconstructed pore microstructures. Then, we used a finite-scaling approach to calculate the critical porosity (i.e. percolation threshold) of pore microstructures from sandy and shaley facies of Opalinus Clay. Both microstructures show anisotropic characteristics with respect to connectivity and percolation threshold. We found percolation thresholds with critical porosities 0.04 - 0.12 parallel to bedding and 0.11 - 0.19 perpendicular to bedding. The resolved porosity of the sandy facies (low clay content) is close to the percolation threshold, whereas the porosity of the shaley facies (high clay content) is below the percolation threshold. The approach yields similar results when compared to an approach that is based on morphological image techniques and involves the modification of the original pore voxel data. Therefore, we used modified pore structures in combination pore network modeling to discuss changes in gas transport properties in case porosity approaches the critical porosity from above.

Magnetic phases for the intermetallic compound NdMn1.4Co0.6Si2 have been investigated at various temperatures by dc magnetization, neutron diffraction and neutron depolarization. Our study shows multiple magnetic phase transitions with temperature (T) over 1.5-300 K. In agreement with dc-magnetization and neutron depolarization results, the temperature dependence of the neutron diffraction patterns shows five distinct regions with different magnetic phases. These temperature regions are (i) T >= 215 K, (ii) 215 K > T >= 50 K, (iii) 50 K > T >= 40 K, (iv) 40 K > T > 15 K, and (v) T =< 15 K. The corresponding magnetic structures are paramagnetic, commensurate collinear antiferromagnetic (AFM-I), incommensurate AFM (AFM-II), mixed ferromagnetic and AFM (FM+AFM-II), and incommensurate AFM (AFM-II), respectively., 26 pages, 10 figures

The compound Tb 2 C 2 I 2 crystallizes with a layered structure (space group= C2/m ), which has a close-packed arrangement of I–Tb–Tb–I slabs. C 2 units are located within the Tb octahedral voids. Powder magnetic susceptibility measurements suggest two antiferromagnetic ordering transitions below 90 K. From the refinement of neutron powder diffraction patterns, the Tb moments order with a propagation vector k =(0,0,0). The refined Tb moments are 8.0(1) μ B at 10 K, and they are aligned antiferromagnetically in the ac plane.

At the temperatures T N1 ≈2.4 K and T N2 ≈0.7 K, the cubic intermetallic compound Nd 3 Pd 20 Si 6 undergoes second order magnetic phase transitions. Here we report on the magnetic structures obtained from low-temperature neutron diffraction data by using a He dilution refrigerator, and on the crystalline electric field splitting of the Nd 3+ ground state multiplet 4 I 9/2 obtained from inelastic neutron scattering data.

In this work we present a neutron powder diffraction study of the ternary rare-earth phosphides PrFe 4 P 12 and NdFe 4 P 12 . High-resolution measurements of the structural temperature dependence reveal large-amplitude thermal vibrations of the rare-earth ions, consistent with speculations that the ion is weakly bound in an oversized atomic ‘cage’ formed in the skutterudite crystal structure. In addition, low temperature neutron diffraction measurements of RFe 4 P 12 (R=Pr, Nd) were performed. Whereas the proposed long-range antiferromagnetic ordering in PrFe 4 P 12 could not be confirmed, NdFe 4 P 12 orders ferromagnetically below T C =1.94 K with an ordered magnetic Nd 3+ moment of 1.61(7) μ B at 1.5 K.

The oxygen deficient cobaltites LnBaCo2O5 (Ln = Tb, Dy, Ho) exhibit two successive crystallographic transitions at T N ∼340 K and at T CO ∼210 K. Whereas the first transition (P4/mmm to Pmmm) is related to the long-range antiferromagnetic ordering of the Co ions (spin ordering), the second transition (Pmmm to Pmmb) corresponds to the long-range ordering of the Co2+ and Co3+ species (charge ordering) occurring in 1:1 ratio in the structure. The charge ordered (CO) state was directly evidenced by the observation of additional superstructure peaks using neutron and electron diffraction techniques. The CO state was also confirmed indirectly from refinement of high resolution neutron diffraction data as well as from resistivity and DSC measurements. From the refined saturated magnetic moment values only, ∼3.7 and ∼2.7 , the electronic configuration of the Co ions in LnBaCo2O5 remains conjectural. Two pictures, with Co3+ ions either in intermediate spin state ( t 5 2g e 1 g ) or in high spin state ( t 4 2g e 2 g ), describe equally well our experimental data. In both cases, the observed magnetic structure can be explained using the qualitative Goodenough-Kanamori rules for superexchange. Finally, in contrast to the parent Ln = Y compound [Vogt et al. , Phys. Rev. Lett. 84, 2969 (2000)], we do not report any spin transition in LnBaCo2O5 (Ln = Tb, Dy, Ho).

We have performed powder neutron diffraction experiments to examine the magnetic ordering in Ce3Pd20Ge6, which exhibits ferroquadrupolar ordering at TQ1≈1.2 K and antiferromagnetic ordering at TN2 = 0.75 K. In the series of isostructural cubic rare-earth (R) compounds R3Pd20X6 (X = Si, Ge; space group Fmm), it is common that at the Neel temperature TN1 the magnetic moments at the 8c site (simple cubic sublattice) order in an antiferromagnetic sequence with propagation vector k1 = [1,1,1] and at TN2 the magnetic moments at the 4a site (face-centred cubic sublattice) order with a propagation vector k2 = [0,0,1]. In Ce3Pd20Ge6 the Neel temperature TN1 is replaced by TQ1 and at the 8c site a possible ordered cerium moment is found to be reduced to an undetectable small value down to the lowest measured temperature T = 0.05 K. In contrast, at the 4a site the cerium moments order below TN2 with the expected antiferromagnetic structure. The moments align perpendicular to the propagation vector k2 = [0,0,1] with a saturation value µ2(4a) = (1.1±0.1) µB/Ce that is reasonably large for the crystal field ground-state quartet Γ8. Our results provide indirect experimental evidence that only the quadrupolar moments of cerium at the 8c site are involved in the phase transition at TQ1.

The intermetallic compounds R2Pd2In of the light rare earths R = Pr, Nd were investigated by means of powder neutron diffraction in the temperature range from 1.6 K to 15 K. The chemical structure is of Mo2FeB2 type according to the space group P4/mbm. Antiferromagnetic rare-earth ordering of modulated type corresponding to k = [0,0,1/2] and [1/4,1/4,0] was established below the Neel temperatures TN = 5 K and 8 K for R = Pr and Nd, respectively, in contrast to k≈[0.22,0,0] and k = [0,0,0] of the antiferromagnetic and ferromagnetic, nonstoichiometric Ce2Pd2In systems.

For the cubic intermetallic compound Nd 3 Pd 20 Ge 6 (space group Fm 3 m ) magnetic and transport properties are known to be highly sensitive to sample quality. We have performed powder neutron diffraction experiments down to 100 mK to study the magnetic structures of an inhomogeneous Nd 3 Pd 20 Ge 6 sample, which is the only known 3–20–6 system with three successive magnetic phase transitions. The onset of magnetic Nd order at the 8 c site (simple cubic sublattice) is observed in two phase transitions with a dominant commensurate antiferromagnetic component ( k 1 =[1,1,1] below T N1 =1.75 K) and an additional weak incommensurate perturbation ( k 1i =[ τ , τ , τ ], τ =0.79, below T N1i =1.40 K). The Nd moments at the 4 a site (face-centered cubic sublattice) remain disordered down to T N2 =0.58 K and align perpendicular to the propagation vector k 2 =[0,0,1]. The phase transition at T N1i appears because of atomic disorder inside the cubic lattice of the 3–20–6 structure. High-quality Nd 3 Pd 20 Ge 6 samples show only two magnetic phase transitions at T N1 and T N2 .

The magnetic phase diagram of ErGa3, built up from bulk magnetisation data, shows in zero-applied magnetic field two successive transitions at T1=2.6 and T2≅2.8 K, respectively. The magnetic ordering of ErGa3 examined by neutron diffraction, can be derived from the so-called { 1 2 , 1 2 , 0 } structure, i.e. one in which the successive antiparallel (1 1 0) sheets of spins have additionally superimposed on them a sinusoidal modulation parallel to the [1 0 0] axis. The temperature dependence of neutron diffraction diagrams studied on the single crystal, revealed in the range of (2.6–2.78) K an abrupt reorientation of the Er3+ spins from the nearly [1 1 0] direction, towards the [1 0 0] axis. In this way previously observed effect on the polycrystalline sample has been confirmed. This rotation can be attributed to the T1 transition found in the H–T magnetic phase diagram.

The oxygen isotope effect on the magnetic structure and charge ordering in $({\mathrm{La}}_{0.25}{\mathrm{Pr}}_{0.75}{)}_{0.7}{\mathrm{Ca}}_{0.3}{\mathrm{MnO}}_{3}$ was studied by means of neutron powder diffraction. At first it was found that the two investigated samples, one containing the natural mixture of isotopes (99.7% ${}^{16}\mathrm{O}$, metallic at $Tl~100$ K), and the other one enriched by ${}^{18}\mathrm{O}$ in 75% (insulating in the whole temperature range), are identical at room temperature. At the temperature lowering the sample with ${}^{16}\mathrm{O}$ undergoes subsequent antiferromagnetic ${(T}_{\mathrm{AFM}}=150 \mathrm{K})$ and ferromagnetic ${(T}_{\mathrm{FM}}=110 \mathrm{K})$ transitions, while in the sample with ${}^{18}\mathrm{O}$ pure AFM ordering ${(T}_{\mathrm{AFM}}=150 \mathrm{K})$ is found. The temperature dependencies of the neutron diffraction peak intensities associated with charge ordering are also quite different in the samples with ${}^{16}\mathrm{O}$ and ${}^{18}\mathrm{O}$ and correlate with the behavior of the electrical resistivity and the magnetic structure. The temperature behavior of the intensities of the CO and AFM peaks may indicate the presence of phase segregation of the sample with O-16 onto AFM-insulating and FM-metallic phases at low temperature, though no indications of a macroscopic phase segregation were found.

The chemical and magnetic structures of the intermetallic compound were studied by means of bulk magnetic measurements and neutron diffraction. The crystal structure of was confirmed to be isotypic with that of , space group , No 225, with Tb being located at the two crystallographic sites 4a and 8c. The compound undergoes two successive second-order magnetic phase transitions at the Neel temperatures and . Below , the 8c sites order in an antiferromagnetic sequence with a magnetic propagation vector , leaving the 4a sites disordered down to , where additional antiferromagnetic ordering of the 4a sites sets in according to .

A giant isotope effect, wherein the low-temperature metallic state is replaced by an insulator state, was recently observed when 18O was substituted for 16O in (La0.25Pr0.75)0.7Ca0.3MnO3 [N. A. Babushkina, L. M. Belova, O. Yu. Gorbenko et al., Nature (London) 391, 159 (1998)]. In the present work, the temperature evolution of the magnetic structure of two samples of this compound is studied by neutron diffraction. One sample contained a natural mixture of oxygen isotopes, 99.7% 16O, while the other was enriched to 75% with the isotope 18O. It is established that the samples are crystallographically identical at room temperature. As the temperature decreases, the sample with 16O undergoes successive antiferromagnetic (T AFM=5150 K) and ferromagnetic (T FM=110 K) transitions, which lead to the establishment of a noncollinear ferromagnetic structure, while a purely antiferromagnetic (T AFM=150 K) order arises in the sample with 18O. The temperature dependences of the intensities of the diffraction peaks associated with the charge ordering differ substantially in samples with 16O and 18O, and they correlate with the behavior of their electric resistance and magnetic structure.

The rare-earth (R) platinum aluminidesRPtAl crystallize in the orthorhombic TiNiSi-type structure (space group Pnma,Z=4), where magnetic rare-earth atoms form a network of chains parallel to thea-axis and parallel to theb-axis. Magnetic structures and phase transitions ofRPtAl (R=Ce, Pr, Nd) compounds were investigated by systematic measurements of magnetic susceptibility, specific heat, and neutron diffraction on polycrystalline samples. The results reveal a large magnetocrystalline anisotropy and magnetic structures that are dominated by a ferromagnetic component parallel to one of the two chain directions: thea-axis for CePtAl and PrPtAl and theb-axis for NdPtAl. The complex magnetism of CePtAl with three successive magnetic phase transitions (TC=5.9 K,T2=4.3 K,T3=2.5 K) and two coexisting propagation vectors (k1=0 forT≤TC, k2i=[0, 0.46, 0] forT2≤T≤TC, k2=[0, 1/2, 0] forT≤T2) is confirmed to be exceptional amongRPtAl compounds. PrPtAl has a nonmagnetic crystalline-electric field (CEF) ground-state singlet separated by 21 K from the first-excited state CEF singlet and magnetic exchange interactions are strong enough to induce long-range magnetic order (Curie temperatureTC=5.8 K, propagation vector k1=0, magnetic group Pnm′a′, ordered saturation momentm1=1.00(7)μB). NdPtAl is a simple ferromagnet (TC=19.2 K, k1=0, Pn′ma′,m1=2.08(4)μB).

The magnetic properties of the new cubic intermetallic compound have been investigated by neutron scattering and low-temperature specific heat experiments. The results include the refinement of the crystal structure at 10 K (space group , No 225), the observation of three successive magnetic phase transitions (at and ), the determination of the antiferromagnetic structure between and (antiferromagnetically ordered Nd moments on site 8c coexist with disordered Nd moments on site 4a) and the measurement of the crystalline-electric-field (CEF) level scheme in the paramagnetic state. An extrapolation of the CEF parameters obtained for predicts the CEF ground-states to be the triplet in and the quartet in .

Spectroscopic, magnetic, thermal, and transport measurements under pressure are presented which were performed on ${\mathrm{YbCu}}_{5\ensuremath{-}x}{\mathrm{Al}}_{x}$ intermetallics. The substitution of Cu by Al in ${\mathrm{YbCu}}_{5}$ drives the system from an almost divalent behavior of the Yb ion in ${\mathrm{YbCu}}_{5}$ to a trivalent state in ${\mathrm{YbCu}}_{3}{\mathrm{Al}}_{2}$. A compensation between the normal thermal expansion and a valence-driven contraction was found for ${\mathrm{YbCu}}_{4}\mathrm{Al}$. Antiferromagnetic order sets in for $xg1.5$, where an increasing Al content causes both a growing transition temperature and rising saturation moments reaching 2 K and about 2.1${\ensuremath{\mu}}_{\mathrm{B}},$ respectively, for $x=2$. At the critical concentration $(x\ensuremath{\approx}1.5)$ the possibility of a non-Fermi-liquid state is analyzed together with its tuning by pressure.

From magnetic, specific heat, 170Yb Mossbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb2Sn2O7, we show that below the first order transition at 0.15 K all of the Yb3+ ions are long-range magnetically ordered and each has a moment of 1.1?B which lies at ?10° to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [ Phys. Rev. Lett. 108 037202 (2012)] for a pyrochlore lattice of Kramers 1/2 effective spins.

Measurements of the magnetic susceptibility, magnetization, electrical resistivity and neutron diffraction have been performed for the compound Fe(0.5)TiS(2) in which Fe atoms are intercalated between S-Ti-S tri-layers. It has been shown that this compound with a monoclinic crystal structure exhibits an antiferromagnetic (AF) ground state below the Neel temperature T(N) ≈ 140 K. Small deviations from the stoichiometry and some disordering effects caused by the additional low-temperature heat treatment do not affect substantially the AF state in Fe(0.5)TiS(2). According to neutron diffraction data the magnetic structure at 2 K is described by the propagation vector k = (1/4,0,1/4). The Fe magnetic moments with a value of (2.9 ± 0.1) μ(B) are directed at an angle of (78.5 ± 1.8)° to the layers. Application of the magnetic field at T < T(N) induces a metamagnetic phase transition to the ferromagnetic (F) state, which is accompanied by the large magnetoresistance effect (|Δρ/ρ| up to 27%). Below 100 K, the field-induced AF-F transition is found to be irreversible, as evidenced by magnetoresistance and neutron diffraction measurements. The magnetization reversal in the metastable F state is accompanied at low temperatures by substantial hysteresis (ΔH ~ 100 kOe) which is associated with the Ising character of Fe ions.

Magnetization measurements and neutron powder diffraction analyses followed by Rietveld refinement have been carried out in order to investigate the magnetic structures of LaYbO3 and LaHoO3. Both compounds exhibit a negative thermal expansion along the a and b axes. In LaYbO3 Yb3+ spins order at 2.4?K according to a FyGz-type structure, belonging to the Pn?ma? magnetic space group. Conversely, LaHoO3 is paramagnetic down to 1.5?K.

We have developed a theoretical description of energy-transfer between chromophores in various geometries which correspond to actual configurations of polymers in a variety of materials. These include micelles with chromophores in the core or in the corona, such as one might obtain with a diblock copolymer in which chromophores are incorporated in one block, micelles with chromophores at the surface or at the interface between blocks, lamellae, and balls. The distribution of chromophores in this model can be random or described by a variety of functions to investigate situations such as the packing of diblocks at the interface between two homopolymeric phases and the expansion, contraction, or redistribution of micelle coronae which often accompanies changes in solvent characteristics. The calculated quantity, GS(t), is the probability of finding an initially excited chromophore still in the excited state at time t, and is directly related to fluorescence depolarization. The behavior of GS (t) in...