Local magnetostructural changes and dynamical spin fluctuations in doubly diluted spinel TixMn1-x(FeyCo1-y)(2)O-4 has been reported by means of neutron diffraction and magnetization studies. Two distinct sets of compositions (i) x(Ti) = 0.20 and y(Fe) = 0.18; (ii) x(Ti) = 0.40 and y(Fe) = 0.435 have been considered for this study. The first compound of equivalent stoichiometry Ti0.20Mn0.80Fe0.36Co1.64O4 exhibits enhanced tetragonal distortion across the ferrimagnetic transition temperature T-C = 258 K in comparison to the end compound MnCo2O4 (T-C similar to 180 K) with a characteristic ratio c(t)/root 2a(t) of 0.99795(8) demonstrating robust lattice-spin-orbital coupling. However, in the second case Ti0.40Mn0.60Fe0.87Co1.13O4 with higher B-site compositions, the presence of Jahn-Teller ions with distinct behavior appears to counterbalance the strong tetragonal distortion thereby ceasing the lattice-spin-orbital coupling. Both the investigated systems show the coexistence of noncollinear antiferromagnetic and ferrimagnetic components in cubic and tetragonal settings. On the other hand, the dynamical ac-susceptibility, chi(ac)(T) reveals a cluster spin-glass state with Gabay-Toulouse (GT) like mixed phases behaviour below T-C. Such dispersive behaviour appears to be sensitive to the level of octahedral substitution. Further, the field dependence of chi(ac)(T) follows the weak anisotropic GT-line behaviour with crossover exponent Phi lies in the range 1.38-1.52 on the H-T plane which is in contrast to the B-site Ti substituted MnCo2O4 spinel that appears to follow irreversible non-mean-field AT-line behaviour (Phi similar to 3 + delta). Finally, the Arrott plots analysis indicates the presence of a pseudo first-order like transition (T < 20 K) which is in consonance with and zero crossover of the magnetic entropy change within the frozen spin-glass regime.

The magnetic order and phase transitions in the normal spinel system Ni1-xCuxCr2O4 are studied by powder-neutron and x-ray diffraction, as well as by magnetization measurements to get a complete magnetic phase diagram. For chromites with x(Cu) > 0.5 a canted antiferromagnetic phase of Cr appears first, followed by the onset of ferromagnetism in the Cu sublattice at lower temperature forming a ferrimagnetic lattice. Conversely, with x(Cu) < 0.5 the ferrimagnetic order between the Cr and Cu spins occurs at the higher ordering temperature followed by the onset of antiferromagnetic order in the Cr sublattice. Apart from the crossing of the two boundary lines of the transition temperatures at x(Cu) = 0.50 a compensation point of the ferrimagnetic moments is determined at x(Cu) = 0.60, where the spontaneous magnetization has almost completely vanished. Most remarkable is the antiferromagnetic Cr ordering on the orthorhombic distorted pyrochlore lattice for samples in the x(Cu) range from 0 to 0.12 due to the large variety of coexisting magnetic phases. In the magnetic ground state of NiCr2O4 two commensurate antiferromagnetic structures with the propagation vectors k(AF) = (0,0,1) and (<1/2>,1/2,1/2) coexist. With increasing Cu content from x(Cu) = 0 to 0.09 these phases undergo a transition to another commensurate structure with k = 0 via two coexisting incommensurate magnetic phases with the vectors k(IC1) = (0,0,k(z)) and k(IC2) = (0,k(y),k(z)). The different magnetic phases are discussed qualitatively based on the lattice dimensions depending on the concentration ratio of two Jahn-Teller ions at the tetrahedral A site, where Ni2+ causes elongated and Cu2+ compressed tetragonal lattice distortions. Further, magnetoelasticity studies on selected samples indicate that the magnetically induced lattice strains follow the symmetry of the underlying Jahn-Teller distorted lattices.

Non-graphitic carbons (NGCs), such as glass-like carbons, pitch cokes, and activated carbon consist of small graphene layer building stacks arranged in a turbostratic order. Both structure features, including the single graphene sheets as well as the stacks, possess structural disorder, which can be determined using wide-angle X-ray or neutron scattering (WAXS/WANS). Even if WANS data of NGCs have already been extensively reported and evaluated in different studies, there are still open questions with regard to their validation with WAXS, which is usually used for routine characterization. In particular, using WAXS for the damping of the atomic form factor and the limited measured range prevent the analysis of higher-ordered reflections, which are crucial for determining the stack/layer size (La, Lc) and disorder (σ1, σ3) based on the reflection widths. Therefore, in this study, powder WANS was performed on three types of carbon materials (glass-like carbon made out of a phenol-formaldehyde resin (PF-R), a mesophase pitch (MP), and a low softening-point pitch (LSPP)) using a beamline at ILL in Grenoble, providing a small wavelength and thus generating WANS data covering a large range of scattering vectors (0.052 Å−1 < s < 3.76 Å−1). Merging these WANS data with WANS data from previous studies, possessing high resolution in the small s range, on the same materials allowed us to determine both the interlayer and the interlayer structure as accurately as possible. As a main conclusion, we found that the structural disorder of the graphene layers themselves was significantly smaller than previously assumed.

We report a systematic study on the structural and magnetic properties of off-stoichiometric polycrystalline bulk spinels Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4 using neutron and x-ray diffraction, ferromagnetic resonance, and magnetic measurements. Both compounds show a weak tetragonal distortion with c/a < 1, where the crystal structure could be refined in the tetragonal space group I4(1)/amd. Both Co2+ and Cu2+ ions are located at the tetrahedral A site, and Mn3+ and Co3+ at the octahedral B site. Ferrimagnetic (FI) ordering of Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4 sets in below 184 and 164 K, respectively. Magnetic structure analysis revealed that the ferrimagnetically coupled A(2+)- and B3+-site moments are aligned parallel to the tetragonal c axis. Additionally, a noncollinear antiferromagnetic order appears in the ab plane, where the moments point along [110] and [1 (1) over bar0] . The net magnetic moment [2 mu(FI)(Mn-B/Co-B) - mu(FI)(Co-A)] of Mn1.15Co1.85O4 obtained from neutron data varies between 0.88-1.08 p,B which is in good agreement with M = 0.89-1.13 p,B as determined from magnetization measurements. However, for the Cu-containing compound a larger discrepancy in the magnetic moment was observed between the neutron data (1.89-1.92 mu B ) and low-temperature (T = 1.9 K) field-dependent (H = 90 kOe) magnetization data (0.97-1.21 mu B ). From the three-sublattice model we obtained canting angles 28 degrees and 25 degrees for Mn1.15Co1.85O4 and Mn1.17Co1.60Cu0.23O4, respectively. Both the bulk systems exhibit high magnetocrystalline anisotropy (K-u similar to 9 x 10(5) and 7.5 x 10(5) erg/cm(3)) and a field-induced transition (H-D) across 4.0 kOe due to the domain reorientation. Temperature (1.9-350 K) and field (+/- 90 kOe) dependence of magnetization data confirms the high-spin (S = 3/2 and S = 2) ground-state configuration for both the divalent Co and trivalent Mn.

We present a combined experimental and theoretical study of the mineral atacamite Cu_{2}Cl(OH)_{3}. Density-functional theory yields a Hamiltonian describing anisotropic sawtooth chains with weak 3D connections. Experimentally, we fully characterize the antiferromagnetically ordered state. Magnetic order shows a complex evolution with the magnetic field, while, starting at 31.5 T, we observe a plateaulike magnetization at about M_{sat}/2. Based on complementary theoretical approaches, we show that the latter is unrelated to the known magnetization plateau of a sawtooth chain. Instead, we provide evidence that the magnetization process in atacamite is a field-driven canting of a 3D network of weakly coupled sawtooth chains that form giant moments.

Magnetic frustration in metals is scarce and hard to pinpoint, but exciting due to the possibility of the emergence of fascinating novel phases. The cubic intermetallic compound HoInCu$_4$ with all holmium atoms on an fcc lattice, exhibits partial magnetic frustration, yielding a ground state where half of the Ho moments remain without long-range order, as evidenced by our neutron scattering experiments. The substitution of In with Cd results in HoCdCu$_4$ in a full breakdown of magnetic frustration. Consequently we found a fully ordered magnetic structure in our neutron diffraction experiments. These findings are in agreement with the local energy scales and crystal electric field excitations, which we determined from specific heat and inelastic neutron scattering data. The electronic density of states for the itinerant bands acts as tuning parameter for the ratio between nearest-neighbor and next-nearest-neighbor interactions and thus for magnetic frustration.

A systematic study using neutron diffraction and magnetic susceptibility is reported on Mn substituted ferrimagnetic inverse spinel Ti1-x Mn x Co2O4 in the temperature interval 1.6 K [Formula: see text] T [Formula: see text] 300 K. Our neutron diffraction study reveals cooperative distortions of the TO6 octahedra in the Ti1-x Mn x Co2O4 system for all the Jahn-Teller active ions T  =  Mn3+ , Ti3+ and Co3+ , having the electronic configurations 3d 1, 3d 4 and 3d 6, respectively which are confirmed by the x-ray photoelectron spectroscopy. Two specific compositions (x  =  0.2 and 0.4) have been chosen in this study because these two systems show unique features such as; (i) noncollinear Yafet-Kittel type magnetic ordering, and (ii) weak tetragonal distortion with c/a  <  1, in which the apical bond length d c (T B -O) is longer than the equatorial bond length d ab (T B -O) due to the splitting of the e g level of Mn3+ ions into [Formula: see text] and [Formula: see text]. For the composition x  =  0.4, the distortion in the T B O6 octahedra is stronger as compared to x  =  0.2 because of the higher content of trivalent Mn. Ferrimagnetic ordering in Ti0.6Mn0.4Co2O4 and Ti0.8Mn0.2Co2O4 sets in at 110.3 and 78.2 K, respectively due to the presence of unequal magnetic moments of cations, where Ti3+ , Mn3+ , and Co3+ occupy the octahedral, whereas, Co2+ sits in the tetrahedral site. For both compounds an additional weak antiferromagnetic component could be observed lying perpendicular to the ferrimagnetic component. The analysis of static and dynamic magnetic susceptibilities combined with the heat-capacity data reveals a magnetic compensation phenomenon (MCP) at T COMP  =  25.4 K in Ti0.8Mn0.2Co2O4 and a reentrant spin-glass behaviour in Ti0.6Mn0.4Co2O4 with a freezing temperature of  ∼110.1 K. The MCP in this compound is characterized by sign reversal of magnetization and bipolar exchange bias effect below T COMP with its magnitude depending on the direction of external magnetic field and the cooling protocol.

In ferrimagnetic spinels AB(2)O(4) the magnetic structure is strongly influenced by lattice distortions, geometric frustration and the electronic properties of the cations at the A and B sites. Here, we report a comprehensive study on the temperature dependence of the magnetic structure of CuCr2O4 and Cu0.9Ni0.1Cr2O4 using neutron diffraction. CuCr2O4 undergoes a first continuous magnetic transition around 155 K into a canted long-range spin order on the Cr sublattice established by an antiferromagnetic and a ferromagnetic mode. Below 130 K a second transition occurs into a ferromagnetic order on the Cu sublattice resulting in a ferrimagnetic spin arrangement. Correlations between the appearance of magnetic modes and changes in the lattice geometry at different temperatures are discussed giving insight to magnetoelastic coupling. The occurrence of a ferromagnetic Cr mode above 130 K questions the common interpretation that a strong antiferromagnetic coupling between A and B spins in ferrimagnetic AB(2)O(4) spinels is responsible for spin canting. From our neutron diffraction measurements of Cu1-xNixCr2O4 we identify a spin reorientation for the ferromagnetic modes with a nickel content between x = 0 and 0.1.

Anisotropy of bulk magnetic properties and magnetic structure studies of a Tb2Pd2In single crystal by means of bulk magnetization methods and neutron diffraction techniques confirmed the antiferromagnetic order below the Neel temperature 29.5 K. The collinear magnetic structure of Tb magnetic moments aligned along the tetragonal c-axis is characterized by a propagation vector k = (1/4, 1/4, 1/2), yielding an equal-moment structure with alternating coupling between nearest as well as next-nearest Tb neighbors within the basal plane and antiferromagnetic coupling between the c-axis neighbors. In the context of magnetism of R2T2X compounds, where R stands for rare-earth or actinide element, such collinear structure with long-wavelength periodicity represents a new type of magnetic structure.

The distinctive character of water ice results from the partially disordered combination of covalent and hydrogen bonds in the network of hydrogen and oxygen atoms. The nontrivial hydrogen correlations we report in diffuse neutron scattering are analytically fit via a description of this state as a topological system exhibiting an emergent gauge field. This allows for the density of correlation-terminating point defects to be determined as one defect per 500 oxygen sites at 30 K. Application of an analytical model of ice paves the way towards a detailed understanding of this ubiquitous solid.

We report on a detailed neutron diffraction and H-1-NMR study on the frustrated spin-1/2 chain material linarite, PbCuSO4(OH)(2), where competing ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor interactions lead to frustration. From the magnetic Bragg peak intensity studied down to 60 mK, the magnetic moment per Cu atom is obtained within the whole magnetic phase diagram for H vertical bar vertical bar b axis. Further, we establish the detailed configurations of the shift of the SDW propagation vector in phase V with field and temperature. Finally, combining our neutron diffraction results with those from a low-temperature/high-field NMR study, we find an even more complex phase diagram close to the quasisaturation field suggesting that bound two-magnon excitations are the lowest energy excitations close to and in the quasisaturation regime. Qualitatively and semiquantitatively, we relate such behavior to XYZ exchange anisotropy and contributions from the Dzyaloshinsky-Moriya interaction to affect the magnetic properties of linarite.

Oliver Stockert, ∗ Jens-Uwe Hoffmann, Martin Mühlbauer, Anatoliy Senyshyn, Michael M. Koza, Alexander A. Tsirlin, F. Maximilian Wolf, Sebastian Bachus, Philipp Gegenwart, Roman Movshovich, Svilen Bobev, and Veronika Fritsch † Max-Planck-Institut für Chemische Physik fester Stoffe, 01187 Dresden, Germany Helmholtz-Zentrum Berlin für Materialien und Energie, 14109 Berlin, Germany Heinz Maier-Leibnitz Zentrum, 85747 Garching, Germany Institut Laue-Langevin, 38042 Grenoble, France Experimental Physics VI, Center for Electronic Correlations and Magnetism, Institute of Physics, University of Augsburg, 86135 Augsburg, Germany MPA-CMMS, Los Alamos National Laboratory, Los Alamos, New Mexico 87545, USA Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA (Dated: July 24, 2019)

Non-graphitic carbons (NGCs) represent the most abundant class of sp2-hybridized carbon, materials (coal char coal, activated carbon, etc.). These carbons consist of small graphene layer stacks possessing significant structural disorder in both the single graphene sheets and the stacking. In this study an advanced evaluation approach for wide-angle neutron scattering (WANS) was developed, based on the method introduced by Ruland and Smarsly in 2002. In particular, we elucidated if and how the enhanced WANS data quality and larger values of the modulus of the scattering vector s-range affect the accuracy and the values of the size and disorder parameters—being fitting parameters by themselves—in comparison to wide-angle X-ray scattering (WAXS), which is usually performed by laboratory equipment. We find a reasonable agreement for the parameters La and Lc, that is, the lateral dimension and stack height, within the error bars, whereas for the disorder parameters different results for WAXS and WANS were found, the origin of which is discussed. Thus, this study addresses the general issue of how reliably microstructural parameters can be determined from WAXS/WANS by fitting simulated WAXS and WANS curves, which are quality-impaired by added Gaussian noise at different levels and cut-off at different s-values. From this analysis, we estimated the minimal data quality required for a reliable NGC microstructural analysis based on WAXS/WANS. As an important finding, these simulations show that typical, standard WAXS laboratory setups are sufficient to provide reliable values for the most relevant structural parameters. Furthermore, pair-distribution function (PDF) analyses were performed on WAXS data obtained from a synchrotron facility. Comparing PDF and WAXS/WANS fitting analysis suggests the presence of small highly ordered oligoaromatic domains embedded in the larger graphene sheets, questioning the classical view on the NGC microstructure.

L. Heinze,1 G. Bastien,2 B. Ryll,3 J.-U. Hoffmann,3 M. Reehuis,3 B. Ouladdiaf,4 F. Bert,5 E. Kermarrec,5 P. Mendels,5 S. Nishimoto,2,6 S.-L. Drechsler,2 U. K. Rößler,2 H. Rosner,7 B. Büchner,2,8 A. J. Studer,9 K. C. Rule,9 S. Süllow,1 and A. U. B. Wolter2 1Institut für Physik der Kondensierten Materie, TU Braunschweig, D-38106 Braunschweig, Germany 2Leibniz-Institut für Festkörperund Werkstoffforschung IFW Dresden, D-01171 Dresden, Germany 3Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany 4Institute Laue-Langevin, F-38042 Grenoble Cedex, France 5Laboratoire de Physique des Solides, CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay Cedex, France 6Institut für Theoretische Physik, Technische Universität Dresden, D-01068 Dresden, Germany 7Max-Planck-Institut für Chemische Physik fester Stoffe, D-01068 Dresden, Germany 8Institut für Festkörperund Materialphysik, Technische Universität Dresden, D-01062 Dresden, Germany 9Australian Centre for Neutron Scattering, ANSTO, Kirrawee DC, New South Wales 2234, Australia

The magnetic order/disorder of the Cr-moments in the antiferromagnetic (AF) state of the ferrimagnet NiCr2O4 is reinvestigated by neutron powder diffraction to clarify the observation of reduced Cr moments located on a pyrochlore like lattice [M. Reehuis et al., Phys. Rev. B 91, 024407 (2015)]. The change of the spin structure in the slightly Cu-doped chromite Ni0.98Cu0.02Cr2O4 has been studied, where orthorhombic lattice distortions are stronger. For both chromites we observe at 2 K two magnetic phases: one with two propagation vectors k = (0,0,1) and (0,0,kz), and a second one with k = (1⁄2,1⁄2,1⁄2). The latter phase disappears at 21 K for NiCr2O4 and at 24 K for Ni0.98Cu0.02Cr2O4. Data analysis shows that the two wave vectors can be assigned to two magnetic phases residing on two disparate Cr sublattices. These are identified by different chain directions of strongly bonded spin pairs along diagonals in the pseudo-tetragonal a1a2 plane. The less distorted NiCr2O4 shows the same subdivision of the lattice still with a saturated Cr moment for the (0,0,1)/(0,0,kz) phase, however, with a strongly reduced moment for the (1⁄2,1⁄2,1⁄2) phase, whereas an almost saturated moment shows up in the Cu-doped chromite. The reduced moment in NiCr2O4 indicates disorder on one Cr sublattice down to low temperature due to stronger frustration on the less distorted tetragonal pyrochlore lattice. Magnetoelastic effects and further neighbor spin interactions are mainly considered in the discussion of the observed peculiar ordering processes. Notable is the transition temperature of the (1⁄2,1⁄2,1⁄2) phase of NiCr2O4 around 21 K, where new anomalies for the specific heat and for the magnetodielectric behavior have recently been reported [T. D. Sparks et al., Phys. Rev. B 89, 024405 (2014)].

We present a single-crystal diffuse neutron scattering study on the quantum spin ice candidate Nd2Zr2O7 pyrochlore in magnetic fields along the (110) direction. Two-dimensional scattering sheets perpendicular to the (1 (1) over bar0) direction were observed, evidencing field-induced one-dimensional correlations and disorder. The pyrochlore lattice is completely separated into orthogonal sets of chains, which is in strong contrast to classical spin ice and surprising for an "all-in-all-out" (AIAO) ordered magnet with a non-Ising Hamiltonian. Our mean-field and Monte Carlo simulations reveal that the (110) field induces a transition from the AIAO order to a "two-in-two-out" disordered state with interactions between the two sets of chains canceled out, resulting in disorder and quantum spin-1/2 XYZ chains.

The flat-cone diffractometer E2 at the research reactor BER II is a thermal neutron single-crystal diffractometer for 3D reciprocal space mapping by using four delay-line area detectors (300 × 300 mm2). Alternatively it is suitable for powder measurements with medium resolution and broad 2-theta scattering range.

We present susceptibility measurements on the natural mineral atacamite, Cu2Cl(OH)(3), for the first time along the three crystallographic axes. Further, we have carried out an elastic neutron diffraction experiment which shows that the symmetry of the magnetic ground state of atacamite is described by a propagation vector q=(1/2 0 1/2).