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Showing papers on "Magnetic structure published in 2000"


Journal ArticleDOI
11 Aug 2000-Science
TL;DR: Experimental evidence for a spot of perpendicular magnetization at the center of the vortex is provided by magnetic force microscopy imaging of circular dots of permalloy (Ni(80)Fe(20)) 0.3 to 1 micrometer in diameter and 50 nanometers thick.
Abstract: Spin structures of nanoscale magnetic dots are the subject of increasing scientific effort, as the confinement of spins imposed by the geometrical restrictions makes these structures comparable to some internal characteristic length scales of the magnet. For a vortex (a ferromagnetic dot with a curling magnetic structure), a spot of perpendicular magnetization has been theoretically predicted to exist at the center of the vortex. Experimental evidence for this magnetization spot is provided by magnetic force microscopy imaging of circular dots of permalloy (Ni 80 Fe 20 ) 0.3 to 1 micrometer in diameter and 50 nanometers thick.

1,271 citations


Journal ArticleDOI
09 Jun 2000-Science
TL;DR: These investigations demonstrate a powerful technique for the understanding of complicated magnetic configurations of nanomagnets and thin films engineered from ferromagnetic and antiferromagnetic materials used for magnetoelectronics.
Abstract: A two-dimensional antiferromagnetic structure within a pseudomorphic monolayer film of chemically identical manganese atoms on tungsten(110) was observed with atomic resolution by spin-polarized scanning tunneling microscopy at 16 kelvin. A magnetic superstructure changes the translational symmetry of the surface lattice with respect to the chemical unit cell. It is shown, with the aid of first-principles calculations, that as a result of this, spin-polarized tunneling electrons give rise to an image corresponding to the magnetic superstructure and not to the chemical unit cell. These investigations demonstrate a powerful technique for the understanding of complicated magnetic configurations of nanomagnets and thin films engineered from ferromagnetic and antiferromagnetic materials used for magnetoelectronics.

294 citations


Journal ArticleDOI
TL;DR: In this article, the magnetization distributions in a series of ternary intermetallic compounds based on the composition Co2 YZ where Y is Ti, Mn or Fe and Z a subgroup-B element have been determined from polarized neutron diffraction measurements.
Abstract: The magnetization distributions in a series of ternary intermetallic compounds based on the composition Co2 YZ where Y is Ti, Mn or Fe and Z a subgroup-B element have been determined from polarized neutron diffraction measurements. Comparison of the magnetic structure factors with model calculations shows that the magnetization is associated principally with those atoms which in their elemental state are themselves magnetic. The observed deviations of the magnetic moment distributions from spherical symmetry have been used to deduce which of the 3d sub-bands are active at the Fermi energy. A small moment close to the limits of resolution is observed at some of the Z sites, together with a small delocalized moment which in most cases is negative. The results have been compared with the predictions of band models, which indicate that the Fermi level falls in a broad minimum in the minority-spin density of d states. Although the identity of the bands active at the Fermi surface is in broad agreement with predictions of band-structure calculations (Ishida S, Akazawa S, Kubo Y and Ishida J 1982 J. Phys. F: Met. Phys. 12 1111), the results suggest that there is a finite density of states in the minority-spin d band of manganese. Hence the compounds cannot be classified as half-metallic ferromagnets.

280 citations


Journal ArticleDOI
TL;DR: In this article, a comparison of the results between particle dispersions with different concentrations in polyvinylic alcohol and phosphate-coated particles provides evidence for the interplay between surface anisotropy, intraparticle exchange coupling between surface and core, and interparticle interactions.

277 citations


Journal ArticleDOI
TL;DR: Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination of complex magnetic structures and some earlier conclusions on their magnetic symmetry and properties should be revised.
Abstract: Optical second harmonic spectroscopy is introduced as a powerful supplement for the determination of complex magnetic structures. Experimental efforts are simplified and new degrees of freedom are opened. Thereby, some principal or technical restrictions of neutron or magnetic x-ray diffraction experiments are overcome. High spatial resolution leads to additional information about magnetically ordered matter. As an example, the noncollinear magnetic structure of the hexagonal manganites $R{\mathrm{MnO}}_{3}$ ( $R\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}\mathrm{Sc}$, Y, Ho, Er, Tm, Yb, Lu) is analyzed. The results show that some earlier conclusions on their magnetic symmetry and properties should be revised.

276 citations


Journal ArticleDOI
TL;DR: In this article, the authors review the recent progress in the study of layered magnetic manganites La2−2xSr1+2xMn2O7, which have many unique features of charge transport and magnetism inherent to the quasi-two-dimensional electronic structure.
Abstract: ▪ Abstract We review the recent progress in the study of layered magnetic manganites La2−2xSr1+2xMn2O7, which have many unique features of charge transport and magnetism inherent to the quasi-two-dimensional electronic structure. The system shows a wide variety of magnetic-field-induced phenomena due to the layered crystal and magnetic structure, such as the highly anisotropic ferromagnetic metallic ground state, the colossal magnetoresistance (CMR) effect, and the tunneling-type magnetoresistance (TMR). The charge transport properties, as well as the magnetic ones, strongly depend on the carrier-doping level and the applied pressure, which reflects the variation of the orbital-dependent occupancy of itinerant eg-like electrons. Although the layered manganite is one of a new class of CMR materials, the study of this system may also reveal some of the key issues for understanding the CMR effect in mixed-valent manganese oxide.

168 citations


Journal ArticleDOI
TL;DR: In this paper, the structure of weakly magnetic and strongly magnetic iron sulphide was examined using high-resolution imaging and electron diffraction in a transmission electron microscope (TEM), the measurements of magnetisation versus field and temperature, extended X-ray absorption fine-structure (EXAFS) spectroscopy and neutron diffraction.

158 citations


Journal ArticleDOI
TL;DR: In this article, a straightforward unit cell of symmetry R 3m was obtained for the 300 K structure, with the same symmetry and a similar unit cell also obtained at low temperature, in order to assign non-zero magnetic moments to the iron ions, these being in a collinear, antiferromagnetic alignment This magnetic structure can be described with reference to doubled unit cell axes.
Abstract: The complex perovskite lead iron niobate, Pb(Fe1/2 Nb1/2 )O3 (PFN), has been studied by neutron powder diffraction Following collection of diffraction data at 300 K and at 10 K, structural refinements have been carried out by means of the Rietveld method As expected, a straightforward unit cell of symmetry R 3m was obtained for the 300 K structure, with the same symmetry and a similar unit cell also obtained at low temperature Furthermore, in order to obtain a good agreement with experiment at 10 K, it was necessary to assign non-zero magnetic moments to the iron ions, these being in a collinear, antiferromagnetic alignment This magnetic structure can be described with reference to doubled unit cell axes The factors governing the observed structures of PFN are discussed by comparison with the related system of Pb(Mg1/3 Nb2/3 )O3

125 citations


Journal ArticleDOI
TL;DR: In this article, the orthorhombic NdMnO3 perovskite has been studied on the basis of magnetization and neutron powder diffraction (NPD) data.
Abstract: The orthorhombic NdMnO3 perovskite (space group Pnma ) has been studied on the basis of magnetization and neutron powder diffraction (NPD) data. Magnetization measurements suggest the coexistence of ferromagnetic and antiferromagnetic interactions: magnetization versus magnetic field curves present a remnant magnetization in the ordered region, which is around 1 µB at T = 6 K. The thermal evolution of the magnetic structure has been followed down to 1.5 K from the NPD data. These measurements show that the Mn sub-lattice becomes ordered below T N 78 K with a spin arrangement (C x ,F y ,0), in such a way that a ferromagnetic component appears along the y -direction. The Nd sub-lattice becomes ordered below T 13 K according to a ferromagnetic arrangement with the moments parallel to the y -direction. At T = 1.5 K the magnetic moment values are 3.22(9) µB for Mn atoms and 1.2(2) µB for Nd atoms.

114 citations


Journal ArticleDOI
TL;DR: In this article, the site preference and magnetic properties of Zn-Zr substituted BaM ferrite BaFe12-xZnx/2Zrx/2O19 nanoparticles with x=0-1.6 have been studied using Mossbauer spectra and magnetic measurement.
Abstract: The site preference and magnetic properties of Zn-Zr substituted BaM ferrite BaFe12-xZnx/2Zrx/2O19 nanoparticles with x=0-1.6 have been studied using Mossbauer spectra and magnetic measurement. The results show that the magnetizations and magnetocrystalline anisotropies are closely related to the distributions of Zn-Zr ions on the five sites. The BaFe12-xZnx/2Zrx/2O19 nanoparticles exhibit unusual saturation magnetization, which increase at low substitutions, reach a maximum and then decrease. Massbauer spectra show that the Zn-Zr ions preferentially occupy the 2b and 4f(VI) sites. The preference for the 4f(VI) site is responsible for the anomalous increase in the magnetization at low Zn-Zr substitutions. At x greater than or equal to 1.2 the rapid decrease in the magnetizations is mainly attributed to a noncollinear magnetic structure. In addition, a monotonic decrease in the magnetocrystalline anisotropy with Zn-Zr substitutions has its origin in the preference of the Zn-Zr ions for the 2b and 4f(VI) sites.

107 citations


Journal ArticleDOI
TL;DR: periodic alternations of the intensity of the surface state peak in local tunneling spectra measured above different ferromagnetic terraces separated by monatomic steps confirm the topological antiferromagnetic order of the Cr(001) surface.
Abstract: The magnetic structure of the Cr(001) surface was investigated by spin-polarized scanning tunneling spectroscopy by making use of the spin-polarized surface state located close to the Fermi level. Periodic alternations of the intensity of the surface state peak in local tunneling spectra measured above different ferromagnetic terraces separated by monatomic steps confirm the topological antiferromagnetic order of the Cr(001) surface. Screw dislocations cause topology-induced spin frustration, leading to the formation of domain walls with a width of about 120 nm.

Journal ArticleDOI
TL;DR: In this paper, the crystal structure of 2H perovskite BaMnO3 has been refined from neutron powder diffraction data collected at room temperature and 80 and 1.7 K.
Abstract: The crystal structure of the 2H perovskite BaMnO3 has been refined from neutron powder diffraction data collected at room temperature and 80 and 1.7 K. The structure consists of chains of face-sharing MnO6 octahedra, separated by Ba2+ cations. At room temperature, a = 5.6991(2), c = 4.8148(2) A, space group P63/mmc. At 80 K, a = 9.8467(1), c = 4.8075(1) A, space group P63cm. The structural phase transition introduces a displacement of neighboring chains and reduces the coordination number of Ba2+. Long-range antiferromagnetic ordering is apparent below TN = 59(2) K, with a magnetic moment of 1.31(5) μB per Mn4+ cation at 1.7 K. Neighboring spins within each chain are antiferromagnetically coupled and lie in a plane perpendicular to [001]. The spin directions associated with the chains at (1/3, 2/3, z) and (2/3, 1/3, z) are rotated by ±120° with respect to that of the chain at (0, 0, z).

Journal ArticleDOI
TL;DR: Three-dimensional coordination network solids of MII[C(CN)3]2 (M = V, Cr) composition possess interpenetrating rutile-like network structures, affording a geometrical topology akin to a Kagomé lattice leading to competing spin exchange interactions and spin frustration.
Abstract: Three-dimensional coordination network solids of MII[C(CN)3]2 (M = V, Cr) composition possess interpenetrating rutile-like network structures. Each [C(CN)3]- bonds to three different metal ions in a triangular array, affording a geometrical topology akin to a Kagome lattice leading to competing spin exchange interactions and spin frustration. The crystal and magnetic structure of CrII[C(CN)3] was determined by Rietveld refinement of the powder neutron diffraction data at 2 and 15 K and belongs to the orthorhombic space group Pmna [a = 7.313(1) A, b = 5.453(1) A, c = 10.640(1) A, Z = 2, T = 15 K]. Each CrII has a tetragonally elongated octahedral structure with four Cr-N(1) distances of 2.077(2) A and two significantly longer axial Cr-N(2) distances of 2.452(2) A. Magnetic susceptibility measurements between 1.7 and 300 K reveal strong antiferromagnetic interactions for both V- and Cr[C(CN)3]2 with theta = -67 and -46 K, respectively, from a fit to the Curie-Weiss law. Long-range magnetic ordering does not occur for M = V above 1.7 K, in contrast to M = Cr, which antiferromagnetically orders at low temperature. This is attributed to Jahn-Teller distorted CrII site relieving frustration in one dimension, leading to 2-D Ising antiferromagnetism, as observed by both magnetic susceptibility and specific heat studies. Neutron diffraction experiments at 2 K for Cr[C(CN)3]2 yielded additional Bragg reflections as a result of antiferromagnetic ordering with the moments on the CrII atoms aligned parallel to c and 4.7(1) microB. Fitting of the magnetic order parameter to a power law yielded TN = 6.12(4) K and beta = 0.18(1) consistent with 2-D Ising behavior. A TN of 6.13 K is also observed from the specific heat data.


Journal ArticleDOI
TL;DR: The magnetic phase diagram of La 2-2 x Sr 1+2 x Mn 2 O 7 (0.30 ≤ x ≤ 0.50) was reexamined from the point of view of the crystal structure, particularly the Jahn-Teller (JT) distortion Δ J T of Mn-O 6 octahedra, i.e., the ratio of the averaged apical MnO bond length to the equatorial Mn O bond length as discussed by the authors.
Abstract: The magnetic phase diagram of La 2-2 x Sr 1+2 x Mn 2 O 7 (0.30 ≤ x ≤ 0.50) was reexamined from the point of view of the crystal structure, particularly the Jahn-Teller (JT) distortion Δ J T of Mn-O 6 octahedra, i.e., the ratio of the averaged apical Mn-O bond length to the equatorial Mn-O bond length. We have found that Δ J T decreases with increasing hole concentration x , while the canting angle between neighboring planes continuously increases from 0° (planar ferromagnet: 0.32 ≤ x ≤0.38) to 180° (A-type antiferromagnet (AFM): x =0.48). The dominance of the A-type AFM structure with the decrease of Δ J T can be ascribed to the change in the e g orbital state from d 3 z 2 - r 2 to d x 2 - y 2 .

Journal ArticleDOI
TL;DR: In this article, the magnetic structure of the kagom\'e lattice antiferromagnet potassium jarosite (K jarosite) was examined by means of powder neutron diffraction.
Abstract: We have examined the magnetic structure of the kagom\'e lattice antiferromagnet potassium jarosite (K jarosite: ${\mathrm{KFe}}_{3}{(\mathrm{OH})}_{6}{(\mathrm{S}\mathrm{O}}_{4}{)}_{2})$ by means of powder neutron diffraction. Extremely high degeneracy of the ground states prevents the long-range magnetic ordering at any temperature and the $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ structure is predicted theoretically to be favored rather than the $q=0$ structure at $T=0$ in a kagom\'e lattice Heisenberg antiferromagnet. Nevertheless, K jarosite shows long-range magnetic ordering at 65 K and the ordered magnetic structure was found to be the $q=0$ structure. In addition, although the $q=0$ structure has two degenerated states of ``positive'' and ``negative'' chirality, the observed magnetic structure contains only elemental triangles of positive chirality. We found that a weak single-ion-type anisotropy is crucial for selecting the observed magnetic structure. The long-range magnetic ordering at finite temperature in the jarosite family of compounds can be ascribed to this anisotropy.

Journal ArticleDOI
TL;DR: The 57 Fe spin echo spectra were studied in local magnetic fields of a BiFeO3 ferroelectric antiferromagnet over the temperature range 77-304 K as mentioned in this paper.
Abstract: The 57 Fe spin echo spectra were studied in local magnetic fields of a BiFeO3 ferroelectric antiferromagnet over the temperature range 77–304 K The line shape analysis confirmed the presence of a spatially modulated, incommensurate cycloidal spin structure in BiFeO3 and allowed the actual spin distribution to be reproduced throughout the cycloid length The distribution was found to be essentially anharmonic The modulated structure is stable over the whole temperature range studied The cycloid wave becomes more harmonic with temperature elevation

Journal ArticleDOI
TL;DR: In this paper, structural and magnetic evolutions in manganese ferrite caused by high-energy ball-milling are investigated by X-ray diffraction, magnetization and Mossbauer spectroscopy.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the occurrence of magnetic domains in epitaxially grown MnAs films on GaAs(001) by magnetic force microscopy (MFM) and determined that the direction of the magnetic moments in the domain walls are out-of-plane.
Abstract: We investigate in detail the occurrence of magnetic domains in epitaxially grown MnAs films on GaAs(001) by magnetic force microscopy (MFM). MnAs layers exhibit in their demagnetized state a very complex magnetic domain structure. High resolution MFM images reveal detailed information on the domain wall. Additionally, we imaged magnetic domains in the dependence on the applied magnetic field. This detailed investigation gives new insight into the correlation between film topography and magnetic domain structures. Systematic magnetization measurements in-plane and out-of-plane have shown high anisotropy in our films. The out-of-plane magnetization determined as a function of the applied field reveals that the direction of the magnetic moments in the domain walls are out-of-plane, thus the domain walls are determined as 180° Bloch type.

Journal ArticleDOI
TL;DR: In this paper, high temperature neutron powder diffraction measurements reveal a simultaneous decay of the sublattice magnetisations and the tetragonal distortion of the unit cell dimensions, and a close inspection of the data reveals some systematic ambiguities of the magnetic structure which are analysed in detail.
Abstract: Neutron powder diffraction measurements on η-Mn3N2 and θ-Mn6N5 + x (x = 0.26) revealed the nuclear and magnetic structures of these metallic interstitial compounds. At ambient temperatures the crystal structures of both materials derive from an fcc arrangement of Mn with N occupying octahedral sites. The unit cells are face-centred tetragonal, η-Mn3N2: a = 4.2046(1) A, c = 12.131(1) A ≈ 3 × 4.041 A; θ-Mn6N5.26: a = 4.2193(1) A, c = 4.1287(1) A. Both phases show an antiferromagnetic ordering of the first kind with magnetic moments between 3.3 and 3.8 µB.The data for η-Mn3N2 confirm a previously reported ordered arrangement of N on 2/3 of the octahedral sites and the collinear antiferromagnetic superstructure with the magnetic moments oriented perpendicular to the tetragonal c axis. However, a close inspection of the data reveals some systematic ambiguities of the magnetic structure which are analysed in detail. In θ-Mn6N5 + x (x = 0.26) the N atoms show no long-range occupational order on the octahedral sites. At ambient temperatures the collinear magnetic moments are tilted by 23° relative to the tetragonal c axis. High temperature neutron powder diffraction measurements reveal a simultaneous decay of the sublattice magnetisations and the tetragonal distortion of the cell dimensions. At about 550 K the magnetic moments align parallel to the c axis, and up to the critical temperature of 660 K they decrease continuously to zero. Parallel to this, the tetragonal distortion of the unit cell reduces and finally approaches a face-centred cubic structure.The consequences of the results with respect to the Mn/N phase diagram are discussed.

Journal ArticleDOI
TL;DR: In this article, the authors reported the first observation of chains or columns of paramagnetic fcc phase nucleated in the ferromagnetic bcc phase of carbon steels during the {alpha yields}{gamma} inverse transformation in high magnetic fields.

Journal ArticleDOI
15 May 2000-EPL
TL;DR: In this paper, a zero-field 57Fe NMR spectrum has been observed in the 57Fe-enriched ceramics of BiFeO3 and the analysis of NMR lineshape confirms the existence in this ferroelectric-antiferromagnetic compound of a long-period cycloidal magnetic structure and enables the first reconstruction of the actual spatial spin distribution along the cycloid which is found to be essentially anharmonic.
Abstract: Zero-field 57Fe NMR spectrum has been observed in the 57Fe-enriched ceramics of BiFeO3. The analysis of NMR lineshape confirms the existence in this ferroelectric-antiferromagnetic compound of a long-period cycloidal magnetic structure and enables the first reconstruction of the actual spatial spin distribution along the cycloid which is found to be essentially anharmonic.

Journal ArticleDOI
TL;DR: In this paper, the magnetic structure of the ground state and the nature of the magnetic order of the pressure-induced superconductor was studied under high pressure and the results showed that the magnetism of this compound is basically itinerant despite its high transition temperature.
Abstract: Neutron-diffraction experiments under high pressure have been done to study the magnetic structure of the ground state and the nature of the magnetic order of the pressure-induced superconductor ${\mathrm{CeRh}}_{2}{\mathrm{Si}}_{2}.$ Two models for the magnetic structure of the ground state, namely, a $4\ensuremath{-}\mathbf{q}$ superposed structure and a multidomain structure, have been tested and the former was found to be more realistic, though both of them have some inconsistency with the results of the previous NMR experiment. The pressure dependence of both the transition temperature and magnitude of the ordered magnetic moment indicate that the magnetism of this compound is basically itinerant despite its high transition temperature. Our studies also revealed that, when the pressure is close to the critical magnitude to destroy the antiferromagnetism, the compound can have a ``tiny ordered moment'' which is widely observed in the metallic Kondo-lattice compounds.

Journal ArticleDOI
TL;DR: In this paper, the first field-induced state was obtained on a frustrated triangular lattice antiferromagnet (TLA) CuFeO 2 under an applied magnetic field up to 14.5 T.
Abstract: Neutron diffraction studies on a frustrated triangular lattice antiferromagnet (TLA) CuFeO 2 have been performed under an applied magnetic field up to 14.5 T. The first-field-induced state was foun...

Journal ArticleDOI
TL;DR: In this article, the exchange bias of a partially oxidized thin film of ferromagnetic Co was studied by magnetization measurements and polarized neutron reflectivity (PNR), showing strong effects of training with cycling of the magnetic field.
Abstract: Exchange bias of a partially oxidized thin film of ferromagnetic Co was studied by magnetization measurements and polarized neutron reflectivity (PNR). The magnetization curve shows strong effects of training with cycling of the magnetic field. Reflectivity measurements with the field parallel to the cooling field showed the onset of spin-dependent diffuse scattering—off the specular reflection—after a training cycle. Such scattering, of the Yoneda type, is due to misaligned Co domains possibly close to the Co/CoO interface. Subjecting the field cooled Co/CoO pair to a field perpendicular to the cooling field causes a rotation of the magnetization. The PNR measurements confirmed earlier susceptibility studies by indicating that the rotation of the magnetization is reversible in fields up to 400 Oe. The rotation of the magnetization of Co is uniform across the film thickness.

Journal ArticleDOI
TL;DR: In this paper, the ability of the local density approximation (LDA) in density functional theory to predict the near-edge structure in electron energy-loss spectroscopy in the dipole approximation was investigated.
Abstract: We investigate the ability of the local density approximation (LDA) in density functional theory to predict the near-edge structure in electron energy-loss spectroscopy in the dipole approximation. We include screening of the core hole within the LDA using Slater's transition state theory. We find that anion K-edge threshold energies are systematically overestimated by 4.22±0.44 eV in twelve transition metal carbides and nitrides in the rock-salt (B1) structure. When we apply this `universal' many-electron correction to energy-loss spectra calculated within the transition state approximation to LDA, we find quantitative agreement with experiment to within one or two eV for TiC, TiN and VN. We compare our calculations to a simpler approach using a projected Mulliken density which honours the dipole selection rule, in place of the dipole matrix element itself. We find remarkably close agreement between these two approaches. Finally, we show an anomaly in the near-edge structure in CrN to be due to magnetic structure. In particular, we find that the N K edge in fact probes the magnetic moments and alignments of the Cr sublattice.

Journal ArticleDOI
TL;DR: In this article, the crystal and magnetic structure of double perovskite transition metal oxide, Sr 2 FeMoO 6, which has been grown by the floating-zone method was investigated.
Abstract: We have investigated, crystal and magnetic structure of conducting double perovskite transition metal oxide, Sr 2 FeMoO 6 , which has been grown by the floating-zone method. The resisitvity shows T 2 -dependence in a wide temperature range (50–350 K), perhaps due to magnon scattering. We further have determined the crystal and magnetic structure in the ferrimagnetic state by means of synchrotron radiation X-ray powder measurements as well as neutron powder diffraction experiments.

Journal ArticleDOI
TL;DR: In this paper, the high magnetic field behavior of the triangular lattice antiferromagnet CuFeO_2 was studied using single crystal neutron diffraction measurements in a field of up to 14.5 T and also by magnetisation measurements in up to 12 T.
Abstract: The high magnetic field behaviour of the triangular lattice antiferromagnet CuFeO_2 is studied using single crystal neutron diffraction measurements in a field of up to 14.5 T and also by magnetisation measurements in a field of up to 12 T. At low temperature, two well-defined first order magnetic phase transitions are found in this range of applied magnetic field (H // c): at H_c1=7.6(3)/7.1(3) T and H_c2=13.2(1)/12.7(1) T when ramping the field up/down. In a field above H_c2 the magnetic Bragg peaks show unusual history dependence. In zero field T_N1=14.2(1) K separates a high temperature paramagnetic and an intermediate incommensurate structure, while T_N2=11.1(3) K divides an incommensurate phase from the low-temperature 4-sublattice ground state. The ordering temperature T_N1 is found to be almost field independent, while T_N2 decreases noticeably in applied field. The magnetic phase diagram is discussed in terms of the interactions between an applied magnetic field and the highly frustrated magnetic structure of CuFeO_2

Journal ArticleDOI
TL;DR: In this paper, elastic small q scattering exhibits a modulation with an anisotropic q dependence, which closely reflects the ferromagnetic correlations found for the static clusters, although some characteristics of a canted state are also observed suggesting a weakly inhomogeneous state.
Abstract: Elastic and inelastic neutron-scattering experiments have been performed in a ${\mathrm{La}}_{0.94}{\mathrm{Sr}}_{0.06}{\mathrm{MnO}}_{3}$ untwinned crystal, which exhibits an antiferromagnetic canted magnetic structure with ferromagnetic layers. The elastic small q scattering exhibits a modulation with an anisotropic q dependence. It can be pictured by ferromagnetic inhomogeneities or large magnetic polarons with a platelike shape, the largest size $(\ensuremath{\approx}17 \AA{})$ and largest interpolaron distance $(\ensuremath{\approx}38 \AA{})$ being within the ferromagnetic layers. Comparison with observations performed on Ca-doped samples, which show the growth of the magnetic polarons with doping, suggests that this growth is faster for the Sr than for the Ca substitution. Below the gap of the spin-wave branch typical of the antiferromagnetic layered magnetic structure, an additional spin-wave branch reveals a ferromagnetic and isotropic coupling, already found in Ca-doped samples. Its q-dependent intensity, very anisotropic, closely reflects the ferromagnetic correlations found for the static clusters. All these results agree with a two-phase electronic segregation occurring on a very small scale, although some characteristics of a canted state are also observed suggesting a weakly inhomogeneous state.

Journal ArticleDOI
TL;DR: In this paper, high-resolution and magnetic neutron-diffraction measurements were performed to investigate the crystal and magnetic structures of bilayered FeOCl and polyaniline-intercalated FeOCL.
Abstract: High-resolution and magnetic neutron-diffraction measurements were performed to investigate the crystal and magnetic structures of bilayered FeOCl and polyaniline-intercalated FeOCl. A quasi-two-dimensional crystallographic structure, where charge neutral $({\mathrm{Fe}}_{2}{\mathrm{O}}_{2}{\mathrm{Cl}}_{2}{)}_{n}$ lamellas are weakly linked via Van der Waals interactions, has made FeOCl a good host for accommodating guest molecules. A three-dimensional long-range ordering of the Fe spins in FeOCl develops below 80 K, with a magnetic unit cell 28 times the size of the nuclear one. A spiral magnetic structure was obtained, reflecting the competition between antiferromagnetic superexchange coupling and ferromagnetic direct exchange coupling. Polyaniline intercalation interrupts the magnetic correlations between the neighboring bilayers, rendering a coupled-bilayer quasi-two-dimensional magnetic order for the Fe spins in $({\mathrm{C}}_{6}{\mathrm{D}}_{4}\mathrm{ND}{)}_{0.16}\mathrm{FeOCl}.$ No significant change on the ordering temperature of the Fe spins by the intercalation reaction was observed.