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Showing papers on "Magnetic structure published in 2011"


Journal ArticleDOI
TL;DR: In this paper, a combined experimental and theoretical investigation of the magnetic structure of the honeycomb-lattice magnet Na{}_{2}$IrO${}_{3}$, a candidate for a realization of a gapless spin liquid, is reported.
Abstract: We report a combined experimental and theoretical investigation of the magnetic structure of the honeycomb-lattice magnet Na${}_{2}$IrO${}_{3}$, a candidate for a realization of a gapless spin liquid. Using resonant x-ray magnetic scattering at the Ir ${\mathrm{L}}_{3}$ edge, we find three-dimensional long-range antiferromagnetic order below ${T}_{N}=13.3$ K. From the azimuthal dependence of the magnetic Bragg peak, the ordered moment is determined to be predominantly along the $a$ axis. Combining the experimental data with first-principles calculations, we propose that the most likely spin structure is a zig-zag structure.

231 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of doping on the electric and magnetic properties of BiFeO3 perovskite has been summarized and a review of recent studies on doped biFeOO3 ceramics is presented.
Abstract: BiFeO3, the paradigm of single-phase multiferroic materials, has potential applications in information storage, sensors and actuators This perovskite has a rhombohedral R3c crystallographic structure and shows a spin-modulated cycloidal magnetic structure with a modulation period of ∼62 nm It reveals magnetoelectric coupling at room temperature However, its low remanent magnetization and relatively important leakage current are the main limitations for possible applications In this review we summarize recent studies on doped BiFeO3 Special attention is put on obtaining and sintering bulk BiFeO3 ceramics and the effect of doping on the electric and magnetic properties

229 citations


Journal ArticleDOI
TL;DR: All recently discovered A intercalated iron selenide superconductors share the common crystalline and magnetic structure, which are very different from previous families of Fe-basedsuperconductors, and constitute a distinct new 245 family.
Abstract: Single-crystal neutron diffraction studies on superconductors A(2)Fe(4)Se(5), where A=Rb, Cs, (Tl, Rb), and (Tl, K) (T(c) ∼ 30 K), uncover the same Fe vacancy ordered crystal structure and the same block antiferromagnetic order as in K(2)Fe(4)Se(5). The Fe order-disorder transition occurs at T(S)=500-578 K, and the antiferromagnetic transition at T(N) = 471-559 K with an ordered magnetic moment ∼3.3μ(B)/Fe at 10 K. Thus, all recently discovered A intercalated iron selenide superconductors share the common crystalline and magnetic structure, which are very different from previous families of Fe-based superconductors, and constitute a distinct new 245 family.

178 citations


Journal ArticleDOI
TL;DR: The results show that a low temperature structural phase transition from monoclinic to trigonal is energetically favourable for CrCl(3), and it is observed that the ground state depends critically on the specific approach used.
Abstract: We present results from an electronic structure investigation of the chromium halides CrCl(3), CrBr(3), and CrI(3), as obtained by the linearized augmented plane wave method of density functional theory. Our interest focuses on the chloride. While all three halides display strong ferromagnetic coupling within the halide-Cr-halide triple layers, our emphasis is on differences in the interlayer magnetic coupling. In agreement with experimental results, our calculations indicate ferromagnetic ordering for CrBr(3) as well as CrI(3). The antiferromagnetic state of CrCl(3) can be reproduced by introducing an on-site electron-electron repulsion. However, we observe that the ground state depends critically on the specific approach used. Our results show that a low temperature structural phase transition from monoclinic to trigonal is energetically favourable for CrCl(3).

130 citations


Journal ArticleDOI
TL;DR: In this paper, the authors employ the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an effective equation of motion for the rotational degree of freedom.
Abstract: In chiral magnets without inversion symmetry, the magnetic structure can form a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice, stabilized by spin-orbit interactions in a small range of temperatures and magnetic fields. The twist of the magnetization within this phase gives rise to an efficient coupling of macroscopic magnetic domains to spin currents. We analyze the resulting spin-transfer effects, and, in particular, focus on the current-induced rotation of the magnetic texture by an angle. Such a rotation can arise from macroscopic temperature gradients in the system as has recently been shown experimentally and theoretically. Here we investigate an alternative mechanism, where small distortions of the skyrmion lattice and the transfer of angular momentum to the underlying atomic lattice play the key role. We employ the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an effective equation of motion for the rotational degree of freedom. We discuss the dependence of the rotation angle on the orientation of the applied magnetic field and the distance to the phase transition.

120 citations


Journal ArticleDOI
TL;DR: In this article, powder neutron diffraction and inelastic scattering measurements of frustrated pyrochlore Nd$_2$Ir$_ 2$O$_7, which exhibits a metal-insulator transition at a temperature $T_{\rm MI}$ of 33 K was performed.
Abstract: In this study, we performed powder neutron diffraction and inelastic scattering measurements of frustrated pyrochlore Nd$_2$Ir$_2$O$_7$, which exhibits a metal-insulator transition at a temperature $T_{\rm MI}$ of 33 K The diffraction measurements revealed that the pyrochlore has an antiferromagnetic long-range structure with propagation vector $\vec{q}_{0}$ of (0,0,0) and that it grows with decreasing temperature below 15 K This structure was analyzed to be of the all-in all-out type, consisting of highly anisotropic Nd$^{3+}$ magnetic moments of magnitude $23\pm04$$\mu_{\rm B}$, where $\mu_{\rm B}$ is the Bohr magneton The inelastic scattering measurements revealed that the Kramers ground doublet of Nd$^{3+}$ splits below $T_{\rm MI}$ This suggests the appearance of a static internal magnetic field at the Nd sites, which probably originates from a magnetic order consisting of Ir$^{4+}$ magnetic moments Here, we discuss a magnetic structure model for the Ir order and the relation of the order to the metal-insulator transition in terms of frustration

112 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic structure of individual magnetic monopoles in an artificially frustrated two-dimensional square spin-ice lattice was observed at room temperature using high-resolution aberration-corrected Lorentz transmission electron microscopy.
Abstract: Artificially frustrated spin-ice systems are of considerable interest since they simulate the spin frustration and concomitant rich behavior exhibited by atoms on a crystal lattice in naturally occurring spin-ice systems such as pyrochlores. As a result of the magnetic frustration, these systems can exhibit 'magnetic monopole' type defects, which are an example of an exotic emergent quasiparticle. The local magnetization structure of such monopole defects determines their stability and thus is critical to understanding their behavior. In this paper, we report on the direct observation at room temperature of the nanoscale magnetic structure of individual magnetic monopoles in an artificially frustrated two-dimensional square spin-ice lattice, using high-resolution aberration-corrected Lorentz transmission electron microscopy. By combining the high-resolution microscopy with micromagnetic simulation, we demonstrate how nucleation of defect strings, reminiscent of Dirac strings, connecting monopole defects controls the demagnetization process in these spin-ice lattices.

105 citations


Journal ArticleDOI
TL;DR: In this article, a magnonic crystal was used as an extremely sensitive sensor for detecting magnetic fields, at room temperature and in a normal noisy space, without considering any magnetic shielding.
Abstract: We have experimentally demonstrated that a magnonic crystal—an artificial magnetic structure for controlling propagation of magnetostatic waves—can be used as an extremely sensitive sensor for detecting magnetic fields. Functional characteristics of the sensor were studied at room temperature and in a normal noisy space without considering any magnetic shielding.

99 citations


Journal ArticleDOI
TL;DR: In this article, a model of the magnetic field structure of the helium-strong star HD 37776 was presented, which reconciles for the first time all magnetic observations available for this star.
Abstract: The early-type chemically peculiar stars often show strong magnetic fields on their surfaces. These magnetic topologies are organized on large scales and are believed to be close to an oblique dipole for most of the stars. In a striking exception to this general trend, the helium-strong star HD 37776 shows an extraordinary double-wave rotational modulation of the longitudinal magnetic field measurements, indicating a topologically complex and, possibly, record-strong magnetic field. Here we present a new investigation of the magnetic field structure of HD 37776, using both simple geometrical interpretation of the longitudinal field curve and detailed modeling of the time-resolved circular polarization line profiles with the help of a magnetic Doppler imaging technique. We derive a model of the magnetic field structure of HD 37776, which reconciles for the first time all magnetic observations available for this star. We find that the local surface field strength does not exceed ≈30 kG, while the overall field topology of HD 37776 is dominated by a non-axisymmetric component and represents by far the most complex magnetic field configuration found among early-type stars.

86 citations


Journal ArticleDOI
TL;DR: In this article, the phase diagram of MnSi has been analyzed and its properties have been characterized, forming the basis of current ideas in the physics of strongly correlated chiral electron systems.
Abstract: Manganese silicide (MnSi), a model helimagnetic compound, crystallizes in a B20 structure, whose non-centro-symmetric space group allows a helical (chiral) magnetic structure. The magnetic phase transition temperature of MnSi (29 K at atmospheric pressure) decreases with pressure and approaches zero at about 1.4 GPa. This fact, pointing to possible quantum critical phenomena, has prompted high-pressure studies of MnSi that have revealed a number of fascinating phenomena, in particular, the non-Fermi-liquid behavior of electrical resistivity and the unusual spin state (partial ordering) in the paramagnetic phase. We discuss experimental results characterizing the physical properties and the phase diagram of MnSi and at the same time forming the basis of current ideas in the physics of strongly correlated chiral electron systems.

82 citations


Journal ArticleDOI
TL;DR: In this article, the authors reported new 350 μm polarization observations of the thermal dust emission from the cores surrounding the low-mass, Class 0 young stellar objects L1527, IC348-SMM2, and B335, and used them together with results in the literature to determine whether magnetically regulated corecollapse and star formation models are consistent with the observations.
Abstract: We report new 350 μm polarization observations of the thermal dust emission from the cores surrounding the low-mass, Class 0 young stellar objects L1527, IC348-SMM2, and B335. We have inferred magnetic field directions from these observations and have used them together with results in the literature to determine whether magnetically regulated core-collapse and star formation models are consistent with the observations. These models predict a pseudo-disk with its symmetry axis aligned with the core magnetic field. The models also predict a magnetic field pinch structure on a scale less than or comparable to the infall radii for these sources. In addition, if the core magnetic field aligns (or nearly aligns) the core rotation axis with the magnetic field before core collapse, then the models predict the alignment (or near alignment) of the overall pinch field structure with the bipolar outflows in these sources. We show that if one includes the distorting effects of bipolar outflows on magnetic fields, then in general the observational results for L1527 and IC348-SMM2 are consistent with these magnetically regulated models. We can say the same for B335 only if we assume that the distorting effects of the bipolar outflow on the magnetic fields within the B335 core are much greater than for L1527 and IC348-SMM2. We show that the energy densities of the outflows in all three sources are large enough to distort the magnetic fields predicted by magnetically regulated models.

Journal ArticleDOI
TL;DR: In this article, a strain-controlled tuning of magnetism in transition-metal-atom-decorated graphene has been studied, where the spin-dependent hybridization between TM d and graphene orbital states is responsible for the determination of the local electronic and magnetic structure.
Abstract: We report a strain-controlled tuning of magnetism in transition-metal-atom-decorated graphene. Our first-principles calculations demonstrate that strain can lead to a sudden change in the magnetic configuration of a transition metal (TM) adatom and the local atomic structure in the surrounding graphene layer, which have a dramatic effect on the effective exchange coupling between neighboring TM atoms. A strong spin-dependent hybridization between TM d and graphene � orbital states, derived from the orbital selection rule of the local lattice symmetry, is responsible for the determination of the local electronic and magnetic structure. Our results indicate that the strain can be an effective way to control the magnetism of atomic-scale nanostructures, where the reliable control of their magnetic states is a key step for the future spintronic applications.

Journal ArticleDOI
TL;DR: In this article, a structural and magnetic phase diagram of MnNiGe1-xSnx alloys has been proposed and a remarkable magnetic-field-induced paramagnetic/spiral AFM and FM/AFM magnetostructural transformations are found, and large positive and negative magnetocaloric effects are obtained.
Abstract: The martensitic and magnetic phase transformations in MnNiGe1-xSnx (0 ≤ x ≤ 0.200) alloys were investigated using X-ray diffraction, differential thermal analysis, and magnetization measurements. Results indicate that increasing the Sn substitution in MnNiGe1-xSnx results in 1) a decrease of the martensitic transformation temperature from 460 to 100 K and 2) a conversion of spiral antiferromagnetic (AFM) to antiparallel AFM structure in martensite. Based on these features, a remarkable magnetic-field-induced paramagnetic/spiral AFM and FM/AFM magnetostructural transformations are found, and large positive and negative magnetocaloric effects are obtained. The magnetoresponsive effects of MnNiGe1-xSnx alloys are enhanced by Sn substitution. A structural and magnetic phase diagram of MnNiGe1-xSnx alloys has been proposed.

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties and specific heat of NdFeO3 single crystal were systematically studied in the temperature range from 2 to 300 K, with the gradual transition of the Fe3+ magnetic moment ordering from low temperatures to high temperatures.
Abstract: High quality NdFeO3 single crystal has been grown by the four-mirror image floating zone technique. The magnetic properties and specific heat of NdFeO3 single crystal were systematically studied in the temperature range from 2 to 300 K. A clear spin reorientation behavior is observed in a wide temperature range from 100 to 170 K, with the gradual transition of the Fe3+ magnetic moment ordering from {Gz, Mx}-type ordering at low temperatures to {Gx, Mz}-type ordering at high temperatures. In the temperature range from 170 to 300 K, the value of Mx is not equal to zero. It is assumed a single {Gx, Mz}-type ordering mixed with {Gxz, Mxz}-type orderings. During the spin orientation transition process, the hysteresis loops become narrow with very small coercivity. Based on the specific heat measurement, the Schottky anomaly at very low temperature and the thermal anomalies induced by the spin reorientation were also discussed.

Journal ArticleDOI
TL;DR: In this paper, a variable temperature neutron and synchrotron diffraction study has been performed on the giant magnetoresistant oxypnictides LnMnAsO (Ln = La, Nd).
Abstract: A variable temperature neutron and synchrotron diffraction study have been performed on the giant magnetoresistant oxypnictides LnMnAsO (Ln = La, Nd). The low temperature magnetic structures have been studied and results show a spin reorientation of the Mn2+ spins below TN (Nd) for NdMnAsO. The Mn2+ spins rotate from alignment along c to alignment into the basal plane and the Mn2+ and Nd3+ moments refine to 3.54(4) \mu B and 1.93(4) \mu B respectively at 2 K. In contrast there is no change in magnetic structure with temperature for LaMnAsO. There is no evidence of a structural transition down to 2 K, however discontinuities in the cell volume, Ln-O and Mn-As bond lengths are detected at \sim 150 K for both materials. This temperature coincides with the electronic transition previously reported and suggests a coupling between electronic and lattice degrees of freedom.

Journal ArticleDOI
TL;DR: A microscopic model of the superexchange interaction has been developed on the basis of the crystal structure obtained in this work to account for the behavior of T(N) under high pressure.
Abstract: The temperature-pressure phase diagram for both the crystal and magnetic structures of LaCrO(3) perovskite has been mapped out by in situ neutron-diffraction experiments under pressure. The system offers the opportunity to study the evolution of magnetic order, spin direction, and magnetic moment on crossing the orthorhombic-rhombohedral phase boundary. Moreover, a microscopic model of the superexchange interaction has been developed on the basis of the crystal structure obtained in this work to account for the behavior of T(N) under high pressure.

Journal ArticleDOI
TL;DR: Measurements of the element-specific electronic structure and magnetic response as a function of magnetic field amplitude and orientation for chemically synthesized single Fe nanocubes with 18 nm edge length open new possibilities for a deeper understanding of the collective response of magnetic nanohybrids in multifunctional materials and in nanomagnetic colloidal suspensions used in biomedical and engineering technologies.
Abstract: Correlating the electronic structure and magnetic response with the morphology and crystal structure of the same single ferromagnetic nanoparticle has been up to now an unresolved challenge. Here, we present measurements of the element-specific electronic structure and magnetic response as a function of magnetic field amplitude and orientation for chemically synthesized single Fe nanocubes with 18 nm edge length. Magnetic states and interactions of monomers, dimers, and trimers are analyzed by X-ray photoemission electron microscopy for different particle arrangements. The element-specific electronic structure can be probed and correlated with the changes of magnetic properties. This approach opens new possibilities for a deeper understanding of the collective response of magnetic nanohybrids in multifunctional materials and in nanomagnetic colloidal suspensions used in biomedical and engineering technologies.

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of LiFeSO4F and FeSO4Fs have been characterized using magnetic susceptibility and low-temperature neutron diffraction experiments, and the authors attributed the decreased ordering temperature to a structural change which decreases the strength of the magnetic interactions along the length of the chains and the difference of supersuper-exchange interactions between Fe2+ and Fe3+ ions.
Abstract: Using magnetic susceptibility and low-temperature neutron diffraction experiments we present a thorough characterization of the magnetic properties of LiFeSO4F and FeSO4F. Temperature dependent magnetic susceptibility measurements show a transition to long-range antiferromagnetic order at 100 K in FeSO4F whereas the ordering temperature in LiFeSO4F is 25 K. We attribute the decreased ordering temperature to a structural change which decreases the strength of the magnetic interactions along the length of the chains and to the difference of supersuper-exchange interactions between Fe2+ and Fe3+ ions. Powder neutron diffraction experiments were used to determine the magnetic structures of both compounds, which are discussed in terms of exchange interactions and the anisotropy of Fe2+. The iron magnetic moments are antiparallel within the chains, whereas the coupling between the chains is different in the lithiated compound compared to the delithiated one, resulting in different spin arrangements.

Journal ArticleDOI
TL;DR: The use of neutrons for the determination of magnetic structures has been a hot topic in the last 15 years as discussed by the authors, where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms.
Abstract: In 1949 Shull et al. [1] used for the first time neutrons for the determination of a magnetic structure. Ever since, the need for neutrons for the study of magnetism has increased. Two main reasons can be brought forward to explain this ongoing success: First of all a strong rise in research on functional materials (founding obliges) and secondly the increasing availability of easy to use programmes for the treatment of magnetic neutron diffraction data. The giant magnetoresistance effect, multiferroic materials, magnetoelasticity, magnetic shape memory alloys, magnetocaloric materials, high temperature superconductivity or spin polarized half metals: The last 15 years have seen the event of all these “hot topics” where the knowledge of the magnetism is a prerequisite for understanding the underlying functional mechanisms. Refinement programs like FULLPROF or GSAS and programs for magnetic symmetry analysis like BASIREPS or SARAH make the determination of magnetic structures accessible for non specialists. Following a historical overview on the use of neutron powder diffraction for the determination of magnetic structures, I will try to convince you of the easiness of using magnetic symmetry analysis for the determination of magnetic structures using some recent examples of own research on the rare earth iron borate TbFe3(BO3)4 and the rare earth transition metal telluride Ho6FeTe2.

Journal ArticleDOI
TL;DR: The geometric and magnetic structures of small Pt(n) clusters supported on a graphene layer have been investigated using ab initio density functional calculations including spin-orbit coupling and strong buckling of the graphene layer induced by the Pt-C bonds prevents the formation of a larger number of cluster-support bonds.
Abstract: The geometric and magnetic structures of small Pt n clusters (n = 1 − 5) supported on a graphene layer have been investigated using ab initio density functional calculations including spin-orbit coupling. Pt–Pt interactions were found to be much stronger than the Pt–C interactions promoting the binding to the support. As a consequence, the equilibrium structure of the gas-phase clusters is preserved if they are deposited on graphene. However, the clusters bind to graphene only via at most two Pt–C bonds: A Pt2 dumbbell prefers an upright position, the larger clusters are bound to graphene only via one edge of the planar cluster (Pt3 and Pt5) or via two terminal Pt atoms of a bent Pt4 rhombus. Evidently, the strong buckling of the graphene layer induced by the Pt–C bonds prevents the formation of a larger number of cluster-support bonds. As the local spin and orbital magnetic moments are quenched on the Pt atoms forming Pt–C bonds, the magnetic structure of the supported clusters is much more inhomogeneous as in the gas-phase. This leads to noncollinear magnetic structures and a strongly reduced magnetic anisotropy energy.

Journal ArticleDOI
TL;DR: In this article, the first principles of density functional theory have been applied to the structure of Ni2XGa and Ni2MnGa, and the lattice parameters of both austenitic and martensitic phases have been calculated using the VIENNA AB INITIO software package.
Abstract: The crystallographic, magnetic and electronic structures of the ferromagnetic shape memory alloys Ni2XGa (X=Mn, Fe, and Co), are systematically investigated by means of the first–principles calculations within the framework of density functional theory using the VIENNA AB INITIO SOFTWARE PACKAGE. The lattice parameters of both austenitic and martensitic phases in Ni2MnGa have been calculated. The formation energies of the cubic phase of Ni2XGa are estimated, and show a destabilization tendency if Mn atom is substituted by Fe or Co. From Ni2MnGa to Ni2CoGa, the down spin total density of states (DOS) at Fermi level is gradually increasing, whereas that of the up spin part remains almost unchanged. This is the main origin of the difference of the magnetic moment in these alloys. The partial DOS is dominated by the Ni and Mn 3d states in the bonding region below EF. There are two bond types existing in Ni2XGa: one is between neighboring Ni atoms in Ni2MnGa; the other is between Ni and X atoms in Ni2FeGa and ...

Journal ArticleDOI
TL;DR: In this article, it was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co.
Abstract: Magnetic measurements and neutron powder diffraction experiments on Ni50Mn33Sn17 and Ni45Co5Mn33Sn17 alloys were performed in order to establish the magnetic structures and the effects of Co substitution on the magnetic properties. It was shown that the magnetic coupling between the Mn moments on the 4a and 4b sites changed from being antiferromagnetic to ferromagnetic by substitution of Co. As a result of the change in the magnetic structure due to the Co substitution, the ferromagnetic properties of Ni–Co–Mn–Sn are enhanced. These results have enabled the concentration dependence of the magnetic moment to be quantified.

Journal ArticleDOI
TL;DR: The quaternary full Heusler compound Mn{sub 2-x}Co{sub x}VAl with x = 1 is predicted to be a half-metallic antiferromagnet as mentioned in this paper.
Abstract: The quaternary full Heusler compound Mn{sub 2-x}Co{sub x}VAl with x = 1 is predicted to be a half-metallic antiferromagnet. Thin films of the quaternary compounds with x = 0-2 were prepared by dc and RF magnetron co-sputtering on heated MgO (0 0 1) substrates. The magnetic structure was examined by x-ray magnetic circular dichroism and the chemical disorder was characterized by x-ray diffraction. Ferrimagnetic coupling of V to Mn was observed for Mn{sub 2}VAl (x = 0). For x = 0.5, we also found ferrimagnetic order with V and Co antiparallel to Mn. The observed reduced magnetic moments are interpreted with the help of band structure calculations in the coherent potential approximation. Mn{sub 2}VAl is very sensitive to disorder involving Mn, because nearest-neighbour Mn atoms couple antiferromagnetically. Co{sub 2}VAl has B2 order and has reduced magnetization. In the cases with x {ge} 0.9 conventional ferromagnetism was observed, closely related to the atomic disorder in these compounds.

Journal ArticleDOI
TL;DR: In this paper, the magnetic structure of the itinerant monoarsenide FeAs with the B31 structure is described as a noncollinear spin-density wave arising from a combination of itinerant and localized behavior with spin amplitude along the $b$-axis direction being ($15\ifmmode\pm\pm/else\textpm\fi{}5$)$%$ larger than in the $a$ direction.
Abstract: The nature of the magnetism in the simplest iron arsenide is of fundamental importance in understanding the interplay between localized and itinerant magnetism and superconductivity. We present the magnetic structure of the itinerant monoarsenide FeAs with the B31 structure. Powder neutron diffraction confirms incommensurate modulated magnetism with wave vector $\mathbf{q}=(0.395\ifmmode\pm\else\textpm\fi{}0.001){\mathbf{c}}^{*}$ at 4 K, but can not distinguish between a simple spiral and a collinear spin-density-wave structure. Polarized single-crystal diffraction confirms that the structure is best described as a noncollinear spin-density wave arising from a combination of itinerant and localized behavior with spin amplitude along the $b$-axis direction being ($15\ifmmode\pm\else\textpm\fi{}5$)$%$ larger than in the $a$ direction. Furthermore, the propagation vector is temperature dependent, and the magnetization near the critical point indicates a two-dimensional Heisenberg system. The magnetic structures of closely related systems are discussed and compared to that of FeAs.

Journal ArticleDOI
TL;DR: In this article, the magnetic and magnetoelectric properties of Ba2-xSrxNi2Fe12O22 single crystals over a wide composition range (0,≤ x≤ 1.5) were studied.
Abstract: We studied the magnetic and magnetoelectric properties of Ba2-xSrxNi2Fe12O22 single crystals over a wide composition range (0 ≤ x ≤ 1.5). All the crystals show a ferrimagnetic order at around 660 K. While a Sr-free crystal is simply ferrimagnetic down to the lowest temperature, a transition from the ferrimagnetic into a screw magnetic ordered state was observed at temperatures below 300 K in Sr-substituted crystals. The transition temperature monotonically increases with increasing Sr content, meaning that the screw ordered state is stabilized by the Sr-substitution. By applying a magnetic field perpendicular to the hexagonal c axis, the samples showing the ground-state screw order undergo successive metamagnetic transitions and exhibit magnetically induced ferroelectricity in some of the intermediate magnetic phases. In an intermediate magnetic phase, the largest electric polarization emerges (2 × 102 μC/m2 for x = 1.5 crystal), i.e., magnetoelectric effect. The evolution of the magnetic structures related to the magnetoelectric effect in x = 1.5 crystal was clarified by means of in-field neutron diffraction measurements. Though the magnetoelectric effect in the as-grown crystal was measurable only below ∼100 K due to its low resistivity, a post-annealing drastically enhances the resistivity and allows us to observe the magnetically induced ferroelectricity up to ∼175 K.

Book ChapterDOI
01 Jan 2011
TL;DR: In this article, the magnetic properties of nanoparticles are reviewed with a focus on both theoretical work and how the dynamics can be experimentally observed, including the effects of dipole interactions between ferromagnetic particles and exchange interactions between antiferromagnetic nanoparticles.
Abstract: The magnetic properties of nanoparticles are reviewed. Magnetic domains and single-domain particles are introduced and the magnetic structure and anisotropy of nanoparticles are discussed. The magnetic excitations in magnetic nanoparticles both above the blocking temperature (superparamagnetism) and below the blocking temperature (collective magnetic excitations) are reviewed with a focus on both theoretical work and how the dynamics can be experimentally observed. The effects of dipole interactions between ferromagnetic particles and exchange interactions between antiferromagnetic nanoparticles are discussed. Applications of magnetic nanoparticles and the occurrence of magnetic nanoparticles in nature are reviewed.

Journal ArticleDOI
17 Mar 2011-Nature
TL;DR: The results provide compelling evidence that the hour-glass spectrum in the copper oxide superconductors arises from fluctuating stripes, which means that its magnetic dynamics can conclusively be ascribed to stripes.
Abstract: Neutron scattering measurements of spin fluctuations in hole-doped high-Tc copper oxides have revealed an unusual 'hour-glass' feature in the momentum-resolved magnetic spectrum. There is no widely accepted explanation for this feature. One possibility is that it derives from a pattern of alternating spin and charge stripes. Many copper oxides without stripe order, however, also exhibit an hour-glass spectrum. This paper reports the observation of an hour-glass magnetic spectrum in a hole-doped antiferromagnet from outside the family of superconducting copper oxides. The system has stripe correlations and is an insulator, which means its magnetic dynamics can conclusively be ascribed to stripes. The results provide compelling evidence that the hour-glass spectrum in the copper-oxide superconductors arises from fluctuating stripes.

Journal ArticleDOI
TL;DR: In this paper, a terahertz spectroscopic study of magnetic excitations in ferroelectric antiferromagnet BiFeO3 is presented, where the authors interpret the observed spectrum of longwavelength magnetic resonance modes in terms of the normal modes of the material's cycloidal Antiferromagnetic structure and find that the modulated Dzyaloshinski-Moriya interaction leads to a splitting of the out-ofplane resonance modes.
Abstract: We present a terahertz spectroscopic study of magnetic excitations in ferroelectric antiferromagnet BiFeO3 We interpret the observed spectrum of long-wavelength magnetic resonance modes in terms of the normal modes of the material's cycloidal antiferromagnetic structure We find that the modulated Dzyaloshinski-Moriya interaction leads to a splitting of the out-of-plane resonance modes We also assign one of the observed absorption lines to an electromagnon excitation that results from the magnetoelectric coupling between the ferroelectric polarization and the cycloidal magnetic structure of BiFeO3

Journal ArticleDOI
TL;DR: In this article, detailed neutron scattering measurements of the magnetic excitation spectrum of CuCrO$ in the ordered state below 24.2$ K are presented, and the spectra are analyzed using a model Hamiltonian which includes intralayer exchange up to the next-next-nearest neighbor and interlayer exchange.
Abstract: In this paper detailed neutron scattering measurements of the magnetic excitation spectrum of CuCrO${}_{2}$ in the ordered state below ${T}_{\mathrm{N}1}=24.2$ K are presented. The spectra are analyzed using a model Hamiltonian which includes intralayer exchange up to the next-next-nearest neighbor and interlayer exchange. We obtain a definite parameter set and show that exchange interaction terms beyond the next-nearest neighbor are important to describe the inelastic excitation spectrum. The magnetic ground state structure generated with our parameter set is in agreement with the structure proposed for CuCrO${}_{2}$ from the results of single crystal diffraction experiments previously published. We argue that the role of the interlayer exchange is crucial to understand the incommensurability of the magnetic structure as well as the spin-charge coupling mechanism.

Journal ArticleDOI
TL;DR: It is shown that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures by using the resonant x-ray excitation process and coherent x-rays scattering.
Abstract: We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co L{sub 3} edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.