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Showing papers on "Magnetic structure published in 2017"


Journal ArticleDOI
20 Jul 2017-Nature
TL;DR: This work image the three-dimensional magnetic structure in the vicinity of the Bloch points, which until now has been accessible only through micromagnetic simulations, and identifies two possible magnetization configurations: a circulating magnetization structure and a twisted state that appears to correspond to an ‘anti-Bloch point’.
Abstract: Techniques exist for imaging the magnetization patterns of magnetic thin films and at the surfaces of magnets, but here hard-X-ray tomography is used to image the three-dimensional magnetic structure within a micrometre-sized magnet in the vicinity of Bloch points. Techniques have long existed for imaging the two-dimensional magnetization patterns of thin-film magnets, but the three-dimensional complexities of magnetization structure within the body of a magnet is not so amenable to direct investigation. Claire Donnelly et al. have made substantial progress in lifting this veil by harnessing hard-X-ray tomography to determine the inner magnetic structure of micrometre-sized magnets. The properties of current X-ray sources limit the spatial resolution to about 100 nanometres, but it is anticipated that future instrumental developments could greatly improve on this. In soft ferromagnetic materials, the smoothly varying magnetization leads to the formation of fundamental patterns such as domains, vortices and domain walls1. These have been studied extensively in thin films of thicknesses up to around 200 nanometres, in which the magnetization is accessible with current transmission imaging methods that make use of electrons or soft X-rays. In thicker samples, however, in which the magnetization structure varies throughout the thickness and is intrinsically three dimensional, determining the complex magnetic structure directly still represents a challenge1,3. We have developed hard-X-ray vector nanotomography with which to determine the three-dimensional magnetic configuration at the nanoscale within micrometre-sized samples. We imaged the structure of the magnetization within a soft magnetic pillar of diameter 5 micrometres with a spatial resolution of 100 nanometres and, within the bulk, observed a complex magnetic configuration that consists of vortices and antivortices that form cross-tie walls and vortex walls along intersecting planes. At the intersections of these structures, magnetic singularities—Bloch points—occur. These were predicted more than fifty years ago4 but have so far not been directly observed. Here we image the three-dimensional magnetic structure in the vicinity of the Bloch points, which until now has been accessible only through micromagnetic simulations, and identify two possible magnetization configurations: a circulating magnetization structure5 and a twisted state that appears to correspond to an ‘anti-Bloch point’. Our imaging method enables the nanoscale study of topological magnetic structures6 in systems with sizes of the order of tens of micrometres. Knowledge of internal nanomagnetic textures is critical for understanding macroscopic magnetic properties and for designing bulk magnets for technological applications7.

235 citations


Journal ArticleDOI
Abstract: We present experimental data showing that the equiatomic CrMnFeCoNi high-entropy alloy undergoes two magnetic transformations at temperatures below 100 K while maintaining its fcc structure down to 3 K. The first transition, paramagnetic to spin glass, was detected at 93 K and the second transition of the ferromagnetic type occurred at 38 K. Field-assisted cooling below 38 K resulted in a systematic vertical shift of the hysteresis curves. Strength and direction of the associated magnetization bias was proportional to the strength and direction of the cooling field and shows a linear dependence with a slope of $0.006\ifmmode\pm\else\textpm\fi{}0.001 \mathrm{emu}\mathrm{T}$. The local magnetic moments of individual atoms in the CrMnFeCoNi quinary fcc random solid solution were investigated by ab initio (electronic density functional theory) calculations. Results of the numerical analysis suggest that, irrespective of the initial configuration of local magnetic moments, the magnetic moments associated with Cr atoms align antiferromagnetically with respect to a cumulative magnetic moment of their first coordination shell. The ab initio calculations further showed that the magnetic moments of Fe and Mn atoms remain strong (between 1.5 and $2\phantom{\rule{0.28em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$), while the local moments of Ni atoms effectively vanish. These results indicate that interactions of Mn- and/or Fe-located moments with the surrounding magnetic structure account for the observed macroscopic magnetization bias.

117 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of light diamagnetic doping on the nature of indirect exchange interactions with temperature increase has been discussed, and the light-diamagnetic doping mechanism and magnetic structure model are proposed.

100 citations


Journal ArticleDOI
TL;DR: A commensurate non-collinear magnetic structure in CdMn 7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12 is observed, however, the Commensurate propagation vector prevents the appearance of a helical magnetic structure.
Abstract: We report on the magnetic structure of CdMn7O12 determined by powder neutron diffraction. We were able to measure the magnetic structure of this Cd containing and highly neutron absorbing material by optimizing the sample geometry and by blending the CdMn7O12 with Aluminum powder. Below its Neel temperature TN1 all magnetic reflections can be indexed by a single commensurate propagation vector k = (0, 0, 1). This is different to the case of CaMn7O12 where the propagation vector is incommensurate and where an in-plane helical magnetic structure has been found. We observe a commensurate non-collinear magnetic structure in CdMn7O12 with in-plane aligned magnetic moments resembling the ones in CaMn7O12. However, the commensurate propagation vector prevents the appearance of a helical magnetic structure in CdMn7O12. Finally, we also observe a third structural phase transition below ~60 K that can be attributed to phase separation.

76 citations


Journal ArticleDOI
TL;DR: In this paper, the critical magnetic field for the transition from the antiferromagnetic (AF) to the spin-flop (SF) phase obtained with magnetization and susceptibility measurements is investigated.
Abstract: NiO is a room-temperature antiferromagnetic (AF) insulator with important applications in AF spintronics. Although it is considered a prototypical AF material with a simple magnetic structure with two sublattice spins aligned in easy planes and having small in-plane magnetic anisotropy, its critical behavior has not been studied in detail. Here we present an experimental investigation of the critical magnetic field for the transition from the AF to the spin-flop (SF) phase obtained with magnetization and susceptibility measurements. The measured temperature dependence of the AF-SF critical field can be quite well explained by the instability of the low-lying magnon mode with energy renormalized by four-magnon interactions.

71 citations


Journal ArticleDOI
TL;DR: Single-crystal neutron diffraction shows that the magnetic propagation vector is k = [Formula] with the moments mostly along the [Formula: see text] axis and with a small component along the “small component” axis, which largely verifies the previously-published magnetic structure for this compound.
Abstract: The magnetic properties and magnetic structure are presented for CoPS3, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Neel temperature of [Formula: see text] K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2 K and 300 K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Single-crystal neutron diffraction shows that the magnetic propagation vector is k = [Formula: see text] with the moments mostly along the [Formula: see text] axis and with a small component along the [Formula: see text] axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent [Formula: see text] for [Formula: see text].

71 citations


Journal ArticleDOI
TL;DR: It is shown that single crystals of uranium dioxide subjected to strong magnetic fields along threefold axes in the magnetic state exhibit the abrupt appearance of positive linear magnetostriction, leading to a trigonal distortion, demonstrating a robust magneto-elastic memory that makes uranium dioxide the hardest piezomagnet known.
Abstract: The thermal and magnetic properties of uranium dioxide, a prime nuclear fuel and thoroughly studied actinide material, remain a long standing puzzle, a result of strong coupling between magnetism and lattice vibrations. The magnetic state of this cubic material is characterized by a 3-k non-collinear antiferromagnetic structure and multidomain Jahn-Teller distortions, likely related to its anisotropic thermal properties. Here we show that single crystals of uranium dioxide subjected to strong magnetic fields along threefold axes in the magnetic state exhibit the abrupt appearance of positive linear magnetostriction, leading to a trigonal distortion. Upon reversal of the field the linear term also reverses sign, a hallmark of piezomagnetism. A switching phenomenon occurs at ±18 T, which persists during subsequent field reversals, demonstrating a robust magneto-elastic memory that makes uranium dioxide the hardest piezomagnet known. A model including a strong magnetic anisotropy, elastic, Zeeman, Heisenberg exchange, and magnetoelastic contributions to the total energy is proposed. The nuclear fuel uranium dioxide is of intrinsic interest due to its industrial applications but it also exhibits intriguing electronic and magnetic properties. Here, the authors demonstrate how its complex magnetic structure and interactions give rise to a strong piezomagnetic effect.

61 citations


Journal ArticleDOI
TL;DR: It is discovered that the SkHE is depressed by modifying the magnetic structure at the edge of a track, and thus the skyrmion can move in almost a straight line at a high speed.
Abstract: Magnetic skyrmions have potential applications in novel information devices with excellent energy efficiency. However, the skyrmion Hall effect (SkHE) could cause skyrmions moving in a nanotrack to get annihilated at the track edge. In this work, we discovered that the SkHE is depressed by modifying the magnetic structure at the edge of a track, and thus the skyrmion can move in almost a straight line at a high speed. Unlike the inner part of a track with perpendicular magnetic anisotropy, the edge layer exhibits in-plane magnetic anisotropy, and the orientation of edge moments is opposite that at the perimeter of skyrmions nearby. As a result, an enhanced repulsive force acts on the skyrmion to oppose the Magnus force that causes the SkHE. Additionally, the Dzyaloshinskii–Moriya interaction (DMI) constant of the edge layer also matters. When there is no DMI at the edge layer, the transverse displacement of the skyrmion can be depressed effectively when the width of the edge layer is sufficiently large. However, when the inner part and the edge share the same DMI constant, non-monotonically varied transverse displacement occurs because of the Neel-wall-like structure at the edge layer.

55 citations


Journal ArticleDOI
TL;DR: In this article, a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology.
Abstract: This paper reveals how the electronic structure, magnetic structure, and topological phase of two-dimensional (2D), single-layer structures of bismuth are modified by point defects. We first showed that a free-standing, single-layer, hexagonal structure of bismuth, named h-bismuthene, exhibits nontrivial band topology. We then investigated interactions between single foreign adatoms and bismuthene structures, which comprise stability, bonding, electronic structure, and magnetic structures. Localized states in diverse locations of the band gap and resonant states in band continua of bismuthene are induced upon the adsorption of different adatoms, which modify electronic and magnetic properties. Specific adatoms result in reconstruction around the adsorption site. Single vacancies and divacancies can form readily in bismuthene structures and remain stable at high temperatures. Through rebondings, Stone-Whales-type defects are constructed by divacancies, which transform into a large hole at high temperature. Like adsorbed adatoms, vacancies induce also localized gap states, which can be eliminated through rebondings in divacancies. We also showed that not only the optical and magnetic properties, but also the topological features of pristine h-bismuthene can be modified by point defects. The modification of the topological features depends on the energies of localized states and also on the strength of coupling between point defects.

54 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic properties of phase-separated La 0.4 Dy 0.1 Ca 0.5 MnO 3 polycrystalline bulk sample have been investigated.

50 citations


Journal ArticleDOI
TL;DR: The results of MFM measurements performed under in-plane magnetic field demonstrate that it is possible to switch from the multivortex configuration to a single vortex configuration with low magnetic fields.
Abstract: Cylindrical nanowires synthesized by controlled electrodeposition constitute excellent strategic candidates to engineer magnetic domain configurations. In this work, multisegmented CoNi/Ni nanowires are synthesized for tailoring a periodic magnetic structure determined by the balance between magnetocrystalline and magnetostatic energies. High-resolution Transmission Electron Microscopy confirms the segmented growth and the sharp transition between layers. Although both CoNi and Ni segments have similar fcc cubic crystal symmetry, their magnetic configuration is quite different as experimentally revealed by Magnetic Force Microscopy (MFM) imaging. While the Ni segments are single domain with axial magnetization direction, the CoNi segments present two main configurations: a single vortex state or a complex multivortex magnetic configuration, which is further interpreted with the help of micromagnetic simulations. This original outcome is ascribed to the tight competition between anisotropies. The almost monocrystalline fcc structure of the CoNi segments, as revealed by the electron diffraction patterns, which is atypical for its composition, contributes to balance the magnetocrystalline and shape anisotropies. The results of MFM measurements performed under in-plane magnetic field demonstrate that it is possible to switch from the multivortex configuration to a single vortex configuration with low magnetic fields.


Journal ArticleDOI
TL;DR: The magnetic properties and magnetic structure for CoPS$_3, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Neel temperature of $T_N \sim 120$ K, were presented in this article.
Abstract: The magnetic properties and magnetic structure are presented for CoPS$_3$, a quasi-two-dimensional antiferromagnet on a honeycomb lattice with a Neel temperature of $T_N \sim 120$ K. The compound is shown to have XY-like anisotropy in its susceptibility, and the anisotropy is analysed to extract crystal field parameters. For temperatures between 2 K and 300 K, no phase transitions were observed in the field-dependent magnetization up to 10 Tesla. Single-crystal neutron diffraction shows that the magnetic propagation vector is {\bf{k}}= $\left[010\right]$ with the moments mostly along the $\mathbf{a}$ axis and with a small component along the $\mathbf{c}$ axis, which largely verifies the previously-published magnetic structure for this compound. The magnetic Bragg peak intensity decreases with increasing temperature as a power law with exponent $2\beta = 0.60 \pm 0.01$ for $T > 0.9~T_N$.

Journal ArticleDOI
TL;DR: In this paper, the stability, electronic and magnetic properties on Heusler alloys Zr(2)YZ (Y = Co, Cr, V and Z = Al, Ga, In, Pb, Sn, Tl).

Journal ArticleDOI
TL;DR: In this paper, the crystal chirality is reflected in the helicity of the magnetic structure by a one-to-one relationship, indicating that an antisymmetric exchange interaction mediated via the conduction electrons exists.
Abstract: Helical magnetic structures and their responses to external magnetic fields in Yb(Ni1−xCux)3Al9 with a chiral crystal structure of the space group R32 have been investigated by resonant X-ray diffraction It is shown that the crystal chirality is reflected in the helicity of the magnetic structure by a one-to-one relationship, indicating that an antisymmetric exchange interaction mediated via the conduction electrons exists When a magnetic field is applied perpendicular to the helical axis (c-axis), the second-harmonic peak of \((0,0,2q)\) develops with increasing field The third-harmonic peak of \((0,0,3q)\) has also been observed for the x = 006 sample This result provides strong evidence for the formation of a chiral magnetic soliton lattice state, a periodic array of chiral twist of spins, which has been suggested by the characteristic magnetization curve The helical ordering of magnetic octupole moments accompanying the magnetic dipole order has also been detected

Journal ArticleDOI
TL;DR: In this article, the optical conductivity of a newly discovered member of this family and a proposed Weyl semimetal (WSM) candidate with broken time reversal symmetry was investigated.
Abstract: Strong spin-orbit coupling (SOC) can result in ground states with nontrivial topological properties. The situation is even richer in magnetic systems where the magnetic ordering can potentially have strong influence over the electronic band structure. The class of $A{\mathrm{MnBi}}_{2}$ ($A$ = Sr, Ca) compounds are important in this context as they are known to host massive Dirac fermions with strongly anisotropic dispersion, which is believed to be due to the interplay between strong SOC and magnetic degrees of freedom. We report the optical conductivity of ${\mathrm{YbMnBi}}_{2}$, a newly discovered member of this family and a proposed Weyl semimetal (WSM) candidate with broken time reversal symmetry. Together with density functional theory (DFT) band-structure calculations, we show that the complex conductivity can be interpreted as the sum of an intraband Drude response and interband transitions. We argue that the canting of the magnetic moments that has been proposed to be essential for the realization of the WSM in an otherwise antiferromagnetically ordered system is not necessary to explain the optical conductivity. We believe our data is explained qualitatively by the uncanted magnetic structure with a small offset of the chemical potential from strict stochiometry. We find no definitive evidence of a bulk Weyl nodes. Instead, we see signatures of a gapped Dirac dispersion, common in other members of $A{\mathrm{MnBi}}_{2}$ family or compounds with similar 2D network of Bi atoms. We speculate that the evidence for a WSM seen in ARPES arises through a surface magnetic phase. Such an assumption reconciles all known experimental data.

Journal ArticleDOI
20 Jul 2017-ACS Nano
TL;DR: A comprehensive three-dimensional picture of magnetic ordering in high-density arrays of segmented FeGa/Cu nanowires is experimentally realized through the application of polarized small-angle neutron scattering, providing insight into the competing interactions and resulting stability windows for a variety of ordered magnetic structures.
Abstract: A comprehensive three-dimensional picture of magnetic ordering in high-density arrays of segmented FeGa/Cu nanowires is experimentally realized through the application of polarized small-angle neutron scattering. The competing energetics of dipolar interactions, shape anisotropy, and Zeeman energy in concert stabilize a highly tunable spin structure that depends heavily on the applied field and sample geometry. Consequently, we observe ferromagnetic and antiferromagnetic interactions both among wires and between segments within individual wires. The resulting magnetic structure for our nanowire sample in a low field is a fan with magnetization perpendicular to the wire axis that aligns nearly antiparallel from one segment to the next along the wire axis. Additionally, while the low-field interwire coupling is ferromagnetic, application of a field tips the moments toward the nanowire axis, resulting in highly frustrated antiferromagnetic stripe patterns in the hexagonal nanowire lattice. Theoretical calcul...

Journal ArticleDOI
TL;DR: The magnetic structures have been determined from the difference patterns between the neutron data in the paramagnetic and the magnetically ordered regions using a simulated annealing protocol and symmetry analysis techniques and further rationalized by means of ab initio DFT calculations.
Abstract: A study of the magnetic structure of the [NH2(CH3)2]n[FeIIIMII(HCOO)6]n niccolite-like compounds, with MII = CoII (2) and MnII (3) ions, has been carried out using neutron diffraction and compared with the previously reported FeII-containing compound (1). The inclusion of two different metallic atoms into the niccolite-like structure framework leads to the formation of isostructural compounds with very different magnetic behaviors due to the compensation or not of the different spins involved in each lattice. Below TN, the magnetic order in these compounds varies from ferrimagnetic behavior for 1 and 2 to an antiferromagnetic behavior with a weak spin canting for 3. Structure refinements of 2 and 3 at low temperature (45 K) have been carried out combining synchrotron X-ray and high-resolution neutron diffraction in a multipattern approach. The magnetic structures have been determined from the difference patterns between the neutron data in the paramagnetic and the magnetically ordered regions. These diffe...

Journal ArticleDOI
TL;DR: In this article, the authors investigated the dynamical properties of the triangular-lattice spin-1/2 antiferromagnet Ba$_3$CoSb$_2$O$_9$ in its one-third magnetization plateau phase using a combination of nonlinear spinwave theory and neutron scattering measurements.
Abstract: Magnetization plateaus in quantum magnets---where bosonic quasiparticles crystallize into emergent spin superlattices---are spectacular yet simple examples of collective quantum phenomena escaping classical description. While magnetization plateaus have been observed in a number of spin-1/2 antiferromagnets, the description of their magnetic excitations remains an open theoretical and experimental challenge. Here, we investigate the dynamical properties of the triangular-lattice spin-1/2 antiferromagnet Ba$_3$CoSb$_2$O$_9$ in its one-third magnetization plateau phase using a combination of nonlinear spin-wave theory and neutron scattering measurements. The agreement between our theoretical treatment and the experimental data demonstrates that magnons behave semiclassically in the plateau in spite of the purely quantum origin of the underlying magnetic structure. This allows for a quantitative determination of Ba$_3$CoSb$_2$O$_9$ exchange parameters. We discuss the implication of our results to the deviations from semiclassical behavior observed in zero-field spin dynamics of the same material and conclude they must have an intrinsic origin.

Journal ArticleDOI
TL;DR: In this article, the electronic structure, magnetism and optical properties of orthorhombic GdFeO3 in terms of density-functional-theory calculations have been investigated.
Abstract: Orthorhombic GdFeO3 has attracted considerable attention in recent years because its magnetic structure is similar to that of the well-known BiFeO3 material Here, we investigate the electronic structure, magnetism and optical properties of orthorhombic GdFeO3 in terms of density-functional-theory calculations The modified Becke-Johnson (mBJ) exchange potential is adopted to improve on the description of the electronic structure Our calculations show that the G-type antiferromagnetic (G-AFM ordering of Fe spins) phase of orthorhombic GdFeO3 is stable compared to other magnetic phases The semiconductor gap calculated with mBJ, substantially larger than that with GGA, is in good agreement with recent experimental values Additionally, we also investigate the effects of spin–orbit coupling on the electronic structure, and calculate the complex dielectric functions and other optical functions of photon energy The magnetic exchange interactions are also investigated, which gives a Neel temperature close to experimental observation For confirming these mBJ results, we also study the electronic structure of rhombohedral (R3c) BiFeO3 with mBJ, obtaining good consistency with experiment These lead to a satisfactory theoretical understanding of the electronic structure, magnetism and optical properties of orthorhombic GdFeO3 and can help elucidate the electronic structures and optical properties of other similar materials

Journal ArticleDOI
TL;DR: The ability to control electrical properties and magnetism by varying the crystal structure using the effect of the A-site cation in oxygen-deficient perovskites has been studied and the transformation of charge transport properties, where the metallic behavior of the Sr2 compound is converted into semiconductivity in the CaSr material is revealed.
Abstract: The ability to control electrical properties and magnetism by varying the crystal structure using the effect of the A-site cation in oxygen-deficient perovskites has been studied in AA′Fe2O6−δ, where A = Sr, Ca and A′ = Sr. The structure of Sr2Fe2O6−δ, synthesized at 1250 °C in air, contains dimeric units of FeO5 square pyramids separated by FeO6 octahedra. Here we show that this ordering scheme can be transformed by changing the A-site cations from Sr to Ca. This leads to a structure where layers of corner-sharing FeO6 octahedra are separated by chains of FeO4 tetrahedra. Through systematic variation of the A-site cations, we have determined the average ionic radius required for this conversion to be ∼1.41 A. We have demonstrated that the magnetic structure is also transformed. The Sr2 compound has an incommensurate magnetic structure, where magnetic moments are in spin-density wave state, aligning perpendicular to the body diagonal of the unit cell. With the aid of neutron diffraction experiments at 10 ...

Journal ArticleDOI
TL;DR: Polycrystalline NdFe0.5Cr 0.5O3 has orthorhombic structure with Pnma space group and is magnetically ordered at room temperature as confirmed by neutron diffraction as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the three-dimensional (3D) Fe/C hollow microspheres are constructed by iron nanocrystals permeating inside carbon matrix with a saturation magnetization of 340 emu/g, which is 1.55 times as that of bulk Fe.
Abstract: Materials with a high saturation magnetization have gained increasing attention in the field of microwave absorption; therefore, the magnetization value depends on the magnetic configuration inside them. However, the broad-band absorption in the range of microwave frequency (2-18 GHz) is a great challenge. Herein, the three-dimensional (3D) Fe/C hollow microspheres are constructed by iron nanocrystals permeating inside carbon matrix with a saturation magnetization of 340 emu/g, which is 1.55 times as that of bulk Fe, unexpectedly. Electron tomography, electron holography, and Lorentz transmission electron microscopy imaging provide the powerful testimony about Fe/C interpenetration and multi-domain state constructed by vortex and stripe domains. Benefiting from the unique chemical and magnetic microstructures, the microwave minimum absorption is as strong as −55 dB and the bandwidth (<−10 dB) spans 12.5 GHz ranging from 5.5 to 18 GHz. Morphology and distribution of magnetic nano-domains can be facilely re...

Journal ArticleDOI
TL;DR: In this paper, it was shown that at certain geometrical conditions, the circular dichroism of the diffraction vanishes completely, revealing a one-to-one correspondence with the spin structure.
Abstract: Long-wavelength spin spiral structures are ubiquitous in a large variety of magnetic materials. The detailed magnetic structure can take many variations owing to their different physical origins. Therefore, the unambiguous structural determination is crucial for understanding these spin systems, though such a task is experimentally challenging. Here, we show that ordered spin spiral structures can be fully determined in a single measurement by dichroic resonant elastic x-ray scattering using circularly polarized light. It is found that at certain geometrical conditions, the circular dichroism of the diffraction vanishes completely, revealing a one-to-one correspondence with the spin structure. We demonstrate both theoretically and experimentally this experimental principle, which allows for unambiguous structure determination immediately from the measured signal, whereby no modeling-based data refinement is needed. This largely expands the capabilities of conventional magnetic characterization techniques.

Journal ArticleDOI
TL;DR: In this article, the static magnetic properties and memory and exchange bias effects have been studied in sol-gel prepared La0.67Sr0.33MnO3 (LSMO) nanoparticles.
Abstract: The static magnetic properties and memory and exchange bias effects have been studied in sol-gel prepared La0.67Sr0.33MnO3 (LSMO) nanoparticles. Transmission electron microscopy (TEM) micrographs and static magnetization show log-normal particle and magnetic size distributions with a core-shell structure. Analysis of the magnetization measurements indicates the presence of a magnetic structure with a 7.8 nm core radius and a magnetic dead layer of thickness 1.6 nm in the LSMO nanoparticles, which comprises about 40% of the volume. The disordered spins in the shell freeze at lower temperatures than the core and produce a surface spin glass state exhibiting a weak exchange bias effect. Field cooled and zero-field cooled magnetization measurements have been carried out to study the slow dynamics of the sample and associated magnetic memory effects; the results reveal the superparamagnetic behavior of LSMO nanoparticles described in terms of the magnetic size distribution rather than a superspin glass state.

Journal ArticleDOI
TL;DR: This work shows that antiferromagnetic Mn5Si3 single crystals exibit a large AHE which is strongly anisotropic and shows multiple transitions with sign changes at different magnetic fields due to field-induced rearrangements of the magnetic structure despite only tiny variations of the total magnetization.
Abstract: The anomalous Hall effect (AHE), which in long-range ordered ferromagnets appears as a voltage transverse to the current and usually is proportional to the magnetization, often is believed to be of negligible size in antiferromagnets due to their low uniform magnetization. However, recent experiments and theory have demonstrated that certain antiferromagnets with a non-collinear arrangement of magnetic moments exhibit a sizeable spontaneous AHE at zero field due to a non-vanishing Berry curvature arising from the quantum mechanical phase of the electron's wave functions. Here we show that antiferromagnetic Mn5Si3 single crystals exibit a large AHE which is strongly anisotropic and shows multiple transitions with sign changes at different magnetic fields due to field-induced rearrangements of the magnetic structure despite only tiny variations of the total magnetization. The presence of multiple non-collinear magnetic phases offers the unique possiblity to explore the details of the AHE and the sensitivity of the Hall effect on the details of the magnetic texture.

Journal ArticleDOI
TL;DR: Analysis of different mechanisms of spin and hyperfine interactions in 3R-Ag FeO2 and its structural analogue CuFeO2 points to a specific role played by the topology of the exchange coupling and the oxygen polarization in the delafossite-like structures.
Abstract: We report new results of a 57Fe Mossbauer study of hyperfine magnetic interactions in the layered multiferroic 3R-AgFeO2 demonstrating two magnetic phase transitions at T N1 and T N2. The asymptotic value β * ≈ 0.34 for the critical exponent obtained from the temperature dependence of the hyperfine field H hf(T) at 57Fe the nuclei below T N1 ≈ 14 K indicates that 3R-AgFeO2 shows quasi-3D critical behavior. The spectra just above T N1 (T N1 < T < T * ≈ 41 K) demonstrate a relaxation behavior due to critical spin fluctuations which indicates the occurrence of short-range correlations. At the intermediate temperature range, T N2 < T < T N1, the 57Fe Mossbauer spectra are described in terms of collinear spin-density-waves (SDW) with the inclusion of many high-order harmonics, indicating that the real magnetic structure of the ferrite appears to be more complicated than a pure sinusoidally modulated SDW. Below T < T N2 ≈ 9 K, the hyperfine field H hf reveals a large spatial anisotropy (ΔH anis ≈ 30 kOe) which is related with a local intra-cluster (FeO6) spin-dipole term that implies a conventional contribution of the polarized oxygen ions. We proposed a simple two-parametric formula to describe the dependence of H anis on the distortions of the (FeO6) clusters. Analysis of different mechanisms of spin and hyperfine interactions in 3R-AgFeO2 and its structural analogue CuFeO2 points to a specific role played by the topology of the exchange coupling and the oxygen polarization in the delafossite-like structures.

Journal ArticleDOI
TL;DR: In this paper, a single-crystal neutron diffraction and inelastic neutron scattering study on the spin 1/2 cuprate was performed, where the authors determined the nature of the structural transition occurring at 115 K, the magnetic structure below 25 K resolved in the updated space group, and the microscopic ingredients at the origin of this magnetic arrangement.
Abstract: We report a single-crystal neutron diffraction and inelastic neutron scattering study on the spin 1/2 cuprate ${\mathrm{Cu}}_{3}\mathrm{Bi}{({\mathrm{SeO}}_{3})}_{2}{\mathrm{O}}_{2}\mathrm{Cl}$, complemented by dielectric and electric polarization measurements. The study clarifies a number of open issues concerning this complex material, whose frustrated interactions on a kagomelike lattice, combined with Dzyaloshinskii-Moriya interactions, are expected to stabilize an exotic canted antiferromagnetic order. In particular, we determine the nature of the structural transition occurring at 115 K, the magnetic structure below 25 K resolved in the updated space group, and the microscopic ingredients at the origin of this magnetic arrangement. This was achieved by an analysis of the measured gapped spin waves, which signifies the need for an unexpected and significant anisotropic exchange beyond the proposed Dzyaloshinskii-Moriya interactions. Finally, we discuss the multiferroic properties of this material with respect to the space group symmetries.

Journal ArticleDOI
TL;DR: In this paper, the temperature evolution of the magnetic structures of HoFeO3 was investigated by single crystal neutron diffraction, and the three different magnetic structures were found as a function of temperature for Ho FeO3.
Abstract: We have investigated the temperature evolution of the magnetic structures of HoFeO3 by single crystal neutron diffraction. The three different magnetic structures werevfound as a function of temperature for HoFeO3. In all three phases the fundamental coupling between the Fe sub-lattices remains the same and only their orientation and the degree of canting away from the ideal axial direction varies. The magnetic polarisation of the Ho sub-lattices in these two higher temperature regions, in which the major components of the Fe moment lie along x and y, is very small. The canting of the moments from the axial directions is attributed to the antisymmetric interactions allowed by the crystal symmetry. In the low temperature phase two further structural transitions are apparent in which the spontaneous magnetisation changes sign with respect to the underlying antiferromagnetic configuration. In this temperature range the antisymmetric exchange energy varies rapidly as the the Ho sub-lattices begin to order. So long as the ordered Ho moments are small the antisymmetric exchange is due only to Fe-Fe interactions, but as the degree of Ho order increases the Fe-Ho interactions take over whilst at the lowest temperatures, when the Ho moments approach saturation the Ho-Ho interactions dominate. The reversals of the spontaneous magnetisation found in this study suggest that in HoFeO3 the sums of the Fe-Fe and Ho-Ho antisymmetric interactions have the same sign as one another, but that of the Ho-Fe terms is opposite.

Journal ArticleDOI
TL;DR: This work unravels the importance of addressing quantitatively the effect of stray magnetic fields from both, the superconductor and the ferromagnet in hybrid magnetic nano-devices based on high temperature superconductors.
Abstract: Superconductivity and ferromagnetism are two antagonistic phenomena that combined can lead to a rich phenomenology of interactions, resulting in novel physical properties and unique functionalities. Here we propose an original hybrid system formed by a high-temperature superconducting film, patterned with antidots, and with ferromagnetic nano-rods grown inside them. This particular structure exhibits the synergic influence of superconductor (SC) - ferromagnetic (FM) stray fields, in both the superconducting behaviour of the film and the three-dimensional (3D) magnetic structure of nano-rods. We show that FM stray fields directly influence the critical current density of the superconducting film. Additional functionalities appear due to the interaction of SC stray fields, associated to supercurrent loops, with the non-trivial 3D remanent magnetic structure of FM nano-rods. This work unravels the importance of addressing quantitatively the effect of stray magnetic fields from both, the superconductor and the ferromagnet in hybrid magnetic nano-devices based on high temperature superconductors.