Showing papers on "Magnetic structure published in 1990"
TL;DR: A second-variation full-potential linear augmented-plane-wave total-energy method for thin-film ferromagnetic systems is used to study the spin-orbit-interaction contribution to the magnetic anisotropy.
Abstract: A second-variation full-potential linear augmented-plane-wave total-energy method for thin-film ferromagnetic systems is used to study the spin-orbit-interaction contribution to the magnetic anisotropy. For a free-standing Fe monolayer, the spin magnetization is determined to lie in the plane. Results for Fe monolayers on Au(001), Ag(001), and Pd(001) substrates indicate a preference for the spin direction to be perpendicular to the plane of the film. Computational details for this magnetic anisotropy are also discussed.
202 citations
TL;DR: In this article, the magnetic structures of substituted ferrites are reviewed, focusing on the more usual case of a local canted state, and experimental phase diagrams (tetrahedral-octahedral iron concentrations) are established to distinguish between different magnetic regions.
Abstract: In this paper the magnetic structures of various substituted ferrites are reviewed. Attention is focused on the more usual case of a local canted state. Several systems and detailed magnetic experiments are listed and discussed. Then experimental phase diagrams (tetrahedral-octahedral iron concentrations) are established to distinguish between different magnetic regions: ferrimagnetic order, local canted state or perturbed magnetic order, spin-glass-like phase and in between intermediate regions.
201 citations
TL;DR: In this paper, the authors examined relative stability and physical properties of several possible magnetic states in the mean field theory for an itinerant electron model, i.e., the Hubbard model on a two-dimensional square lattice.
Abstract: Spatially modulated magnetic phases are investigated within the mean field theory for an itinerant electron model, i.e. the Hubbard model on a two-dimensional square lattice. By numerically diagonalizing the Hamiltonian for finite-size systems under a periodic boundary condition, we examine relative stability and physical properties of several possible magnetic states. When the electron fillings are nearly half-full, the diagonally or vertically modulated spin density wave (SDW) state is stabilized over the uniform antiferromagnetic state and a crossover from the vertical to the diagonal states appears. The diagonal or vertical stripe state is characterized by the presence of the midgap band due to the soliton lattice formation inside the main SDW gap, being an insulator. The wave length λ SDW is linearly proportional to the excess carrier concentration. Excess carriers are accommodated in the form of the soliton lattice, forming a charge density wave whose wave length is λ SDW /2.
194 citations
TL;DR: In this article, generalized polarization analysis has been used to re-examine the triangular magnetic structure of Mn3Sn. The analysis shows unambiguously that a structure allowing three trigonal domains is necessary to account for the scattered polarizations.
Abstract: The newly developed technique of generalized polarization analysis has been used to re-examine the triangular magnetic structure of Mn3Sn. The magnitude and direction of the polarization of neutrons scattered by some mixed magnetic and nuclear Bragg reflections at 200 K have been measured for a range of different incident polarization directions using a zero-field polarimeter. The results have been used to discriminate between different models which have been proposed for the magnetic structure. The analysis shows unambiguously that a structure allowing three trigonal domains is necessary to account for the scattered polarizations. Of the models suggested up to now only the 'inverse triangle' structure satisfies this criterion. The manganese moment was determined to be 3.00(1) mu B much larger than the value (1.78 mu B) given by earlier measurements of the flipping ratios in an applied field. On cooling below 50 K the polarization analysis gave evidence for a transition to a magnetic structure with a significant ferromagnetically aligned moment parallel to (001).
135 citations
TL;DR: In this article, the average-valence phase of the rhombohedrally distorted perovskite Sr{sub 2}LaFe{sub 3}O{sub 8.94} has been refined from neutron powder diffraction data collected at room temperature (spacegroup R{bar 3}c, a = 5.4580 {angstrom}, {alpha} = 60.19{degree}.
135 citations
TL;DR: In this article, an S = 3/2 Heisenberg antiferromagnet on a triangular lattice of magnetic Cr atoms is studied by neutron powder diffraction, and it is shown that magnetic Bragg scattering is distributed on a line (1/31/3 zeta ), where zeta takes integer values.
Abstract: An S=3/2 Heisenberg antiferromagnet on a triangular lattice CuCrO2, in which stacking of the triangular lattice of magnetic Cr atoms forms a layered rhombohedral antiferromagnet, is studied by neutron powder diffraction. In the paramagnetic phase the powder diffraction pattern shows asymmetry, which proves a two-dimensional character. In the ordered phase, magnetic Bragg scattering has large width, indicating that the scattering is distributed on a line (1/31/3 zeta ) with peaks where zeta takes integer values. Although the magnetic long-range order is established in the c plane, correlation in the c direction is finite or the modulation vector is distributed on the line. Intensity of magnetic reflections is consistent with the 120 degrees structure in the a-c plane with moment (3.1+or-0.2) mu B.
115 citations
TL;DR: In this article, the crystal structure of Li2CuO2 has been investigated and its magnetic structure solved by neutron powder diffraction, and the magnetic moment of copper atoms at 1.5 K is 0.96(4)microB, which is very close to the saturation moment of spin only Cu+2 (d9).
108 citations
TL;DR: The spatial distribution of magnetisation density in the intermetallic compound Mn5Ge3 has been determined from a polarised neutron diffraction single-crystal study at 4.2 K.
Abstract: The spatial distribution of magnetisation density in the intermetallic compound Mn5Ge3 has been determined from a polarised neutron diffraction single-crystal study at 4.2 K. The positional and thermal parameters of the structure were derived from an unpolarised neutron study at 60 K, which also served to characterise the extinction in the material. The observed magnetic structure factors were fitted by a multipole expansion based on free-atom form factors for each of the two crystallographically inequivalent manganese atoms in the unit cell. The magnetic moment of the Mn1 atom with site symmetry 32 is 1.96(3) mu B and that of Mn2 with site symmetry mm is 3.23(2) mu B. The radial form factor of the Mn1 atom is found to be significantly contracted relative to that of a free Mn2+ ion. Evidence is presented that Mn-Mn interactions are the major factor leading to the difference in the moments on the two sites.
103 citations
TL;DR: In this paper, the magnetic properties of four intermetallic compounds, e, e 1, κ and η, in manganese-germanium system are studied by means of magnetization measurement and neutron diffraction.
Abstract: Magnetic properties of four intermetallic compounds, e, e 1 , κ and η, in manganese-germanium system are studied by means of magnetization measurement and neutron diffraction. Exchange coefficients of the interaction between Mn atoms in the compounds are estimated quantitatively using the molecular field approximation, based on the localized moment model. The exchange coefficient between Mn atoms on different sublattices is found to depend largely on the interatomic distance: The exchange coefficient is found to be negative for smaller interatomic distances than r c =2.9 A and positive for larger distances. The magnitude of atomic magnetic moment in the compounds is consistently discussed using the Pauling valence, after Mori and Mitsui (J. Phys. Soc. Jpn. 25 (1968) 82).
81 citations
TL;DR: The magnetic properties of R2PdSi3 compounds, where R is Pr, Nd, Gd, Tb, Dy, Ho, Er, Tm and Y, have been investigated from 4.2 to 300 K as discussed by the authors.
77 citations
TL;DR: In this article, the 6H perovskites Ba3NiRu2O9 and Ba3CoRu 2O9 have been refined from neutron powder diffraction data collected at 5 or 2 K.
TL;DR: In this paper, the electronic structure of CoMnGe was calculated for hexagonal and orthorhombic structures by the self-consistent KRR method within the LSD approximation.
TL;DR: The crystal and magnetic structures of the perovskite Sr 2 LaFe 3 O 8 (space group Pmma, a = 5.5095(1), b = 11.8845(5), c = 5,6028(1) AA) have been refined from X-ray and neutron powder diffraction data collected at room temperature as discussed by the authors.
TL;DR: In this paper, the structural and magnetic properties of stoichiometric Nd2NiO4 have been investigated in the presence of a ferromagnetic component along c-axis in the Ni2+ spin structure.
Abstract: Neutron diffraction on polycrystalline samples of stoichiometric Nd2NiO4 shows a complex structural and magnetic behaviour as a function of temperature. The room temperature (RT) phase is orthorhombic (Bmab) and Ni2+ ions are 3D antiferromagnetically ordered (TN ≈ 320 K), with a propagation vector k = [100] and spins oriented parallel to the propagation vector, i.e. along the a-axis. The magnetic structure can be described as a gx mode (Shubnikov group BPmab'). The magnetic moment for Ni2+ is 1.57μB at 160 K. The system undergoes a structural phase transition from orthorhombic to tetragonal (P42/ncm) at T1 ≈ 130 K. The tetragonal phase allows the existence of a ferromagnetic component along c-axis in the Ni2+ spin structure, the magnetic structure can be described either as a gxcyfz mode (Shubnikov group (Pc' c' n) or as a gx + cyfz mode (Shubnikov group P42/nc' m'). At a temperature as high as 70 K the polarization of the Nd3+ ions becomes noticeable. At low temperature (TN ≈ 8 K) Nd3+ ions cooperative order takes place with a magnetic moment of 3.2μB at 1.5 K and a magnetic structure belonging to the same Shubnikov group (either Pc' c' n or P42/nc' m'). Fully oxidized samples of Nd2NiO4+δ as obtained in air atmosphere, seems to be also orthorhombic at RT and do not show static magnetic order or structural phase transitions between 1.5 K and 300 K. Partially oxidized samples (δ = 0.04) are also orthorhombic at RT, and show a similar magnetic behaviour as stoichiometric ones, but no structural phase transition at low temperatures is observed.
TL;DR: In this paper, the magnetic moments distribution and the interlayer magnetic couplings between ferromagnetic layers Am (A=Fe or Co) coupled by non-magnetic (B=V or Ru), nearly ferromag or antiferromagnetic (B =Cr) spacer layers Bn are obtained as a function of the spacer thickness n.
Abstract: The general trends for the electronic structure of perfect model superlattices AmBn are calculated using a real-space tight·binding model. The magnetic moments distribution and the interlayer magnetic couplings between ferromagnetic layers Am (A=Fe or Co) coupled by non-magnetic (B=V or Ru), nearly ferromagnetic (B=Pd) or antiferromagnetic (B=Cr) spacer layers Bn are obtained as a function of the spacer thickness n. In a first part, we present the model we used for the calculation and the crystallographic structure of the considered superlattices (Fe/V, Fe/Cr, Co/Ru and Co/Pd). These considera tions will be applied to the non·magnetic and nearly ferromagnetic cases to derive general trends for the magnetic interlayers couplings. In a second part, we apply the method we presented previously to the superlattices with an antiferromagnetic spacer (Fe,Cr.). Using first a "d" band calculation we show that the interlayer coupling energy can be understood in terms of a strong interfacial antifer romagnetic coupling and of a constrained magnetic wall in the Cr layer giving a rapidly oscillating coupling energy. An extension of the previous calculation taking into account the "spd" hybridization does not affect the previous conclusion. Finally we examine the distribu tion of magnetic moments and the stability of tilted antiferromagnetic Cr layers and we find that this magnetic structure is nearly degenerate with the collinear antiferromagnetic arrangement.
TL;DR: The magnetic phases when a magnetic field is applied in the plane of the helical magnetic structure of Ho are identified with structures, intermediate between the helix and the fan, which are called helifans.
Abstract: The magnetic phases which have earlier been observed when a magnetic field is applied in the plane of the helical magnetic structure of Ho are identified with structures, intermediate between the helix and the fan, which we call helifans. A number of helifan structures have been calculated by a self-consistent mean-field method, and one of them accounts very well for the observed neutron-diffraction pattern. Different sequences of helifans may, in principle, be produced by varying the magnetic field and temperature, and modifying the exchange by alloying.
TL;DR: The magnetic ordering of R2BaNiO5 (R Y, Er) has been studied by neutron powder diffraction as mentioned in this paper, and the results show that the Ni-Er interactions are predominant between 33 and 16 K, and, at lower temperatures, cooperative Er-Er interaction leads to a saturation of the Er3+ ordered moments at T = 4 K.
TL;DR: Simultaneous refinement of the room-temperature x-ray and neutron-diffraction data was used to obtain accurate cell parameters and atomic positions, and ESR signals can be associated with antiferromagnetic resonance modes, consistent with an ordered antiferromeagnetic phase.
Abstract: The results of an investigation of ${\mathrm{Bi}}_{2}$${\mathrm{CuO}}_{4}$ using x-ray and neutron powder diffraction, dc magnetometry, and electron-spin resonance are presented. Simultaneous refinement of the room-temperature x-ray and neutron-diffraction data was used to obtain accurate cell parameters and atomic positions. Neutron-diffraction data at 13 and 300 K show that the appropriate space group is P4/ncc at both temperatures and reveal the appearance at the lower temperature of two magnetic peaks, which can be indexed as (100) and (210) reflections. While they are clearly indicative of long-range antiferromagnetic order, on the basis of these powder data alone one cannot determine the moment direction. However, on the assumption that the moments lie along the c axis, the copper magnetic moment is (0.56\ifmmode\pm\else\textpm\fi{}0.04)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$. dc magnetometry was performed at temperatures from 1.66 to 400 K and fields ranging from 0.5 to 50 kOe. The magnetization showed no field saturation even at 1.66 K and 45 kOe. The susceptibility showed a maximum near 50.4 K with a Curie tail observed at low temperatures. Antiferromagnetic interactions dominated at all temperatures. The magnetic behavior is like that of a three-dimensional antiferromagnetic system. ESR experiments were done over the temperature range 4.3--300 K. For temperatures above 50 K, one broad line with g=2.09 was observed. The resonance field shifted to higher values for T37 K, with an eventual splitting of the line below 15 K. These ESR signals can be associated with antiferromagnetic resonance modes, consistent with an ordered antiferromagnetic phase.
TL;DR: In this paper, the authors performed diffraction experiments on Er 3 Si 5 silicide on a single crystal and a thin epitaxial layer, in agreement with the neutron data.
Abstract: Neutron diffraction experiments have been performed on Er 3 Si 5 silicide. The crystallographic structure of this compound is orthorhombic, the magnetic structure is non-collinear. Magnetic measurements on a single crystal and a thin epitaxial layer give very similar results, in agreement with neutron data.
TL;DR: In this article, the authors show that the magnitude of the Ce ordered moment varies little from site to site; a nonmagnetic ground state for the Ce3+ ion is no longer required, and the extreme weakness of the harmonics is explained.
Abstract: The previously accepted spatially modulated magnetic structure of CeAl2 is shown to be incorrect. Neutron diffraction measurements in an applied magnetic field imply that the zero-field magnetic structure is spiral: however, the moments on the two Ce sublattices rotate in opposite senses. In the author's model, the magnitude of the Ce ordered moment varies little from site to site; a non-magnetic ground state for the Ce3+ ion is no longer required, and the extreme weakness of the harmonics is explained.
TL;DR: In this paper, the crystal structure of Bi2CuO4 has been investigated and its magnetic structure solved by neutron powder diffraction, which is perfectly described in the space group P4/ncc.
Abstract: The crystal structure of Bi2CuO4 has been reinvestigated and its magnetic structure solved by neutron powder diffraction. The crystal structure, according to earlier work, is perfectly described in the space group P4/ncc. Contrary to the dimeric magnetic behaviour suggested in a recent paper, the title compound becomes long-range antiferromagnetically ordered below 50 K. The ground state has Cz symmetry and the crystallographic magnetic group is P4/n'c'c'. The magnetic moment of copper atoms at 1.5 K is 0.93(6) mu B, which is very close to the saturation moment of spin-only Cu(II)(d9).
TL;DR: The change in the magnetic spin structure of simple domain configurations has been investigated as a function of grain size, shape and varying external magnetic fields at elevated temperatures in this article, and the results indicate that simplification of domain configuration occurs as grains become elongated, and as grain sizes increase from small pseudo-single-domain (PSD) to large PSD.
Journal Article•
TL;DR: In this article, a low temperature transition to a tetragonal structure exhibiting another tilting type has been observed for Pr 1−x Ba x MnO 3 (0.40) perovskites form at room temperature two different orthorhombic phases.
TL;DR: The 93 Nb NMR and magnetization have been measured to investigate the nature of weak antiferromagnetism in the hexagonal C-14 Laves phase compound, NbFe 2.
Abstract: The 93 Nb NMR and magnetization have been measured to investigate the nature of weak antiferromagnetism in the hexagonal C-14 Laves phase compound, NbFe 2 . The temperature and magnetic field dependence of the magnetization and nuclear spin-lattice relaxation time, T 1 , confirmed that an antiferromagnetic transition occurs at low fields and is easily suppressed by fields above 6 kOe. An analysis of T 1 shows that both the ferro- and antiferromagnetic spin fluctuations coexist in this system and that the ferromagnetic component is dominant at high fields. The coexistence of two components of the spin fluctuation may be related to the anomalous temperature dependence of the magnetic susceptibility at high temperatures. The analysis of NMR spectra suggests that the magnetic structure at the ordered state is of the spin density wave type giving rise to a large distribution of hyperfine field.
TL;DR: A microscopic study aimed at understanding the magnetic dynamics of several parent compounds (of the high-T, superconductors) in terms of subtle details of their structural characteristics, and shows that there are really two energy scales in the dy- namics, namely, J (=4t /U), the exchange energy, and Jr, where r is the ratio of an effective interplanar- to planar-hopping strength.
Abstract: It is shown that thermal excitation of spin waves in a highly anisotropic antiferromagnet results in a characteristic temperature dependence of sublattice magnetization with a crossover from a 3D to a quasi-2D behavior. The magnetic dynamics in several copper-oxide-based antiferromagnets is analyzed in this context in terms of subtle details of their structural characteristics, and the temperature depen- dence of the Cu moment is used to determine the planar and interplanar exchange energies. PACS numbers: 75.10.Lp, 75.30.Ds, 75.40.Gb neutron scattering, and the general trend expected from structural characteristics. For La2Cu04, we obtain Z,J = 1600 K, where Z, -1.16 is the renormalization of the spin-wave velocity. This is in agreement with the reported values for J in other works: 0. 16/Z, eV (neutron-scattering studies), 0. 14 eV (Raman scatter- ing), 0. 13 eV (by fitting the spin-correlation length within the nonlinear sigma model), 1450 K (by fitting the spin-correlation length within a Monte Carlo simula- tion of the spin- —, ' The remarkable manifestation of the almost 2D anti- ferromagnetism in high-T, cuprate superconductors has provided a great impetus in efforts to understand low- dimensional antiferromagnetism. Specifically, the dis- coveries of long-range antiferromagnetic (AF) order, ' spin-wave excitations, and long-range, 2D AF spin correlations above the Neel temperature3 have contribut- ed much to clarifying important theoretical issues. Thus, the 2D aspects of antiferromagnetism, manifested as T) Ttv, are beginning to be understood. However, in the temperature regime T( Ttv, where 3D AF ordering sets in, the weak interlayer magnetic coupling becomes a most relevant piece in the physics. The very weak interlayer coupling affords us with a high- ly anisotropic antiferromagnet, and therefore an investi- gation of how it controls the magnetic dynamics is of much interest. Furthermore, the magnetic interlayer coupling in the copper-oxide systems depends, in a very subtle manner, on details of their structural characteris- tics. For example, if it were not for the orthorhombic distortion in the La2Cu04 there would be no net ex- change coupling between two neighboring layers. Thus, as a supplement to the conductivity anisotropy, magnetic dynamics can be used as a probe to investigate magnetic aspects of the interlayer coupling, which is of importance in some theories of high-T, superconductivity. In this Letter we report a microscopic study aimed at understanding the magnetic dynamics of several parent compounds (of the high-T, superconductors) in terms of subtle details of their structural characteristics. We first examine, within an itinerant-electron model, the magnet- ic dynamics of thermally excited spin waves in a highly anisotropic antiferromagnet, as revealed in the tempera- ture dependence of sublattice magnetization M(T). We show that there are really two energy scales in the dy- namics, namely, J (=4t /U), the exchange energy, and Jr, where r is the ratio of an effective interplanar- to planar-hopping strength. For kgT & 2Jr, the magnetiza- tion falls off' as T, characteristic of a 3D system. How- ever, for kg T & 2Jr, we show that there is a crossover to a TlnT behavior, which is a quasi-2D behavior. We also fit the M(T) vs T behavior to experimental data for several systems and find the fits to be excellent. Moreover, the value obtained from the best fits for J and r are, respectively, in agreement with results known from
TL;DR: In this article, it was shown that a scanning tunneling microscope with a magnetic tip gives us the possibility to determine the spin directions of surface magnetic ions with atomic resolution, but the tip should not necessarily be a ferromagnet.
TL;DR: A simple theoretical model gives results in good agreement with the experimental measurements of an alternating-helicity phase where the magnetic unit cell is twice the length of the chemical unit cell.
Abstract: In this sytem competing exchange and Zeeman interactions lead to many different possible magnetic structures. Of particular interest is an alternating-helicity phase where the magnetic unit cell is twice the length of the chemical unit cell. A simple theoretical model gives results in good agreement with the experimental measurements
TL;DR: In this article, the substitution effects of Fe with Co on saturation magnetization and Curie temperature have been investigated, and a detailed analysis of crystallographic and magnetic arrangement is presented.
Abstract: The compounds YTi(Fe1−xCox)11 form complete solid solutions (0≤X≤1) all of which crystallize in the ThMn12‐type tetragonal structure. The substitution effects of Fe with Co on saturation magnetization and Curie temperature have been investigated. A neutron‐diffraction study has been carried out on YTiCo11 and YTi(Co0.5Fe0.5)11. A strong preferential site occupation for Co and Ti atoms is observed. A detailed analysis of crystallographic and magnetic arrangement is presented.
TL;DR: A first-principles theory for compositional and magnetic correlations in alloys is described and the results of the theory are compared with recent diffuse, unpolarized, neutron-scattering measurements on a single crystal of ferromagnetic Fe{ sub 0.865}V{sub 0.135}.
Abstract: We describe a first-principles theory for compositional and magnetic correlations in alloys and compare the results of the theory with recent diffuse, unpolarized, neutron-scattering measurements on a single crystal of ferromagnetic Fe{sub 0.865}V{sub 0.135}. The nuclear cross section is described very well by the theory and we are able to connect the {ital q}-dependent structure to the underlying electronic structure of the alloy. The magnetocompositional and magnetic correlations also may be obtained for comparison to polarized measurements.
TL;DR: In this paper, a stripe domain structure with a domain width of 220 nm is observed, the highest resolution of a periodic magnetic structure measured by MFM to date, and magnetic fine structure of typically 50 nm width and more than 200 nm length by measuring magnetic forces as small as 0.1 nN.
Abstract: The lateral resolution observed in recent MFM experiments on CoCr and FeNdB are compared and analyzed theoretically. On a Co80Cr20 thin film a stripe domain structure with a domain width of 220 nm is observed, the highest resolution of a periodic magnetic structure measured by MFM to this date, and magnetic fine structure of typically 50 nm width and more than 200 nm length by measuring magnetic forces as small as 0.1 nN. A resolution of 10 nm is obtained on rapidly quenched FeNdB, where domains with a typical size of 600–700 nm are observable. By comparing these measurements with simulations it is concluded that the lower resolution achieved on CoCr is to be expected as the domain size is similar to the typical spatial extent of the domain transition stray field.