Showing papers on "Magnetic structure published in 1989"
TL;DR: The magnetic ordering of a single crystal of the cubic polymorph of FeGe has been studied by small-angle neutron scattering as discussed by the authors, and the magnetic ordering in cubic FeGe is a Dzyaloshinskii spiral similar to the structure observed in the compound MnSi.
Abstract: The magnetic ordering of a single crystal of the cubic polymorph of FeGe has been studied by small-angle neutron scattering. The compound orders magnetically at TN=278.7 K into a long-range spiral (period approximately 683-700 AA) propagating along equivalent directions at high temperatures and along equivalent directions at low temperatures. The length of the spiral wavevector is nearly independent of temperature. The transition at TN is first order with very little hysteresis. The transition at which the direction of the spiral turns is rather sluggish. It takes place in a temperature interval of approximately 40 K and shows pronounced temperature hysteresis (T2 down arrow =211 K, T2 up arrow =245 K). Applied magnetic fields of 20-40 mT, depending on the temperature and the field direction, cause the spiral axis to turn into the direction of the applied field. As the field is further increased, the amplitude of the antiferromagnetic spiral decreases and the ferromagnetic component increases until at fields above approximately 200-300 mT cubic FeGe becomes magnetically saturated. The magnetic ordering in cubic FeGe is a Dzyaloshinskii spiral similar to the structure observed in the isostructural compound MnSi. However, in MnSi the spiral propagates along equivalent directions at all temperatures below TN=29.5 K.
246 citations
TL;DR: Among Cu/sup 2+/ compounds, cupric oxide (CuO) has unusual magnetic properties, some of which are shared by the superconducting copper oxides, and neutron scattering experiments on a CuO single crystal have been performed to study these properties.
Abstract: Among Cu/sup 2+/ compounds, cupric oxide (CuO) has unusual magnetic properties, some of which are shared by the superconducting copper oxides. In order to study these properties further, neutron scattering experiments on a CuO single crystal have been performed. Two magnetic phase transitions at T/sub N//sub 1/ = 231 K and T/sub N//sub 2/ = 212.5 K have been observed, with the magnetic structure below T/sub N//sub 2/ antiferromagnetic and the structure between T/sub N//sub 1/ and T/sub N//sub 2/ helical in nature. The dynamics of the magnetism was also studied. As in La/sub 2/CuO/sub 4/, the dispersion of the low-temperature spin-wave excitations is unusually steep (dE/dk = 250 +- 75 meV A/sup -1/), indicating strong magnetic interactions. Inelastic magnetic scattering has also been measured above T/sub N//sub 1/. At temperatures slightly above the 231-K phase transition, dynamic critical slowing has been observed.
215 citations
TL;DR: In this paper, the critical size for transformation from a uniform single-domain structure to a non-uniform three-dimensional structure is about 0.1 µm for magnetite.
Abstract: The fidelity of magnetic recording materials (whether they be synthetic crystals on a recording tape, or natural crystals in rocks recording changes in the Earth's magnetic field) depends on the uniformity of their magnetic structure. Such structure is determined by minimizing the energies arising from atomic magnetic dipole interactions. Previous micromagnetic models of coupled spin structures have contained well defined constraints to make the calculations tractable. By using a supercomputer, we have been able to perform unconstrained calculations of minimum energy structures for cubic assemblies of up to 22×22×22 exchange-coupled spins. The critical size for transformation from a uniform single-domain structure to a non-uniform three-dimensional structure is about 0.1 µm for magnetite, as found previously from one-dimensional modelling. However, a variety of different non-uniform structures are possible, with energies and magnetic moments much less than those of conventional lamellar domains. The predicted moments of unweighted combinations of these states agree well with experimental measurements on magnetite in the size range 0.08-0.5 μm. Surface spin structures are such as to minimize flux leakage out of the particle and might be misleadingly imaged by the Bitter colloid technique as indicating a single-domain state.
167 citations
TL;DR: In this article, the magnetic structure of the cubic gamma-Fe100-xCox (x < 4) alloy precipitates is studied by neutron diffraction, and spin-density wave (SDW) propagating along the cubic axis is found for these specimens.
Abstract: An X-ray diffraction study reveals that an introduction of a small amount of Co suppresses the structural phase transition of gamma -Fe precipitates in Cu and the cubic gamma -FeCo alloy precipitates are available even at the lowest temperature. The magnetic structure of the cubic gamma -Fe100-xCox (x<4) alloy precipitates is studied by neutron diffraction, and spin-density wave (SDW) propagating along the cubic axis is found for these specimens. The Neel temperature and wavelength of the SDW decrease with increasing Co concentration. It is demonstrated that the magnetic structure of the cubic gamma -Fe precipitates is also the SDW state.
153 citations
TL;DR: In this paper, powder neutron diffraction data have been used to refine the crystal and magnetic structures of the ordered perovskites Sr2LuRuO6, Ba2YRuO6 and Ba2LuLuO6.
134 citations
TL;DR: On deduit les proprietes magnetiques d'un modele de Hubbard bidimensionnel des resultats de simulations Monte-Carlo.
Abstract: Magnetic properties of the two-dimensional Hubbard-model are inferred from results of Monte Carlo simulations. Lattice sizes up to 8\ifmmode\times\else\texttimes\fi{}8 and temperatures down to $T=\frac{t}{20}$ ($t=\mathrm{hopping}$) were studied. The half-filled system is found to exhibit antiferromagnetic long-range order for all values of the Coulomb repulsion $U$. The low-temperature magnetic properties are found to be well described by spin-wave theory with renormalized local moment and spin-wave velocity. Numerical evidence presented suggests that when doped the system loses the long-range order immediately away from half filling.
128 citations
TL;DR: In this article, the authors used neutron diffraction to show that superconductivity affects the magnetic order in the magnetic field and showed that the different superconducting states identified in previous bulk measurements can be associated with different behaviors of magnetic order parameter.
Abstract: We use neutron diffraction to show that superconductivity affects the magnetic order in ${\mathrm{UPt}}_{3}$. The different superconducting states identified in previous bulk measurements can be associated with different behaviors of the magnetic order parameter. The data suggest that the coupling between multicomponent superconducting and magnetic order parameters leads to the variety of superconducting phases of ${\mathrm{UPt}}_{3}$.
113 citations
112 citations
TL;DR: A planar magnetic structure (PMS) was found in the interplanetary magnetic field data obtained by Sakigake at 0.8-1.0 AU.
Abstract: A distinctive magnetic structure in which azimuthal and latitudinal angles of field vectors are closely related to each other has been found in the interplanetary magnetic field data obtained by Sakigake at 0.8-1.0 AU. In this structure, termed a planar magnetic structure (PMS), the magnetic field vectors are nearly parallel to a fixed plane. This plane includes the spiral direction but is inclined to the ecliptic plane from 30{degree} to 85{degree}. The field vectors take almost all directions parallel to this plane. The PMS consists of several segments in which field directions are almost constant, and the segments are separated by tangential discontinuities where directional changes of the field vector occur abruptly without showing any preferred polarization. The ion number density, the ion temperature, and the plasma {beta} tend to be higher in the PMS than in the surrounding plasma. The PMS events are clearly distinct from magnetic clouds both in the field configuration and in the plasma conditions. During the 25-month period from July 1985 to July 1987, eight PMS events with durations of several hours have been identified. The PMS events may be associated with newly emerging magnetic structure in the photosphere from which magnetic tongues are extendedmore » into interplanetary space.« less
101 citations
TL;DR: In this paper, the ternary carbide Nd2Fe17C0.5 adopts a magnetic structure in which the easy magnetization direction is perpendicular to the c-axis.
Abstract: Neutron diffraction measurements were made at 300 K and 4.2 K on a polycrystalline sample of the composition Nd2Fe17C0.5. The crystal structure of this ternary carbide is very similar to that of the parent compound Nd2Fe17(Th2Zn17-type, R3m), the carbon atoms partially filling up the empty 9(e) site. At 4.2 K, the compound Nd2Fe17C0.5 adopts a magnetic structure in which the easy magnetization direction is perpendicular to the c-axis.
98 citations
TL;DR: In this paper, the magnetic relaxation rate Λ was investigated via quasielastic neutron scattering of the Kondo lattice CeCu2Ge2, and it was shown that Λ(T) is characteristic of heavy-fermion systems with a high temperature square root dependence and a limiting low temperature value, yielding a Kondo temperatureTK≈10K.
Abstract: Elastic and inelastic neutron scattering studies of the Kondo lattice CeCu2Ge2 were performed. AtTN=4.1 K an incommensurate magnetic order develops with an ordering wave vectorq0=(0.28, 0.28, 0.54) and an ordered moment µs=0.74 µB. The crystalline electric field splits the 4f1-J-multiplet of the Ce ion into a ground state doublet and a quartet at 191 K. The wave function of the ground state yields an ordered moment of 1.54µB. Thus, due to the onset of the formation of a Kondo singlet the magnetic moment is considerably reduced. The magnetic relaxation rate Λ was investigated via quasielastic neutron scattering. The temperature dependence of Λ(T) is characteristic of heavy-fermion systems with a high temperature square root dependence and a limiting low temperature value, yielding a Kondo temperatureTK≈10K. The quasielastic component of the scattered neutron intensities persists down to the lowest temperatures, well belowTN. This quasielastic line is regarded as a characteristic feature of heavy-fermion systems and corresponds to the enhanced value of the linear term of the specific heat.
TL;DR: In this paper, the structure of CoSb2O6 was investigated by neutron diffraction and magnetic susceptibility techniques, and the structure was tetragonal, of the trirutile type, with space group P4 2 mnm, a = 4.6495(2) A, c = 9.2763(6)A, and with no structural change down to 10 K.
TL;DR: In this article, the results of X-ray scattering studies of the rare earth metals and related new results for superlattices and thin slabs were reviewed and discussed in the context of lattice modulations.
Abstract: We review the results of X-ray scattering studies of the rare earth metals and present related new results for superlattices and thin slabs. In rare earth crystals we have observed weak structural modulations which accompany the magnetic ordering. The wave length of this modulation can be derived from a spin-slip model in accordance with symmetry considerations. X-ray scattering of both the charge and magnetization density modulations allow for highly accurate determination of the magnetic wave vector. The physical basis of our discussion is given in the context of lattice modulations. The implications of these results for the understanding of magnetic structure of rare earth superlattices are also discussed in the light of recent neutron diffraction studies of holmium-yttrium superlattices. The effect of the finite size of the magnetic block in a superlattice is considered and it is shown that significantly different behavior than in bulk is expected. In particular it is found that for thin slabs the ferromagnetic phase has the lowest energy.
TL;DR: In the absence of a complete microscopic theory of the high-temperature copper-oxide superconductors, several phenomenological theoretical approaches are being used to describe the intragranular magnetic structure in the mixed state.
Abstract: In the absence of a complete microscopic theory of the high-temperature copper-oxide superconductors, several phenomenological theoretical approaches are being used to describe the intragranular magnetic structure in the mixed state. The purpose of this paper is to review these approaches and to point out where further developments are needed.
TL;DR: A neutron-powder-diffraction study has been carried out on Pr{sub 2}CuO{sub 4}, which has the {ital T}{prime}-type structure of the new high-{ital T},sub {ital c}} electron superconductors, and shows the crystal structure is essentially unchanged.
Abstract: A neutron-powder-diffraction study has been carried out on Pr{sub 2}CuO{sub 4}, which has the {ital T}{prime}-type structure of the new high-{ital T}{sub {ital c}} electron superconductors The compound orders antiferromagnetically at about 270 K The magnetic intensities at 15 K can be equally well accounted for by a collinear magnetic structure with orthorhombic symmetry or a noncollinear structure with tetragonal symmetry In both cases, Cu moments are coupled antiferromagnetically within the CuO{sub 2} layers, the ordered moment being 048{mu}{sub {ital B}} at 15 K Rietveld refinement at 298 and 15 K shows the crystal structure is essentially unchanged; in particular, there is no detectable distortion at low temperature
TL;DR: In this article, the superparamagnetic relaxation times for polycrystalline Fe 3 − x V x Al alloys with DO 3 -type structure and 0 x x, while the average magnetic moment of the iron atoms in the alloys decreases linearly with x.
Abstract: Polycrystalline Fe 3 − x V x Al alloys with DO 3 -type structure and 0 x x , while the average magnetic moment of the iron atoms in the alloys decreases linearly with x . The alloys with x > 0.5 do not exhibit any long-range magnetic order at temperatures above 4 K. High values of the magnetization and its markedly non-linear variation with the magnetic field intensity together with the absence of Zeeman splitting in the Mossbauer spectra suggest super-paramagnetic properties for these alloys. Mossbauer investigations show that the superparamagnetic relaxation times at room temperature are less than 10 −8 s and decrease with increasing x . Considered in conjunction with magnetostatic studies, this appears to indicate a reduction in size of magnetic clusters with increasing x .
TL;DR: In this article, the magnetic properties of YFe2 were investigated using the polarised neutron technique and the magnetic intensity on the (220) reflection proved that the yttrium site carries a magnetic moment antiparallel to that of the iron site.
Abstract: The magnetic properties of YFe2 were investigated using the polarised neutron technique. Flipping ratios were measured for the first five reflections of a powder. The magnetic intensity on the (220) reflection proved that the yttrium site carries a magnetic moment antiparallel to that of the iron site. The results were discussed with regard to different magnetic form factor curves to be used for yttrium. The best fit to the experimental data was achieved when assuming 80% spin and 20% orbital contribution, values of mu Y=(0.67+or-0.04) mu B and mu Fe=(1.77+or-0.08) mu B were found.
TL;DR: In this article, the Mossbauer spectra of 57 Fe in a single-crystal YbFe 2 O 4, an antiferromagnetic Ising spin system on a triangular lattice, were measured below the Neel temperature, T N.
Abstract: Mossbauer spectra of 57 Fe in a single-crystal YbFe 2 O 4 , an antiferromagnetic Ising spin system on a triangular lattice, were measured below the Neel temperature, T N . Outermost groups of absorption spectra, those due to Fe ions in a 3+-like state, were investigated extensively as a function of the external magnetic field during measurement ( H meas ) as well as that during cooling ( H cool ) of the specimen through T N . It is concluded that there are three kinds of Fe [3+] ions of equal number, the spins of two of which are parallel to each other and antiparallel to the other. The effective field at the nuclei of the majority Fe [3+] spin is increased by H meas . Formation of short-range ordering of Fe ions with different valences is suggested, though the details are not clear at present.
TL;DR: In this paper, it was shown that the low temperature57Fe Mossbauer spectra reveal a spatially inhomogeneous magnetic structure in FeNi-invar alloys.
Abstract: Thirty years of Mossbauer spectroscopy correspond roughly to twenty-five years of FeNi-invar research using this method. The first systematic study of hyperfine fields in FeNi alloys, in both bcc and fcc phases, appeared in 1963, the first spectra were published probably in 1964. A very important fact is that fcc iron is an antiferromagnet; however, this iron phase is unstable at low temperature. In 1963, the possibility of performing low-temperature Mossbauer spectroscopy experiments on fcc iron precipitates in copper was shown. We shall demonstrate that the low temperature57Fe Mossbauer spectra reveal a spatially inhomogeneous magnetic structure in FeNi-invar alloys. This structure corresponds to magnetic invar anomalies. From the viewpoint of basic research in magnetism, it was opportune to enhance these anomalies. One possible way to do this was the alloying of manganese into the invar matrix. In this contribution, we limited our examples to the study of the classical Fe0.65Ni0.35 and the new (Fe0.65Ni0.35)1−x
.Mn
x
alloys, and refer to the literature with respect to other transition metal systems with similar properties. We will show the goal of Mossbauer spectrometry investigating the spin structure in disordered alloy systems via the vector nature of the hyperfine fields. Additionally, the combination of Mossbauer spectrometry with global techniques, i.e. DC magnetization and AC susceptibility allowed us to study the changes in magnetic properties of our disordered 3d transition metal alloys from a nearly collinear ferromagnet (pure FeNi-invar) over the reentrant spin-glasses and “pure” concentrated spinglasses towards the antiferromagnetic behaviour by varying the manganese concentration in small steps.
TL;DR: In this paper, the magnetoelastic properties of the cubic rare earth rare earth intermetallic DyAg have been studied in the field of magneto-elastic coupling and quadrupolar interactions.
TL;DR: In this article, the spin and orbital moments of the Laves phase intermetallic compound UFe2 were measured using both polarised and unpolarized neutrons. But the results showed that the net moment at the U site is only 0.01 mu B.
Abstract: Studies using both polarised and unpolarised neutrons have been performed on single crystals of the Laves phase intermetallic compound UFe2. The authors describe studies of the twinning characteristics (two crystals with a common (1, 1, 1) axis) of the sample, a feature that is probably common in these cubic compounds. They then describe studies with polarised neutrons to determine the magnitude of the spin and orbital moments on the uranium site. In agreement with a recent theoretical prediction these two moments are found to be almost equal, but oppositely directed in real space. The net moment at the U site is only 0.01 mu B. The polarised neutron experiments also allow them to put an upper limit on any possible anisotropy in the magnetisation. High-field magnetisation experiments up to (20 T) on the same crystal as used in the neutron experiments allow them to determine the conduction-electron polarisation.
TL;DR: In this article, the authors performed neutron diffraction measurements on the compound UNiSn above and below its magnetic transition temperature, and the magnetic structure is FCC type 1 antiferromagnetism with a uranium moment of (1.42±0.03)μ B parallel to the [100] axis.
TL;DR: In this article, magnetic susceptibility and neutron diffraction investigations on polycrystalline samples of the green phase Y2BaCuO5 showed that copper moments order antiferromagnetically at about 28 K.
Abstract: Magnetic susceptibility and neutron diffraction investigations on polycrystalline samples of the green phase Y2BaCuO5 show that copper moments order antiferromagnetically at about 28 K. Two magnetic reflections have been observed at T = 2 K which can be indexed as 10½ and ½1½ reflections implying the existence of two independent wave vectors k1 = (00½) and k2 = (½0½). The copper magnetic moments are 0.87(2)μB and are oriented at an angle of 39° to the c-axis in the (a, c)-plane.
TL;DR: A brief review of different types of permanent magnet materials is given in this paper, followed by a more detailed description of the basic properties of rare earth compounds of the type R 2 Fe 14 B.
TL;DR: In this article, solid solutions of TlCo2-xNixSe2 with 0 ⩽ x 2 were prepared and characterized from X-ray diffraction patterns, and it was determined that these solutions adopt the ThCr2Si2 type tetragonal structure.
TL;DR: In this article, the Tb5Si3 compound was studied in the hexagonal Mn5Sb3-type structure and the temperature range was between 4 and 150 K. The analysis of the 4 K reflections, gave the best fit between observed and calculated intensities for a propagation vector k = [0, 0,0,0.46] and terbium magnetic moments for the two sites 7.1μB and 7.3μB respectively.
TL;DR: The magnetic properties of GdMn 2 Ge 2 with a layer structure have been studied by measuring magnetization of the single crystal in high magnetic fields up to 150 kOe.
TL;DR: In this article, the magnetic properties of hexagonal GdGa2 and GdCu5 compounds have been investigated by measurements on resistivity, susceptibility and magnetization, and the unusual magnetic properties and the behaviour of the low temperature resistivity seem to be related to the incommensurate magnetic structure in compounds without magnetocrystalline anisotropy.
Abstract: The magnetic properties of the hexagonal GdGa2 and GdCu5 compounds have been investigated by measurements on resistivity, susceptibility and magnetization. Their magnetic structure has also been studied by neutron diffraction at a very short wavelength where the absorption cross section of gadolinium is not too high. Below TN = 22K, the neutron diffraction pattern of GdGa2 can be interpreted with a cycloidal structure with the propagation vector Q = (0.39, 0.39, 0). Below TN = 26K, GdCu5 orders in an incommensurate triangular structure associated with a propagation vector Q = (13, 13, 0.223). The unusual magnetic properties and the behaviour of the low temperature resistivity seem to be related to the incommensurate magnetic structure in compounds without magnetocrystalline anisotropy.
TL;DR: In this paper, the nature of the low-temperature magnetic phase transition in cubic Laves-phase Ce(Fe1-xCox)2 compounds with x=0.15, 0.20 has been determined using powder neutron diffraction measurements.
Abstract: The nature of the low-temperature (T approximately=90 K) magnetic phase transition in cubic Laves-phase Ce(Fe1-xCox)2 compounds with x=0.15, 0.20 has been determined using powder neutron diffraction measurements. Below this temperature, ferromagnetism is replaced by an antiferromagnetic phase, which consists of (111)-type sheets with parallel spins and antiparallel coupling of spins between adjacent (111) sheets. The orientation of the magnetic moments could not be uniquely determined; however, they are oriented within a cone that is defined by sin2 phi =2/3 relative to the (111) sheets and includes the (Fe, Co) sublattice nearest-neighbour directions. No difference in magnitude between the (Fe, Co) sublattice moments of the two phases could be detected, nor was any significant magnetic moment detected at the Ce sites in either phase. High-resolution neutron diffraction measurements show that the application of large magnetic fields ( approximately=4T) in the antiferromagnetic phase restores ferromagnetism and removes the associated structural distortion.