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Showing papers on "Antiferromagnetism published in 1996"


Journal ArticleDOI
TL;DR: In this paper, the magnetic susceptibility of α'-NaV 2 O 5 was measured in the temperature range from 2 K to 700 K and it was shown that below 34 K, the spin susceptibility rapidly decreases with decreasing temperature to a constant value of 1.49×10 -4 emu/V 4+ -mol.
Abstract: Stoichiometric powder samples of α'-NaV 2 O 5 were synthesized and the magnetic susceptibility was measured in the temperature range from 2 K to 700 K. The magnetic susceptibility has a good fit to the equation for an S =1/2 antiferromagnetic Heisenberg linear chain with J / k B =280 K and g =2 above 34 K. Below 34 K the magnetic susceptibility rapidly decreases with decreasing temperature to a constant value of 1.49×10 -4 emu/V 4+ -mol which is reasonable for spin-singlet V 4+ –V 4+ pairs. This rapid reduction of the spin susceptibility below 34 K suggests the existence of a spin-Peierls transition. α'-NaV 2 O 5 is a possible spin-Peierls compound with the highest critical temperature yet observed.

313 citations


Journal ArticleDOI
TL;DR: A detailed analysis of lattice effects on the magnetic behavior of the parent compound LaMnO3 by using the local-spin-density approximation (LSDA) and the Jahn-Teller distortion (JTD) is presented.
Abstract: The stability of the $A$-type antiferromagnetic order and canted magnetic structure of LaMn${\mathrm{O}}_{3}$ perovskite is explained in the itinerant-electron picture based on the local-spin-density approximation. We demonstrate the crucial role of the observed lattice distortion which strongly affects the magnetocrystalline anisotropy, as well as the anisotropic and isotropic exchange interactions in this compound.

264 citations


Journal ArticleDOI
TL;DR: In this article, LiMn2O4 and manganospinels belonging to the LiN 2O4-Mn4O9-LiMn5O12 system were prepared by solid-state reaction of various lithium salts and sources at temperatures ranging from 400 to 900°C and their exact stoichiometry was determined by X-ray diffraction, atomic absorption spectroscopy, and redox titration.

249 citations


Journal ArticleDOI
TL;DR: The dispersion of the spin waves propagating in the highest symmetry directions solving the problems related to twinning is measured and the whole spin wave spectrum is well accounted for.
Abstract: As part of a general work on doped manganese perovskites, we have carried out detailed neutron-scattering experiments on powder and single crystals of the othorhombic phase of undoped LaMn${\mathrm{O}}_{3}$. The temperature dependence of the sublattice magnetization has been determined in the antiferromagnetic phase (${T}_{N}=139.5$ K), and the critical exponent is $\ensuremath{\beta}=0.28$, well below that corresponding to a pure three-dimensional Heisenberg antiferromagnet. We have measured the dispersion of the spin waves propagating in the highest symmetry directions solving the problems related to twinning. The whole spin wave spectrum is well accounted for with a Heisenberg Hamiltonian and a single ion anisotropy term responsible for the easy magnetization direction (b axis). This term induces a gap of 2.7 meV at low temperature in the spin wave dispersion curve. An important result is that the ferromagnetic exchange integral (${J}_{1}\ensuremath{\approx}0.83$ meV), coupling the spins within the ferromagnetic basal plane (a,b), is larger by a factor 1.4 than the antiferromagnetic exchange integral (${J}_{2}\ensuremath{\approx}\ensuremath{-}0.58$ meV) coupling spins belonging to adjacent Mn${\mathrm{O}}_{2}$ planes along c.

239 citations


Journal ArticleDOI
TL;DR: In this paper, it is suggested that low-energy spin excitations are at the origin of these non-Fermi liquid (NFL) anomalies which occur at a zero-temperature quantum phase transition.
Abstract: In heavy-fermion systems with 4f or 5f atoms (such as Ce or U) the competition between the on-site moment compensation by the Kondo effect and the long-range RKKY interaction between localized magnetic moments leads to the possibility of either a non-magnetic or a magnetically ordered ground state. However, even in the case of no long-range magnetic order as exemplified by , short-range dynamic intersite correlations are observed. Yet, the thermodynamic and transport properties of this alloy at very low temperatures T resemble those of a Fermi liquid (FL). Upon alloying with Au, long-range incommensurate antiferromagnetism is observed in for x > 0.1. For x = 0.1 where , the specific heat C depends on T as , the magnetic susceptibility as , and the T-dependent part of the electrical resistivity as . This is in marked contrast to the FL behaviour . It is suggested that low-energy spin excitations are at the origin of these non-Fermi-liquid (NFL) anomalies which occur at a zero-temperature quantum phase transition. Large magnetic fields B restore FL behaviour. The low-T range of FL behaviour in C and extends towards higher T with increasing B, with the crossover temperature varying roughly linearly with B. Apart from changing the Au concentration x, the magnetic - non-magnetic transition can be tuned by applying pressure p to antiferromagnetic samples with x > 0.1. For x = 0.3, at and NFL behaviour is observed in the specific heat for this critical pressure. For x = 0.2, where we likewise observe a logarithmic divergence of C/T and for p = 6.9 kbar we recover FL behaviour. Finally, we report on a remarkable `universality' of C/T in the system with M = Au, Pd, Pt: regardless of how is reached in this system (alloying with different elements M, varying concentration, or applying pressure), the C/T versus ln T curves are practically identical. Possible origins of NFL behaviour are discussed.

217 citations


Journal ArticleDOI
TL;DR: In this paper, the static and dynamical properties of weakly coupled antiferromagnetic spin chains are treated using a mean-field approximation for the interchain coupling and exact results for the resulting effective one-dimensional problem.
Abstract: Static and dynamical properties of weakly coupled antiferromagnetic spin chains are treated using a mean-field approximation for the interchain coupling and exact results for the resulting effective one-dimensional problem. Results for staggered magnetization, N\'eel temperature, and spin wave excitations are in agreement with experiments on ${\mathrm{KCuF}}_{3}$. The existence of a narrow longitudinal mode is predicted. The results are in agreement with general scaling arguments, contrary to spin wave theory.

211 citations


Patent
18 Mar 1996
TL;DR: In this paper, a magnetic tunnel junction (MTJ) device is used as a magnetic field sensor or as a memory cell in a magnetic random access (MRAM) array.
Abstract: A magnetic tunnel junction (MTJ) device is usable as a magnetic field sensor or as a memory cell in a magnetic random access (MRAM) array. The MTJ device has a "pinned" ferromagnetic layer whose magnetization is oriented in the plane of the layer but is fixed so as to not be able to rotate in the presence of an applied magnetic field in the range of interest, a "free" ferromagnetic layer whose magnetization is able to be rotated in the plane of the layer relative to the fixed magnetization of the pinned ferromagnetic layer, and an insulating tunnel barrier layer located between and in contact with both ferromagnetic layers. The pinned ferromagnetic layer is pinned by interfacial exchange coupling with an adjacent antiferromagnetic layer. The amount of tunneling current that flows perpendicularly through the two ferromagnetic layers and the intermediate tunnel barrier layer depends on the relative magnetization directions of the two ferromagnetic layers. The ferromagnetic layers are formed in two separate spaced-apart planes that do not overlap in the region of the tunnel barrier layer, thereby eliminating any extraneous magnetic poles.

208 citations


Patent
27 Nov 1996
TL;DR: A magnetic tunnel junction device for use as a magnetic memory cell or a magnetic field sensor has one fixed ferromagnetic layer and one sensing magnetometer on opposite sides of the insulating tunnel barrier layer.
Abstract: A magnetic tunnel junction device for use as a magnetic memory cell or a magnetic field sensor has one fixed ferromagnetic layer and one sensing ferromagnetic layer formed on opposite sides of the insulating tunnel barrier layer, and a hard biasing ferromagnetic layer that is electrically insulated from but yet magnetostatically coupled with the sensing ferromagnetic layer. The magnetic tunnel junction in the device is formed on an electrical lead on a substrate and is made up of a stack of layers. The layers in the stack are an antiferromagnetic layer, a fixed ferromagnetic layer exchange biased with the antfferromagnetic layer so that its magnetic moment cannot rotate in the presence of an applied magnetic field, an insulating tunnel barrier layer in contact with the fixed ferromagnetic layer, and a sensing ferromagnetic layer in contact with the tunnel barrier layer and whose magnetic moment is free to rotate in the presence of an applied magnetic field. The stack is generally rectangularly shaped with parallel side edges. A layer of hard biasing ferromagnetic material is located near to but spaced from the side edges of the sensing ferromagnetic layer to longitudinally bias the magnetic moment of the sensing ferromagnetic layer in a preferred direction. A layer of electrically insulating material isolates the hard biasing material from the electrical lead and the sensing ferromagnetic layer so that sense current is not shunted to the hard biasing material but is allowed to flow perpendicularly through the layers in the stack.

180 citations


Journal ArticleDOI
TL;DR: The crossover from a magnetically ordered to a non-magnetic spin liquid state has been investigated in a series of resistance measurements under hydrostatic pressures of up to 30 kbar and at temperatures down to below 200 mK in the heavy fermion antiferromagnet CePd2Si2.
Abstract: The cross-over from a magneticallyordered to a non-magnetic spin liquid state has been investigated in a series of resistance measurements under hydrostatic pressures of up to 30 kbar and at temperatures down to below 200 mK in the heavy fermion antiferromagnet CePd2Si2. The electrical resistivity changes dramatically with increasing pressure. Near the critical pressure, at which the magnetic ordering temperature is extrapolated to zero, it exhibits a quasi-linear variation over two orders of magnitude in temperature. This non-Fermi liquid formof π(T) extends down to the onset of a new superconducting transition below 430 mK.

169 citations


Journal ArticleDOI
TL;DR: A theoretical possibility of disorder-induced antiferromagnetic long range order in spin-Peierls system has been presented in this article, which will be in accordance with the recent experimental indication of the coexistence of dimerization and Antiferromagnetism in CuGe 1- y Si y O 3.
Abstract: A theoretical possibility of the existence of disorder-induced antiferromagnetic long range order in spin-Peierls system has been presented, which will be in accordance with the recent experimental indication of the coexistence of dimerization and antiferromagnetism in CuGe 1- y Si y O 3 .

152 citations


Journal ArticleDOI
TL;DR: In this article, anisotropic magnetoresistance was used to measure the angle the magnetization makes relative to the easy direction, which gave energies larger by a factor of 2 than the traditional measurements of the shift in the hysteresis loop (an irreversible process) of the ferromagnetic layer in bilayer samples of Co/CoO.
Abstract: Direct ferromagnetic antiferromagnetic exchange biasing energy is determined by small reversible rotations of the magnetization away from the unidirectional easy axis using an externally applied magnetic field. The angle the magnetization makes relative to the easy direction is determined by measuring the anisotropic magnetoresistance. This technique gives energies larger by a factor of 2 than the traditional measurements of the shift in the hysteresis loop (an irreversible process) of the ferromagnetic layer in bilayer samples of Co/CoO. An apparent Co thickness variation of the experimentally determined exchange biasing interface energy indicates the Co magnetization is not uniform but probably spirals through the thickness of the film.

Journal ArticleDOI
TL;DR: In this article, a simplified model of polaron pairs was developed, whose central feature is competition between the usual, antiferromagnetic, virtual hopping interaction and the loss of carrier−magnetic ion exchange energy, by intermediate ions.
Abstract: The bound magnetic polaron (BMP) is the characteristic collective state of diluted magnetic semiconductors. Isolated BMP are well understood, but their interactions are only beginning to be explored. Recent polaron magnetization experiments on p‐ZnMnTe suggest a ferromagnetic polaron‐polaron interaction, in contrast to the invariably antiferromagnetic impurity exchange interaction in conventional semiconductors. To investigate this question theoretically, we have developed a simplified model of polaron pairs whose central feature is competition between the usual, antiferromagnetic, virtual‐hopping interaction, and the loss of carrier‐magnetic ion exchange energy, by intermediate ions, when the polaron moments are antiferromagnetically aligned. The model is sufficiently simple that its partition function can be calculated in detail. With reasonable parameters, it predicts a ferromagnetic polaron‐polaron interaction at low temperatures.

Journal ArticleDOI
TL;DR: In this article, the role of superexchange interaction among 3D and 4d orbitals of transition metal ions via oxygen ions was investigated and the 1:1 ordered perovskite type compounds Sr2MMoO6 (M = Mn.Fe.Co) were prepared and their structures and properties were examined.
Abstract: In order to investigate the role of superexchange interaction among 3d and 4d orbitals of transition metal ions via oxygen ions. 1:1 ordered perovskite-type compounds Sr2MMoO6 (M = Mn.Fe.Co) were prepared and their structures and properties were examined. Structural analysis using the powder X-ray diffraction data revealed that all of these compounds have a 1:1 ordered arrangement in their B-sites. Measurements of electrical resistivity and magnetic susceptibility revealed that these compounds have the valency pairs of Mn2+ (3d5:t2g3eg2), Mo6+ (4d0). Fe3+ (3d5:t2g3eg2), Mo5+ (4d1:t2g1) and Co2+ (3d7:t2g5eg2), Mo6+ (4d0). The properties of these compounds are summarized as follows: Sr2MnMoO6, semiconductive and antiferromagnetic: Sr2FeMoO6, metallic and ferrimagnetic: Sr2CoMoO6, semiconductive and antiferromagnetic.

Journal ArticleDOI
TL;DR: SrFeO3, an antiferromagnet with a relatively lowTN of 134 K, and Sr2FeCoO6, a ferromagnets with a highTC of 340 K, seem to represent the two electronic phases switched from one to the other, suggesting that the Co substitution tends to delocalize electrons of Fe parentage in a broadened σ* band.

Journal ArticleDOI
TL;DR: In this article, the ground state of a Heisenberg model with arbitrary spin S on a one-dimensional lattice composed of diamond-shaped units was examined, and it was shown that there exists a phase with four-spin cluster states, which was previously found numerically for a special value of S = 1/2.
Abstract: We examine the ground state of a Heisenberg model with arbitrary spin S on a one-dimensional lattice composed of diamond-shaped units. A unit includes two types of antiferromagnetic exchange interaction which frustrate each other. The system undergoes phase changes when the ratio between the exchange parameters varies. In some phases, strong frustration leads to larger local structures or clusters of spins than a dimer. We prove for arbitrary S that there exists a phase with four-spin cluster states, which was previously found numerically for a special value of in the S = 1/2 case. For S = 1/2 we show that there are three ground-state phases, and determine their boundaries.

Journal ArticleDOI
TL;DR: It is found that the x=0.5 compound is an antiferromagnetic insulator at room temperature.
Abstract: In this work we present a study of the magnetic and transport properties of the system LaNiO3-x (0≤x≤0.5) where the x=0 member is a well-known metallic oxide. We found that the x=0.5 compound is an antiferromagnetic insulator at room temperature. The metal-insulator transition is observed for an x value around x.25. The role played by the sample inhomogeneities on the occurrence of this transition is dis-cussed. © 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: The magnetism of the sesquilayer films is investigated by in situ Kerr effect measurements; the observed coercivity is explained by a novel domain wall pinning mechanism which is estimated to be 10 times stronger than the stress induced coercivity increase.
Abstract: The heteroepitaxy of Fe on W(110) is governed mainly by the large lattice mismatch f › 9.4% derived from the elemental lattice constants aW › 3.165 A and aFe › 2.866 A [1]. As a consequence of this mismatch only the first monolayer (ML) [2] iron grows pseudomorphically on W(110) at 300 K [3]. Misfit dislocations caused by the reduction of the strain energy of the Fe film are already created in islands of the second monolayer at a Fe coverage of about 1.5 pseudomorphic monolayers, as shown in a recent scanning tunneling microscopy (STM) study [4]. A central-force model [5] involving bulk iron elastic constants yields an elastic energy per surface atom of order 0.3 eV, which is a formidable contribution to any energy consideration regarding growth, structure, and magnetism of the iron film. Thus, stress induced effects are likely to affect the behavior of the film and will be discussed in this Letter. Not only the morphology of the film undergoes a transition from 1 to 2 ML thickness [4], but also four different magnetic regimes are of interest: (i) a submonolayer region, paramagnetic due to the absence of magnetic percolation [6], (ii) a ferromagnetic one monolayer region, characterized by a pronounced twofold in-plane anisotropy [7], (iii) an intermediate, “ sesquilayer” region, consisting of second layer islands on top of a one monolayer sea exhibiting, reportedly [8], antiferromagnetic order, and (iv) a 2 ML region without striking magnetic properties. The subject of this work is the investigation of the sesquilayer region at a coverage of 1.5 ML. We present for the first time stress measurements with submonolayer sensitivity taken during the growth of ultrathin iron films on W(110). The magnetism of the sesquilayer films is investigated by in situ Kerr effect measurements; the observed coercivity is explained by a novel domain wall pinning mechanism which is estimated to be 10 times stronger than the stress induced coercivity increase. The iron films were grown under ultrahigh vacuum (UHV) conditions on clean W(110) substrates at 300 K. Film and sample cleanliness were checked by Auger electron spectroscopy, the contamination level due to the only contaminants oxygen and carbon was found to be less than

Journal ArticleDOI
TL;DR: In this article, the temperature dependence of high-field susceptibility χ both parallel and perpendicular to the crystallographic c-axis, for a sample of well crystallized natural goethite (αFeOOH), was measured.
Abstract: We have measured thermoremanence (TRM) and the temperature dependence of high-field susceptibility χ both parallel and perpendicular to the crystallographic c-axis, for a sample of well crystallized natural goethite (αFeOOH). Susceptibility χ⟂ measured perpendicular to the c-axis was almost temperature independent between 50 and 300 K, while χ∥ measured parallel to the c-axis increased almost linearly with temperature over the same range. These are the dependences expected for an antiferromagnetic (AFM) substance with sublattice magnetizations along the c-axis. Extrapolation of the χ⟂ and χ∥ data trends to their point of intersection gives an estimate for the AFM Neel temperature TN of (120±2)°C. TRM's produced by cooling in a weak field applied either parallel or perpendicular to the c-axis had intensities of 2.4 × 10−4 Am²/kg and 1.2 × 10−5 Am²/kg, respectively. Since (MTRM)⟂ is only 5% of (MTRM)∥, the weak ferromagnetism of goethite must be parallel to the AFM spin axis, not perpendicular to it as in the case of hematite. The ferromagnetism is very hard: TRM was unaffected by AF demagnetization to 100 mT and by thermal demagnetization to 90°C. Above 90°C, TRM decreased sharply, reaching zero at (120±2)°C. Thus the ferromagnetic Curie point TC coincides with TN, as in hematite. However, the weak ferromagnetism cannot be due to spin canting, as it is in hematite, because canting of the sublattices would produce a net moment perpendicular to the c-axis, rather than parallel to the c-axis as observed.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of the layered materials Cu2(OH)3(n-CmH2m+1COO) (m = 0, 1, 7, 8, and 9) have been examined.
Abstract: Magnetic properties of the layered materials Cu2(OH)3(n-CmH2m+1COO) (m = 0, 1, 7, 8, and 9) have been examined. X-ray powder diffraction patterns indicate that the interlayer distance increases in the order of m. The interlayer distances of the m = 0 and 1 materials are shorter than the molecular heights of the intercalated carboxylates, respectively, while the distances of the m = 7−9 materials are nearly double those of the molecular heights of the corresponding carboxylates, indicating a bilayer structure in them. The temperature dependence of the paramagnetic susceptibilities of the m = 0 and 1 materials suggests an intralayer ferromagnetic interaction and an interlayer antiferromagnetic interaction. The metamagnetic behavior is supported by S-shape dependence of their magnetization curves. The temperature dependence of the paramagnetic susceptibilities of the m = 7−9 materials indicates an intralayer antiferromagnetic interaction, in opposition to those in the former two. Further, they show a diverge...

Journal ArticleDOI
TL;DR: The heavy-fermion compound CePdAl with ZrNiAl-type crystal structure (hexagonal space group) was investigated by powder neutron diffraction and the experimentally determined magnetic structure is in agreement with group theoretical symmetry analysis considerations, calculated by the program MODY, which confirm that for Ce(2) an ordered magnetic moment parallel to the magnetically easy c-axis is forbidden by symmetry as mentioned in this paper.
Abstract: The heavy-fermion compound CePdAl with ZrNiAl-type crystal structure (hexagonal space group ) was investigated by powder neutron diffraction. The triangular coordination symmetry of magnetic Ce atoms on site 3f gives rise to geometrical frustration. CePdAl orders below with an incommensurate antiferromagnetic propagation vector , and a longitudinal sine-wave (LSW) modulated spin arrangement. Magnetically ordered moments at Ce(1) and Ce(3) coexist with frustrated disordered moments at Ce(2). The experimentally determined magnetic structure is in agreement with group theoretical symmetry analysis considerations, calculated by the program MODY, which confirm that for Ce(2) an ordered magnetic moment parallel to the magnetically easy c-axis is forbidden by symmetry. Further low-temperature experiments give evidence for a second magnetic phase transition in CePdAl between 0.6 and 1.3 K. Magnetic structures of CePdAl are compared with those of the isostructural compound TbNiAl, where a non-zero ordered magnetic moment for the geometrically frustrated Tb(2) atoms is allowed by symmetry.

Journal ArticleDOI
TL;DR: Both perturbation results and bond-operator calculations show that this disordered ground state is an array of spin singlets spontaneously formed on four spin plaquettes that has lower energy than the columnar dimer state.
Abstract: We propose a new type of magnetically disordered ground state for a frustrated quantum antiferromagnet. This disordered state is an array of spin singlets spontaneously formed on four spin plaquettes. Both perturbation results and bond-operator calculations show that this phase has lower energy than the columnar dimer state. Analysis of available numerical data on finite clusters also supports the conclusion that this state is realized at intermediate frustrations.

Journal ArticleDOI
TL;DR: The crystal structure and magnetic properties of the molecular-based ferrimagnet N(n-C5H11)4MnIIFeIII(C2O4)3 have been determined as mentioned in this paper.
Abstract: The crystal structure and magnetic properties of the molecular-based ferrimagnet N(n-C5H11)4MnIIFeIII(C2O4)3 have been determined. The compound is orthorhombic, space group C2221, a= 9.707(3), b= 16.140(3), c= 19.883(7)A(120 K), Z= 4[R 0.047 for I > 2σ(I)]. The structure consists of hexagonal layers of alternating MnII and FeIII bridged by C2O42–, separated by layers containing only N(n-C5H11)4+ with the alkyl chains extended, though with the terminal bonds twisted towards the gauche conformation. The terminal CH3 are embedded in the hexagonal pockets formed by three C2O42–. Since both metal ions have 3d5 configuration with 6A1 ground states the magnetic properties in the paramagnetic region mimic those of a two-dimensional antiferromagnet. Below TN= 27 K an uncompensated moment estimated as 8.78 × 10–5µB atom–1 arises, the direction of which was identified as parallel to the c axis by single-crystal magnetization measurements.

Journal ArticleDOI
TL;DR: Inelastic neutron-scattering experiments have been performed on a single crystal of a compound with a spin fluctuation spectrum that is broad in energy and strongly correlated in wave vector, with maximum intensity at the Brillouin zone boundary as mentioned in this paper.
Abstract: Inelastic neutron-scattering experiments have been performed on a single crystal of $({\mathrm{Y}}_{0.97}{\mathrm{Sc}}_{0.03}){\mathrm{Mn}}_{2}$. The spin fluctuation spectrum is broad in energy and strongly correlated in wave vector, with maximum intensity at the Brillouin zone boundary. There is no magnetic scattering for Brillouin zones centered at the origin and at certain reciprocal lattice points, suggesting the existence of short-lived 4-site collective spin singlets. The unusual features of the dynamical susceptibility discovered in this experiment result from geometrical frustration and give new insight into the heavy-fermion-like behavior of the compound.

Journal ArticleDOI
TL;DR: Direct measurements of heat capacity from 80 to 540 K of antiferromagnetic superlattices of NiO, CoO, and MgO are used to study the effect of exchange coupling and layer thickness on magnetic ordering.
Abstract: Direct measurements of heat capacity from 80 to 540 K of antiferromagnetic superlattices of NiO (high Neel temperature TN ), CoO (low TN ), and MgO (nonmagnetic) are used to study the effect of exchange coupling and layer thickness on magnetic ordering. NiOyCoO superlattices with thin layers show a single heat capacity peak similar to a Ni0.5Co0.5O alloy; with increasing layer thickness, the peak splits into two maxima. Finite size effects are seen in uncoupled NiO and CoO. Observed shifts in TN show the importance of correlation lengths and spin fluctuations in the ordering. [S0031-9007(96)01343-9]

Journal ArticleDOI
26 Jan 1996-Science
TL;DR: In this article, a new class of magnetic behavior, random quantum spin chain paramagnetism, has been observed in the one-dimensional compound Sr 3 CuPt 1- x Ir x O 6.
Abstract: A new class of magnetic behavior, random quantum spin chain paramagnetism, has been observed in the one-dimensional compound Sr 3 CuPt 1- x Ir x O 6 . A random quantum spin chain system has S = spins coupled by Heisenberg exchange interactions that are randomly ferromagnetic or antiferromagnetic between neighbors along the chain. This condition was fulfilled by members of the solid solution Sr 3 CuPt 1- x Ir x O 6 ( x = 0, 0.25, 0.50, 0.75, and 1), whose end-members, Sr 3 CuPtO 6 and Sr 3 CuIrO 6 , are antiferromagnetic and ferromagnetic, respectively. Magnetic susceptibility data for the solid solution Sr 3 CuPt 1- x Ir x O 6 ( x = 0, 0.25, 0.50, 0.75, and 1) were collected and were found to be in excellent agreement with a theoretical model.

Journal ArticleDOI
18 Jul 1996-Nature
TL;DR: In this paper, the authors used small-angle neutron scattering to study the structure of the superconducting vortex lattice in ErNi2B2C and showed that the development of magnetic order causes the vortex lines to disorder and rotate away from the direction of the applied magnetic field.
Abstract: MAGNETISM and superconductivity are manifestations of two different ordered states into which metals can condense at low temperatures In general these states are mutually exclusive1; they do not coexist at the same place in a sample The study of the interplay between these properties has recently been revitalized by the discovery2,3 of a class of compounds with formula RNi2B2C (where R is a rare-earth element) which are both antiferromagnetic and superconducting at sufficiently low temperature4 It has been suggested5 that magnetic and superconducting order can coexist in these materials on an atomic scale Here we use small-angle neutron scattering to study the structure of the superconducting vortex lattice in ErNi2B2C Our results show that the development of magnetic order causes the vortex lines to disorder and rotate away from the direction of the applied magnetic field This coupling of superconductivity and magnetism provides clear evidence for microscopic coexistence of magnetic and superconducting order, and indicates that magnetic superconductors may exhibit a range of unusual phenomena not observed in conventional superconductors

Journal ArticleDOI
TL;DR: The periodic Hartree-Fock method has been adopted to calculate the ground-state spin-polarized wave function and total energy of rhombohedral Cr2O3 (corundum-type structure) as mentioned in this paper.

Journal ArticleDOI
TL;DR: The critical exponent β of the order parameter is 0.25 ± 0.01 as discussed by the authors, which is much smaller than values obtained for the three-dimensional Ising (0.326) and Heisenberg model.
Abstract: Neutron-scattering experiments have been performed on a LaMnO 3 single crystal. The spin waves exhibit two-dimensional anisotropic dispersion, that is, strong planar ferromagnetic coupling and weak antiferromagnetic interplane coupling with a finite gap. The critical exponent β of the order parameter is 0.25 ±0.01, which is much smaller than values obtained for the three-dimensional Ising (0.326) and Heisenberg (0.367) models. Ferromagnetic spin-wave-like dispersion remains for ω> 10 meV at T c ≈140 K, though the spectrum near the zone center is entirely overdamped around ω= 0.

Journal ArticleDOI
TL;DR: A field-induced insulator-metal (I-M) transition in Pr 0.7 Ca 0.3 MnO 3 has been studied with neutron diffraction experiments and it has been established that an applied field enforces a ferromagnetic spin alignment and drives Pr 1.0 T to a metallic state by actuating the double exchange mechanism and destroying the charge ordering.
Abstract: A field-induced insulator-metal (I-M) transition in Pr 0.7 Ca 0.3 MnO 3 has been studied with neutron diffraction experiments. Over the whole temperature range, the resistivity of Pr 0.7 Ca 0.3 MnO 3 shows insulating behavior at zero field, but exhibits an I-M transition at around 4.0 T at 5 K. It has been established that an applied field enforces a ferromagnetic spin alignment and drives Pr 0.7 Ca 0.3 MnO 3 to a metallic state by actuating the double exchange mechanism and destroying the charge ordering. This I-M transition at 5 K is accompanied with a large hysteresis. By contrast, in the field dependence at 50 K, antiferromagnetic and charge-order components are gradually recovered below 2.0 T in a field-decreasing process. Furthermore, a reentrant I-M-I transition has been observed in the temperature dependence at 2.5 T.

Journal ArticleDOI
TL;DR: In this paper, the structure of a synthetic sample of the mineral hydronium jarosite was determined by powder neutron diffraction, locating all the hydrogen atoms, but there was no evidence for long-range magnetic order in neutron powder diffraction patterns taken down to 1.5 K.
Abstract: We have determined the structure of a synthetic sample of the mineral hydronium jarosite by powder neutron diffraction, locating all the hydrogen atoms. Octahedrally coordinated Fe3+ ions are linked through their vertices to produce Kagome layers of moments with a coverage of ca. 95 ± 4%, depending on the synthesis conditions. Magnetic susceptibility measurements indicate strong coupling of these moments, with Curie–Weiss constant of –1200 K, but there is no evidence for long-range magnetic order in neutron powder diffraction patterns taken down to 1.5 K. Instead, we observe an anomaly in the magnetic susceptibility at 17.2 K which is a characteristic of spin-glass freezing and similar to experimental work and theory for other Kagome antiferromagnets.