Showing papers on "Antiferromagnetism published in 1993"
TL;DR: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure as mentioned in this paper.
Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.
995 citations
16 Mar 1993
TL;DR: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure as discussed by the authors.
Abstract: Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.
924 citations
TL;DR: In this paper, the S = 1 Heisenberg model was used to fit the magnetic susceptibility of Y 2 BaNiO 5 to the crystal structure of NiO 5 and the best fit for J/k ≈ −285 K (T max ≈ 410 K).
192 citations
TL;DR: In this paper, the normal and superconducting properties in impurity-doped YBa 2 (Cu 1- x M x ) 3 O 7 (M=Zn and Ni) have been investigated by 63 Cu NMR and NQR techniques.
Abstract: The normal and superconducting properties in impurity-doped YBa 2 (Cu 1- x M x ) 3 O 7 (M=Zn and Ni) have been investigated by 63 Cu NMR and NQR techniques. The nonmagnetic Zn-doping into the CuO 2 plane in YBa 2 Cu 3 O 7 (YBCO 7 ) causes a local collapse of antiferromagnetic (AF) spin correlation near Zn impurities and induces a gapless superconductivity with a finite density of states at the Fermi surface. On the other hand, in the case of Ni doping, there is no appreciable modification except for a small decrease of T c , although the Ni spins behave actually as local moments. The gapless feature in Zn-doped YBCO 7 is shown to be consistently interpreted within the framework of the d -wave model with gap zeros of lines at the Fermi surface as argued in heavy fermion superconductors. It is pointed out that the AF spin fluctuation-induced superconductivity is applicable to high- T c cuprates.
165 citations
TL;DR: Coplanar nematic, random three-state Potts, and Neel orderings for the Heisenberg kagome lattice antiferromagnet are investigated with Monte Carlo simulations coupled with state-of-the-art histogram methods for data analysis.
Abstract: Antiferromagnetic ordering on a kagome$iaa--- net is frustrated by the geometry of the lattice. The infinite number of classical ground states suggests that the system might not order at zero temperature, even for Heisenberg spins. However, high-temperature series expansions and earlier simulations indicate that this degeneracy is resolved by thermal fluctuations (i.e., order by disorder), suggesting a nine-sublattice coplanar N\'eel-like ordering of the spins. Coplanar nematic, random three-state Potts, and N\'eel orderings for the Heisenberg kagome$aa--- lattice antiferromagnet are investigated with Monte Carlo simulations coupled with state-of-the-art histogram methods for data analysis. We see strong evidence for thermal selection of long-range order with the spin correlations exhibiting algebraic decay, but the low-temperature phases are also seen to posses a chiral domain structure and very short-range chiral correlations. It is argued that the spin correlations are, surprisingly, rather insensitive to this lack of chiral order. Our results are consistent with T=0 being a critical point for this model system.
151 citations
TL;DR: It is deduced that the ground state has small but nonzero long range antiferromagnetic order, and the temperature dependence of the uniform susceptibility and the specific heat is determined.
Abstract: We have studied the spin-1/2 Heisenberg antiferromagnet on the triangular lattice by high temperature series expansions. From an analysis of the antiferromagnetic structure factor and correlation length, we deduce that the ground state has small but nonzero long range antiferromagnetic order. We also determine the temperature dependence of the uniform susceptibility and the specific heat.
131 citations
TL;DR: A thin film of EuSe was used as a funnel barrier between the normal metal Ag and superconducting Al to show tunneling characteristics and enhanced Zeeman spliffing of the Al quasiparficle states because of the exchange interaction at the Al-EuSe.
Abstract: A thin film of EuSe was used as a funnel barrier between the normal metal Ag and superconducting Al. Tunneling characteristics at 0.45 K showed the following: (1) the absence of exchange splitting of the EuSe conduction band in zero magnetic field, where EuSe is antiferromagnetic; (2) field-dependent spin polarization of the tunneling electrons as high as 97% at H≥1.2 T; (3) enhanced Zeeman spliffing of the Al quasiparficle states because of the exchange interaction at the Al-EuSe; (4) a decrease in tunnel resistance by as much as 75% in magnetic field ≥1.7 T
127 citations
TL;DR: LiNiO 2 is a member of the solid solution series Li x Ni 2-x O 2 and has been suggested as an experimental spin 12 triangular lattice antiferromagnet.
127 citations
TL;DR: A magnetic susceptibility which decreases with decreasing temperature is observed in all CuO 2 based superconductors with less than optimal doping and it is proposed that in La 2-x Sr x CuO 4 this is due to spin density wave ordering which is prevented by the low spatial dimensionality.
Abstract: A magnetic susceptibility which decreases with decreasing temperature is observed in all CuO 2 based superconductors with less than optimal doping. We propose that in La 2-x Sr x CuO 4 this is due to spin density wave ordering which is prevented by the low spatial dimensionality, while in YBa 2 Cu 3 O 6.6 it is due to the interplay between antiferromagnetic fluctuations within a plane and singlet pairing of electrons between nearest neighbor planes
125 citations
TL;DR: The results suggest a coexistence of two subsystems with more localized 5f statesresponsible for the magnetic properties and less localized states responsible for the superconducting properties, compatible with an order parameter of octagonal d-wave symmetry.
Abstract: We report measurements of the resistivity and the specific heat, performed as a function of temperature, magnetic field, and hydrostatic pressure on the antiferromagnetic (T N =14 K) heavy-fermion superconductor (T c ≃2 K) UPd 2 A 3 . Our results suggest a coexistence of two subsystems with more localized 5f states responsible for the magnetic properties and less localized states responsible for the superconducting properties. The latter are compatible with an order parameter of octagonal d-wave symmetry
108 citations
TL;DR: The Cu magnetic form factor has been extracted from magnetic Bragg peak intensities measured at 15 K, and it is shown to have the large anisotropy expected for a Cu 3d x2-y2 state.
Abstract: Both the static and dynamic properties of the antiferromagnetic state in YBa 2 Cu 3 O 6.15 have been reinvestigated by neutron scattering. The crystal studied exhibited a Neel temperature of 410±3 K, with a continuous transition below 15 K to a magnetic structure with a doubled unit cell along the c axis. The Cu magnetic form factor has been extracted from magnetic Bragg peak intensities measured at 15 K, and it is shown to have the large anisotropy expected for a Cu 3d x2-y2 state. The form-factor anisotropy can explain much of the Q dependence of the inelastic magnetic cross section that has been observed in superconducting YBa 2 Cu 3 O 6+x
TL;DR: In this article, the Monte Carlo simulations for the Ising spin tiangular lattice antiferromagnet were used to reproduce the observed successive transition in the case of the exchange parameters 4 J 3 <2 J 2 ∼ J 1 <0.
Abstract: Magnetic ordering in a rhombohedrally stacked triangular lattice antiferromagnet, CuFeO 2 was investigated on powder and single crystals by measurements of neutron diffraction, magnetic susceptibility, Mossbauer effect together with Monte Carlo simulations. CuFeO 2 was found to exhibit transitions at T N1 =16±0.5 K and T N2 =11±0.5 K. The low temperature phase has an orthorhombic magnetic unit cell with collinear moments along the c -axis, whereas the intermediate temperature phase is a partially disordered phase with a monoclinic magnetic unit cell where 1/5 of moments remain paramagnetic. The Monte Carlo simulations for the Ising spin tiangular lattice antiferromagnet can reproduce the observed successive transition in the case of the exchange parameters 4 J 3 <2 J 2 ∼ J 1 <0. This combination of exchange parameters gives an account for the stability of the collinear magnetic structure in CuFeO 2 .
TL;DR: In this article, the magnetic properties of the ThCr 2 Si 2 -type arsenides EuM 2 As 2 (M = Fe, Co, Ni, Pd) and the new compounds LnFeAs (Ln = La, Ce, Pr, Nd) with PbFCl-type structure were investigated and the Eu compounds exhibit antiferromagnetic ordering of the europium sublattices.
TL;DR: In this article, a two-dimensional double-layered triangular antiferromagnet LuFe 3+ Fe 2+ O 4 single crystal was studied and the temperature variations of intensity in magnetic scattering can be explained qualitatively by assuming unequal exchange interactions among three sublattice.
Abstract: Magnetization, neutron diffraction and Mossbauer measurements have been performed on a two dimensional (2D) double-layered triangular antiferromagnet LuFe 3+ Fe 2+ O 4 single crystal. Two magnetic rods (0, 1, l ) and (1/3, 1/3, l ) with broad widths across them reveal that 2D magnetic ordering is not of long range and no 3D one occurs down to 4.2 K in contrast to an ordinary magnetic system. Thermoremanent magnetization measurements suggest that the system consists of various size ferrimagnetic clusters. The characteristic profile of l -scan in (0, 1, l ) can be realized by taking account of correlation among clusters for intra double-layers and inter double-layers. The temperature variations of intensity in magnetic scattering can be explained qualitatively by assuming unequal exchange interactions among three sublattice.
TL;DR: In this article, spontaneous non-reciprocal rotation and circular dichroism in spin magnetoelectric Cr2O3 were observed below the antiferromagnetic transition temperature TN=307 K and their temperature behaviour roughly corresponds to that of the order parameter.
Abstract: The reflection of light from a medium with ordered spin structure characterized by the breakdown of time-reversal and parity symmetry is expected to be non-reciprocal even if the net magnetic moment of the medium equals zero. We report on the first experimental observation of spontaneous non-reciprocal rotation and circular dichroism in spin magnetoelectric Cr2O3. Non-reciprocal effects were observed below the antiferromagnetic transition temperature TN=307 K and their temperature behaviour roughly corresponds to that of the order parameter. Observed values of (1-4)*10-4 for the magnetoelectric susceptibility in the optical range are several orders of magnitude higher than predicted earlier. This increase of the susceptibility is presumably attributable to electronic dipole transitions in the optical range.
TL;DR: In this paper, the magnetic properties of 2-(5-pyrimidinyl)-4,4,5, 5,5- tetramethyl-4, 5-dihydro-1H-imidazol-1-oxyl (2) were characterized by X-ray diffraction.
Abstract: 2-(5-pyrimidinyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-3-oxoimidazol-1-oxyl (1) and 2-(5-pyrimidinyl)-4,4,5,5- tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl (2) have been prepared and structurally characterized by X-ray diffraction. While in the imino nitroxide 2 the molecules are arranged in pairs, in 1 the radicals are regularly stacked with the pyrimidyl planes being parallel. The magnetic behavior of the two compounds is strikingly different: in 2 intrapair antiferromagnetic interactions are fairly strong (J=-54 cm -1 , H= -2JS i S j ), and in 1 a moderate intrastack ferromagnetic coupling (+18 cm -1 ) is observed
TL;DR: The magnetic susceptibilities of La2Mg1−xZnxIrO6 (0 < x < 1), La2NiO6, BaLaFeO6 and BaLaCoO6 have been measured as a function of temperature and applied magnetic field.
TL;DR: The symmetric periodic Anderson model is studied in the limit of infinite spatial dimensions within an essentially exact quantum Monte Carlo method, where the single-particle spectral function develops a gap 4, and the neutron structure factor also developing a gap ≃2Δ.
Abstract: The symmetric periodic Anderson model is studied in the limit of infinite spatial dimensions within an essentially exact quantum Monte Carlo method. The single-particle spectral function develops a gap 4, and the neutron structure factor also develops a gap ≃2Δ. Depending upon the ratio of 4 to other energy scales, there is a transition to an antiferromagnetic state. In the paramagnetic state, both the f orbital specific heat and ferromagnetic susceptibility display rough scaling with T/Δ; for T>Δ they are heavy-fermion-like while for T<Δ they are insulatorlike
TL;DR: In this article, the origin of the pair-delocalized ground state of spin S = 2, observed in chemically symmetric mixed-valence [Fe 3 S 4 ] 0 cores present in proteins and synthetic models, was analyzed in the framework of an effective-Hamiltonian model, comprising terms for excess-electron transfer (leading to double-exchange coupling of the paramagnetic Fe(III) cores), vibronic coupling (trapping the excess electron), and antiferromagnetic exchange.
Abstract: The origin of the pair-delocalized ground state of spin S=2, observed in chemically symmetric mixed-valence [Fe 3 S 4 ] 0 cores present in proteins and synthetic models, is analyzed in the framework of an effective-Hamiltonian model, comprising terms for excess-electron transfer (leading to double-exchange coupling of the paramagnetic Fe(III) cores), vibronic coupling (trapping the excess electron), and antiferromagnetic exchange. The basic mechanisms underlying the inhomogeneous electron distributions in trinuclear mixed-valence clusters with paramagnetic ion cores are illustrated in a simple model with electronic structure d 1 -d 1 -d 2
TL;DR: In this paper, the authors investigated the magnetic and superconducting properties of the new heavy fermion superconductors (HFS), UNi 2 Al 3 and UPd 2Al 3, by means of 27 Al NMR and NQR.
Abstract: Both magnetic and superconducting characteristics of the new heavy fermion superconductors (HFS), UNi 2 Al 3 and UPd 2 Al 3 have been investigated extensively by means of 27 Al NMR and NQR. Systematic studies of the nuclear-spin-lattice relaxation time T 1 , the Knight shift and the spectrum of 27 Al have revealed different types of magnetic fluctuations and spin structure between these two compounds. UNi 2 Al 3 shows a band-type itinerant antiferromagnetic behavior, while UPd 2 Al 3 belongs to a heavy fermion antiferromagnet with an ordinary size of U-derived moment. In the superconducting state, the relaxation behavior in UPd 2 Al 3 is similar to those observed in the other HFS reported so far, providing an evidence for an unconventional anisotropic superconductivity with line of gap zeros on the Fermi surface as well. Knight shift has been found to decrease considerably below T c , showing that the pseudo spin is well defined, not affected by the impurity scattering.
TL;DR: In this paper, heat capacity, magnetization, and electrical resistivity measurements were carried out on a heavy-fermion system with an upper ordering temperature that is believed to be a transition from the paramagnetic state to a c-axis ferrimagnetic state, which in turn transforms a colinear antiferromagnetic (AF) state at 18 K.
Abstract: Heat capacity, magnetization, and electrical resistivity measurements were carried out on ${\mathrm{CeCoGe}}_{3}$ and ${\mathrm{LaCoGe}}_{3}$. ${\mathrm{CeCoGe}}_{3}$ was found to be a heavy-fermion system with \ensuremath{\gamma}=111 mJ/mole Ce ${\mathrm{K}}^{2}$. Two magnetic transitions were found at \ensuremath{\sim}21 and \ensuremath{\sim}18 K in the absence of a magnetic field. The upper ordering temperature is believed to be a transition from the paramagnetic state to a c-axis ferrimagnetic (FERRI) state, which in turn transforms a colinear antiferromagnetic (AF) state at \ensuremath{\sim}18 K. The AF phase undergoes an irreversible phase transition to the FERRI state under an applied magnetic field. Consequently, magnetic glasslike behaviors such as thermal and magnetic hysteresis, frozen moment, and magnetic relaxation were observed. A nonhysteretic metamagnetic transition to a c-axis ferromagnet (FERRO) was observed at high magnetic fields. The critical spin-flip field, ${\mathit{H}}_{\mathit{m}}$, increases in the FERRI state, and decreases in the AF state as temperature decreases. The magnetic data also suggest that the Ce moments in the ab plane are antiferromagnetically aligned in all three magnetic phases. The existence of both ferromagnetism and antiferromagnetism implies that there may be close competition of ferromagnetic and antiferromagnetic exchange interactions between Ce moments leading to possible spin frustration.
TL;DR: In this paper, the magnetic properties of several compounds of the type RMn 6 Ge 6 (R is a heavy rare-earth element) were determined and the magnetic behavior of these compounds was described as bootstrap ferrimagnetism.
TL;DR: In this paper, the ternary compounds YMn6Ge6 and LuMn 6Ge6 of the CoSn-B35-type structure (space group, P6/mmm) were studied and the results showed that at low temperature a spin reorientation process occurs in both compounds, yielding incommensurate antiferromagnetic arrangements.
TL;DR: Neutron diffraction measurements confirm the presence of long-range antiferromagnetic order in superlattices of cobalt oxide and nickel oxide and mean field analysis accounts for the layer thickness dependence of the ordering temperature.
Abstract: Neutron diffraction measurements confirm the presence of long-range antiferromagnetic order in superlattices of cobalt oxide and nickel oxide. A single transition temperature between the values for bulk CoO and NiO is evident for two samples with 36 A periods as previously reported, but the separate Ni and Co order parameters in a 72 A period superlattice approximate bulk behavior. In the latter sample the magnetic order remains coherent across ostensibly paramagnetic CoO interlayers above 400 K. Mean field analysis accounts for the layer thickness dependence of the ordering temperature
TL;DR: In this article, an essentially exact solution of the infinite dimensional Hubbard model is made possible by using a selfconsistent mapping of the Hubbard model in this limit to an effective single impurity Anderson model.
Abstract: An essentially exact solution of the infinite dimensional Hubbard model is made possible by using a self-consistent mapping of the Hubbard model in this limit to an effective single impurity Anderson model. Solving the latter with quantum Monte Carlo procedures enables us to obtain exact results for the one and two-particle properties of the infinite dimensional Hubbard model. In particular, we find antiferromagnetism and a pseudogap in the single-particle density of states for sufficiently large values of the intrasite Coulomb interaction at half filling. Both the antiferromagnetic phase and the insulating phase above the Neel temperature are found to be quickly suppressed on doping. The latter is replaced by a heavy electron metal with a quasiparticle mass strongly dependent on doping as soon asn<1. At half filling the antiferromagnetic phase boundary agrees surprisingly well in shape and order of magnitude with results for the three dimensional Hubbard model.
TL;DR: In this paper, the exchange coupling between a ferromagnetic film and an antiferromagnetic NiO film was investigated, and it was shown that the number of magnetic Fe and Ni atoms of (Ni81Fe19)100−xNbx and NiO, varied with the existence of nonmagnetic Nb at their interface.
Abstract: Exchange coupling between a ferromagnetic film and an antiferromagnetic NiO film was investigated. Bilayered ferromagnetic Ni81Fe19/antiferromagnetic NiO films had a large exchange coupling field and blocking temperature of about 200 °C. In trilayered Ni81Fe19/ferromagnetic (Ni81Fe19)100−xNbx/NiO films, a way could be developed to control the exchange coupling field at a small value by increasing the Nb of the intermediate film. The most important factor in the control seemed to be that the numbers of magnetic Fe and Ni atoms of (Ni81Fe19)100−xNbx, which contributed to the exchange coupling between (Ni81Fe19)100−xNbx and NiO, varied with the existence of nonmagnetic Nb at their interface. From experimental results with other trilayered Ni81Fe19/ferromagnetic (Ni100−xFex)93Nb7/NiO films, it was ascertained that the exchange coupling field seemed to be independent of the magnetic moment of the ferromagnetic film although unidirectional anisotropy constant was proportional to it. As for blocking temperature,...
TL;DR: In this article, measurements of the magnetization, specific heat, resistivity ρ, and magnetoresistivity of single-crystalline Czochralski samples are reported.
Abstract: We report on measurements of the magnetizationM, specific heatC, resistivity ρ, and magnetoresistivity of CeCu
6−x
Au
x
single crystals (x=0.3 and 0.5) grown by the Czochralski method. Antiferromagnetic ordering is observed inM andC for temperatures less thanT
N=0.48 K (x=0.3) and 0.95 K (x=0.5), similar to the ordering temperatures found previously for polycrystalline samples. As a function of magnetic fieldB, M(B) andC(T, B) are strongly anisotropic, with the easy axis along the crystallographicc direction (orthorhombic notation) as for pure CeCu
6
. For large magnetic fields where the magnetic ordering is suppressed, the specific heat can be described by the resonance-level model suggestive of a single-ion Kondo effect, similar to CeCu
6
where for largeB the short-range magnetic correlations are suppressed. The averaged Kondo temperature as determined from a number of properties decreases with increasingx, withT
K=4.0 K forx=0.3 and 3.0 K forx=0.5, compared to 5.8 K forx=0. The magnetoresistivity shows a negative contribution arising from incoherent Kondo scattering and a positive contribution associated with the magnetic order.
TL;DR: In this article, short-range antiferromagnetic (speromagnetic) behavior was observed for amorphous BiFeO3 by static magnetic measurements, ac susceptibility (χac) measurement, and 57Fe Mossbauer spectra measurements.
Abstract: Short‐range antiferromagnetic (speromagnetic) behavior was observed for amorphous BiFeO3 by static magnetic measurements, ac susceptibility (χac) measurement, and 57Fe Mossbauer spectra measurements. The magnetic behavior is classified into three temperature ranges: (i) paramagnet for T≳220 K; (ii) local clustering of spins for 20 K
TL;DR: In this article, the anisotropic kagome antiferromagnet is discussed as a possible candidate for glassiness in the absence of disorder, and numerical studies support the conjecture that this system is not a conventional magnetic system, and include a discussion of the relevant experimental system.
Abstract: The anisotropic kagome antiferromagnet is discussed as a possible candidate for glassiness in the absence of disorder. Numerical studies support the conjecture that this system is not a conventional magnetic system, and we include a discussion of the relevant experimental system SrCr 8-x Ga 4+x O 19