Showing papers on "Ferromagnetism published in 1992"
TL;DR: The observed isotropic giant magnetoresistance (GMR) in nonmultilayer magnetic systems using granular magnetic solids is shown to occur in magnetically inhomogeneous media containing nonaligned ferromagnetic entities on a microscopic scale.
Abstract: We have observed isotropic giant magnetoresistance (GMR) in nonmultilayer magnetic systems using granular magnetic solids. We show that GMR occurs in magnetically inhomogeneous media containing nonaligned ferromagnetic entities on a microscopic scale. The GMR is determined by the orientations of the magnetization axes, the density, and the size of the ferromagnetic entities.
1,465 citations
TL;DR: The coexistence of remanent magnetization and unsaturated spins as well as the large negative magnetoresistance at low temperatures is explained by the formation of large bound magnetic polarons.
Abstract: Magnetotransport properties of p-type (In,Mn)As, a new diluted magnetic semiconductor based on a III-V semiconductor, are studied. The interaction between the holes and the Mn 3d spins is manifested in the anomalous Hall effect, which dominates the Hall resistivity from low temperature (0.4 K) to nearly room temperature, and in the formation of partial ferromagnetic order below 7.5 K, which is a cooperative phenomenon related to carrier localization. The coexistence of remanent magnetization and unsaturated spins as well as the large negative magnetoresistance at low temperatures is explained by the formation of large bound magnetic polarons.
964 citations
TL;DR: The synthesis of molecular-based ferromagnetic materials was investigated in this article, where special attention was given to the T{sub c} value and its relation to the stoichiometry and water content.
Abstract: The synthesis of molecular-based ferromagnetic materials was investigated. Special attention was given to the T{sub c} value and its relation to the stoichiometry and water content. 12 refs., 2 figs.
376 citations
TL;DR: The magnetic properties of Fe films epitaxially grown on Cu(100) have been correlated to their structure and morphology, and with the onset of dislocation formation, the films become magnetic in the bulk and the magnetization switches to in-plane orientation.
Abstract: The magnetic properties of Fe films epitaxially grown on Cu(100) have been correlated to their structure and morphology. Strained fcc iron films with thicknesses between 5 and 11 monolayers (ML) are ferromagnetically ordered at the surface with a perpendicular orientation of the magnetic moment, whereas the bulk of the films remains paramagnetic. The surface magnetism is related to an expanded interlayer distance at the surface. With the onset of dislocation formation at about 11 ML, the films become magnetic in the bulk and the magnetization switches to in-plane orientation.
330 citations
TL;DR: Magnetoresistive random-access memory (MRAM) is an integrated combination of nonvolatile thin film magnetic storage and semiconductor support circuits as mentioned in this paper, which can offer improvements of 100 in read time and substantial simplification in circuitry.
255 citations
TL;DR: Low-temperature magnetic properties of the p-nitrophenyl nitronyl nitroxide phases of p-NPNN were determined by measuring the specific heat, the magnetic susceptibility, and the hysteresis curve of magnetization above $^{3}\mathrm{He}$ temperature in external magnetic fields.
Abstract: Low-temperature magnetic properties of the \ensuremath{\beta} and \ensuremath{\gamma} phases of p-nitrophenyl nitronyl nitroxide (p-NPNN) were determined by measuring the specific heat, the magnetic susceptibility, and the hysteresis curve of magnetization above $^{3}\mathrm{He}$ temperature in external magnetic fields. The \ensuremath{\beta}-phase crystal undergoes a bulk ferromagnetic transition at 0.60 K, which was confirmed by the magnetic entropy of ln2 due to one unpaired electron on the radical molecule and the hysteresis curve. The \ensuremath{\gamma} phase, on the other hand, revealed an antiferromagnetic transition at 0.65 K and one-dimensional ferromagnetic fluctuations above it. The specific-heat data of the \ensuremath{\gamma} phase in external fields were analyzed by a mean-field theory incorporated in the one-dimensional Heisenberg model. The details of sample characterization of each phase based on thermal analysis are also given.
242 citations
IBM1
TL;DR: Experimental evidence is presented for the tunneling of polarized electrons from the apex of a ferromagnetic Ni tip into GaAs(110), which shows that highly polarized minority 3d electrons are preferentially extracted from the Fermi level of the tip.
Abstract: Experimental evidence is presented for the tunneling of polarized electrons from the apex of a ferromagnetic Ni tip into GaAs(110). The polarization is found to be negative and of highest magnitude at very low injection energies, which shows that highly polarized minority 3d electrons are preferentially extracted from the Fermi level of the tip.
206 citations
TL;DR: This method is tested here on the ferromagnetic metals Fe and Ni and the results for Fe agree very well with experimental data and the magneto-optical polar Kerr rotation is predicted accurately.
Abstract: We present a computational method for the ab initio study of magneto-optical quantities like the optical conductivity and the magneto-optical Kerr rotation based on density-functional theory. This method is tested here on the ferromagnetic metals Fe and Ni. The results for Fe agree very well with experimental data. The magneto-optical polar Kerr rotation is predicted accurately. For Ni the results are in fair agreement with experiment. In those points where deviations from experimental data are found, they can be traced back to the well-known fact that the local-density approximation is of moderate success in describing some of the Ni 3d bands.
198 citations
TL;DR: In this article, a shift hysteresis loop was used to investigate exchange anisotropy in 500 A CoxNi1−xO/300 A Ni81Fe19 polycrystalline bilayer couples.
Abstract: Shifted hysteresis loops were used to investigate exchange anisotropy in 500 A CoxNi1−xO/300 A Ni81Fe19 polycrystalline bilayer couples. Bilayers of Ni81Fe19 with NiO have a room‐temperature exchange field, He, of 30 Oe in the as‐deposited state. A maximum in the exchange field at room temperature was observed near x=0.4, indicating an optimal alloying of the properties of the high anisotropy CoO and the high Neel temperature NiO. The blocking temperatures of the exchange couples vary linearly with x, suggesting a linear dependence of the oxide Neel temperature with x.
192 citations
TL;DR: Ferromagnetism of 5d transition metal monolayers is predicted for the first time and a remarkable trend emerges: the element with the largest moment among the 3d, 4d, and 5d monolayer is shifted from Mn to Ru ( isoelectronic to Fe) and to Ir (isoelectronics to Co), respectively.
Abstract: Ferromagnetism of 5d transition metal monolayers is predicted for the first time. For Ir on Ag and Au(001) magnetic moments of 0.9${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ were found by ab initio alculations based on the full-potential linearized augmented-plane-wave method. Os is magnetic on Ag but nonmagnetic on Au. Comparing 5d magnetism with 4d and 3d results, a remarkable trend emerges: The element with the largest moment among the 3d, 4d, and 5d monolayers is shifted from Mn to Ru (isoelectronic to Fe) and to Ir (isoelectronic to Co), respectively. 4d and 5d magnetism is explained as a true-dimensional band-structure effect.
179 citations
TL;DR: In this article, structural features in mixed Mn3+, Mn4+ perovskites, Pr1−xAxMnO3 (A = Ca, Sr, Ba) are given.
TL;DR: The GMR is isotropic and is the consequence of the departure from ferromagnetic alignment of the Co particles, and the resistivity component responsible for GMR and its temperature dependence is determined.
Abstract: We report giant magnetoresistance (GMR) as much as 75% at 5 K and 24% at room temperature in granular Co-Ag. We show that the GMR is isotropic and is the consequence of the departure from ferromagnetic alignment of the Co particles. We have also determined the resistivity component responsible for GMR and its temperature dependence.
01 Jun 1992
TL;DR: In this paper, a comprehensive description of the slow dynamics of spin glasses and other complex systems is given, including random anisotropy and phase transitions in magnetic glasses, D.J. Sellmyer does ferromagnetism persist in the reentrant spin glass phase? I.S. Shapir.
Abstract: Random anisotropy and phase transitions in magnetic glasses, D.J. Sellmyer does ferromagnetism persist in the re-entrant spin glass phase?, I. Mirebeau towards a comprehensive description of the slow dynamics of spin glasses and other complex systems, E. Vincent magnetic anisotropy of spin glasses, J.S. Kouvel exchange frustration and transverse spin freezing, D.H. Ryan and M. Grant phase transitions in magnets with random uniaxial anisotropy, Y. Goldsmith the random field enigma, Y. Shapir.
TL;DR: Experimental evidence that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu (001) substrates is stabilized by in-plane magnetic anisotropies is presented.
Abstract: We present experimental evidence that ferromagnetic order at room temperature in ultrathin epitaxial Co(001) layers on Cu(001) substrates is stabilized by in-plane magnetic anisotropies. All relevant anisotropy contributions have been determined as a function of Co layer thickness with and without an additional Cu overlayer.
TL;DR: In this paper, U3Si∼5 has been thoroughly investigated with respect to crystal chemistry and magnetic properties; for most compounds, magnetic studies have been carried out at low temperatures for the first time (2 to 300 K, 0 to 5 T).
TL;DR: An orthogonality of magnetic orbitals results in the stabilization of a high spin state, that is, a propagation of a ferromagnetic interaction between magnetic centers as discussed by the authors, which can result in the formation of a magnetometer.
Abstract: An orthogonality of magnetic orbitals results in the stabilization of a high spin state, that is, a propagation of a ferromagnetic interaction between magnetic centers. Oxalato-bridged one-dimensional copper(II) complexes (Cu(en) 2 ] [Cu(ox) 2 ] (1) and [Cu(bpy)(ox)].2H 2 O (2) were designed for an each magnetic orbital on adjacent units to be orthogonal, which might result in a ferromagnetic intrachain interaction
TL;DR: In this paper, it was shown that magnetic exchange-coupling exists between Fe films separated by a non-metallic amorphous Si layer at 40 K and with increasing Si thickness the coupling oscillates from ferro-to antiferromagnetic and back to ferromagnetic with an approximate period of 16 A.
TL;DR: Stern-Gerlach measurements of aluminum, chromium, palladium, and vanadium clusters, none of which are ferromagnetic in the bulk, are described.
Abstract: Recent calculations have indicated the possibility of large permanent magnetic moments for clusters of nonferromagnetic materials. Here we describe Stern-Gerlach measurements of aluminum, chromium, palladium, and vanadium clusters, none of which are ferromagnetic in the bulk. No deflections were observed in any of these systems. Upper limits of the magnetic moments are reported.
IBM1
TL;DR: In this article, the metal-insulator transition in orthorhombic perovskites was accompanied by the sudden 3D magnetic ordering of the Ni ions (μNi ≈ 0.9 μB), described by a commensurate κ = (1/2, 0, 1/2) spin density wave.
Abstract: The metal-insulator transition in the orthorhombic perovskites PrNiO3 and NdNiO3 is accompanied by the sudden 3D magnetic ordering of the Ni ions (μNi ≈ 0.9 μB). The magnetic ground state, described by a commensurate κ = (1/2, 0, 1/2) spin density wave, is unprecedented in a perovskite structure. The coexistence of F and AF interactions suggests the existence of an orbital superlattice. This results from the breakdown of the degeneracy of the NiIII (t2g6 eg1) state due to electronic correlations. The gap is probably of charge-transfer type rather than originated by the exchange interactions.
TL;DR: In this paper, the authors found that the ferromagnetic coupling between electrodes of the junction strongly modified the domain structures and magnetization reversal processes in the area of tunnel junction, and that the hysteresis of tunneling resistance was closely connected with magnetization processes.
TL;DR: In this paper, the electronic and magnetic structure of fcc (γ-)Fe is determined using the local spin-density functional approximation and the ASW method to solve the band-structure problem self-consistently.
TL;DR: In this article, a spin split electron state was observed at the surface of a ferromagnet and three types of spin-split electron states appeared: the bulk magnetic bands, the surface states of Schottky type, and the image potential surface states.
Abstract: The development of surface science and specifically of spin-polarized electron spectroscopy has been the driving force for a new era of surface and 2D magnetism. Classical primary magnetic quantities such as the temperature dependence of the spontaneous magnetization, the Curie point, the magnetic anisotropies, the variation of the quantum mechanical exchange interaction at clean or modified surfaces, and special surface-induced magnetic structures can now be determined with spin-polarized electron spectroscopies. But a variety of new fields are also appearing, for instance ultrafast time-resolved magnetometry employing laser-induced photoemission of spin-polarized electrons, and imaging of magnetic domains with unprecedented spatial resolution via spin-polarized cascade electrons. Furthermore, by analysing the spin of the photoemitted electrons or by observing the Bremsstrahlung emitted when a spin-polarized electron beam strikes the surface, the majority- and minority-spin electron states in ferromagnets can be investigated separately. Three types of spin-split electron state appear at the surface of a ferromagnet: the bulk magnetic bands, the surface states of Schottky type, and the image potential surface states. With ultrathin ferromagnetic films, magnetometry employing the measurement of the spin polarization of low-energy cascade electrons produces magnificent images of the magnetic domains and reveals the conditions for their occurrence. The dramatic response of the spontaneous magnetization to external disturbances such as an applied magnetic field or an exchange field transferred from a substrate is also obtained. The critical phenomena observed in surface and 2D magnetism fit well into the framework set by the theory many years ago, while the theoretically predicted exotic 2D ferromagnetism in elements that do not exhibit magnetism in 3D has not yet been verified beyond doubt.
TL;DR: In this paper, the magnetic and electrical properties of U 7 Ge, U 5 Ge 3, U 3 Ge 4 and UGe 2 were clarified, measuring the electrical resistivity, thermoelectric power, Hall coefficient, magnetic susceptibility, magnetization and specific heat.
Abstract: We have clarified the magnetic and electrical properties of U 7 Ge, U 5 Ge 3 , U 3 Ge 4 and UGe 2 , measuring the electrical resistivity, thermoelectric power, Hall coefficient, magnetic susceptibility, magnetization and specific heat. U 7 Ge and U 5 Ge 3 , which are Pauli paramagnetic compounds, become superconductive below 1.40 K and 0.99 K, respectively. The latter compounds U 3 Ge 4 and UGe 2 indicate ferromagnetism. Anisotropic properties of UGe 2 are well reflected in the electrical resistivity, magnetic susceptibility and magnetization.
TL;DR: In this paper, the ferromagnetic properties of compaction-prepared nanocrystalline Ni specimens were investigated in order to study the correlation between the disordered interfacial structure and the macroscopic properties.
TL;DR: In this article, the structure and properties of the thermodynamically stable δ−phase Mn1−xGax single crystal thin films grown on GaAs were reported and the properties of these films were analyzed.
Abstract: We report the structure and properties of the thermodynamically stable δ‐phase Mn1−xGax single crystal thin films grown on GaAs. X‐ray Θ–2Θ scans and grazing‐incidence scattering measurements confirmed that the unit cell of this phase is tetragonal (a=0.279 nm, c=0.351 nm) and grows with the c‐axis oriented normal to the {001} GaAs substrate surface. X‐ray emission spectroscopy confirmed the composition to be 62±2% Mn. Polar Kerr rotation, SQUID and vibrating sample magnetometer measurements with the field applied along the thin‐film normal showed nearly perfect square hysteresis loops confirming perpendicular anisotropy of the films. The film exhibits a Kerr rotation angle of ∼0.1° at 820 nm, a coercivity of 6.27 kOe and a saturation magnetization of 460 emu/cm3. The optical reflectivity of the film was 65%–70% over a broad range of wavelengths. This unique set of properties make it a very promising material for magneto‐optic recording with the additional potential of integrating semiconductor/magnetic d...
TL;DR: In this article, a quantum-statistical theory of magneto-resistance properties of spin-valve sandwiches of the form: substrate |F1|Cu|F2|FeMn.
Abstract: Using Kubo formalism, we develop a quantum-statistical theory of the magneto-resistance properties of spin-valve sandwiches of the form: substrate |F1|Cu|F2|FeMn. F1 and F2 are ferromagnetic transition metals or their alloys, the magnetization of F2 is constrained by exchange anisotropy. The model is based on the coherent interplay between F1 and F2 of spin-dependent scattering phenomena occurring in the bulk of the ferromagnetic layers. We first study the case of F1|Cu|F2 sandwiches with specular reflexion on outer boundaries (which is equivalent to the case of infinite multilayers). Scattering at the substrate |F1 interface is then considered also taking into account the highly resistive FeMn layer. Within these conditions, we obtain good quantitative agreement with experimental data. The results of this quantum-theoretical interpretation are then compared to those obtained by a classical approach based on the Fuchs-Sondheimer theory.
TL;DR: Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone.
Abstract: Angle-resolved photoemission is used to determine the temperature-dependent electronic properties of ferromagnetic bulk Gd along Γ-A of the three-dimensional Brillouin zone. The Δ 2 band exchange splitting (0.85 eV) and dispersion (0.5 eV) are in reasonably good agreement with self-consistent local spin-density approximation calculations. The conduction-band magnetic exchange splitting vanishes at the Curie temperature following a conventional power law with a Heisenberg critical exponent
13 Apr 1992
TL;DR: In this paper, the effect of exchange interactions between the antiferromagnetic Co-oxide shell and the ferromagnetic co core on the magnetic behavior of the powders has been investigated.
Abstract: Fine particles of Co in the size range of 50-350 AA by the vapor deposition technique have been prepared. The dependence of magnetization on size and temperature has been studied. A maximum coercivity of 1500 Oe was obtained for a particle size of 350 AA. Magnetic and structural measurements indicate a shell-type structure with an FCC (face centered cubic) Co core surrounded by a Co-oxide shell. The effect of exchange interactions between the antiferromagnetic Co-oxide shell and the ferromagnetic Co core on the magnetic behavior of the powders has been investigated. The core/shell structure is responsible for the large coercivities present at cryogenic temperatures and the nonsaturation effects, which increase with decreasing particle size and with higher oxidation. The disappearance of the shift at 150 K marks the loss of exchange interaction between the Co-core and its CoO oxide coating. Thus the 150 K temperature could either be the blocking temperature or the Neel temperature of CoO crystallites present in the oxide shell. >
TL;DR: In this article, the curie-temperature and saturation magnetization of the metallic ferromagnetic perovskite La 2 3 Ba 1 3 MnO 3 decreases, when manganese is substituted by copper.
TL;DR: The magnetic ordering at the surface of epitaxial Cr overlayers on Fe(100) is studied by spin-polarized electron-energy-loss spectroscopy, proving directly that the surface Cr layer has a net ferromagnetic moment and that successive layers order antiferromagnetically.
Abstract: The magnetic ordering at the surface of epitaxial Cr overlayers on Fe(100) is studied by spin-polarized electron-energy-loss spectroscopy. The exchange asymmetry oscillates with the thickness of the Cr overlayer with a period of about two atomic layers, proving directly that the surface Cr layer has a net ferromagnetic moment and that successive layers order antiferromagnetically. The exchange asymmetry is predominantly due to spin-flip scattering. The spin-flip spectrum broadens toward lower energy with increasing thickness, suggesting that Cr may have a surface-enhanced magnetic moment