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Showing papers on "Ferromagnetism published in 1996"


Journal ArticleDOI
TL;DR: The relaxation processes of electrons and spins systems following the absorption of femtosecondoptical pulses in ferromagnetic nickel have been studied using optical and magneto-optical pump-probetechniques and the experimental results are adequately described by a model including three interacting reservoirs.
Abstract: The relaxation processes of electrons and spins systems following the absorption of femtosecond optical pulses in ferromagnetic nickel have been studied using optical and magneto-optical pump-probe techniques. The magnetization of the film drops rapidly during the first picosecond, but different electron and spin dynamics are observed for delays in the range 0--5 ps. The experimental results are adequately described by a model including three interacting reservoirs (electron, spin, and lattice).

1,920 citations


Journal ArticleDOI
16 Feb 1996-Science
TL;DR: In this article, the evolution of magnetic order from the microscopic to the macroscopic regime may be studied with the use of nanometer-scale clusters and a variety of new techniques can be employed to control the size of the magnetic clusters from the atomic level.
Abstract: The evolution of magnetic order from the microscopic to the macroscopic regime may be studied with the use of nanometer-scale clusters. A variety of new techniques can be employed to control the size of the magnetic clusters from the atomic level. Molecular beams are used to construct and measure the magnetic properties of isolated metallic clusters. Superparamagnetic metallic particles embedded in a metal exhibit dramatic field-dependent changes in electrical conduction, providing a measure of spin-dependent scattering. Related efforts in semiconductor hosts with the use of ion implantation have generated room-temperature ferromagnetic clusters that can be directly imaged by magnetic force microscopy.

434 citations


Journal ArticleDOI
TL;DR: In this paper, the magnetoresistance peak occurs around the Curie point, whereas for x = 0.5 the onset of magnetoreduction is somewhat below and increases monotonically as.
Abstract: Manganites of the series , with x = 0, 0.1, 0.3, 0.5, 0.7 and 1.0, have been characterized in ceramic form and thin films have been prepared by pulsed laser deposition. Characterization techniques included x-ray diffraction, conductivity and magnetoresistance, magnetization and susceptibility, optical spectroscopy and the Faraday effect. Both the films and ceramics exhibit a maximum low-temperature conductivity at which is coexistent with ferromagnetic order. The negative magnetoresistance effect is qualitatively different for the x = 0.3 and x = 0.5 compositions. For x = 0.3 the magnetoresistance peak occurs around the Curie point, whereas for x = 0.5 the onset of magnetoresistance is somewhat below and increases monotonically as . The applied field appears to modify the magnetic order (on the scale of the spin diffusion length) down to the lowest temperatures for x = 0.5, but for x = 0.3 the ferromagnetic order is essentially complete and collinear below the Curie point.

415 citations


Patent
23 May 1996
TL;DR: In this paper, the magnetoresistance effect element has two ferromagnetic layers, a non-magnetic layer provided between the two layers, and a layer containing an oxide or nitride as a principal component.
Abstract: There are provided a magnetoresistance effect element, a magnetic head, a magnetic head assembly and a magnetic recording system, which have high sensitivity and high reliability. The magnetoresistance effect element has two ferromagnetic layers, a non-magnetic layer provided between the ferromagnetic layers, and a layer containing an oxide or nitride as a principal component, wherein the layer containing the oxide or nitride as the principal component contains a magnetic transition metal element which does not bond to oxygen and nitrogen and which is at least one of Co, Fe and Ni.

389 citations


Journal ArticleDOI
TL;DR: In this article, a review of the strategies currently developed for the synthesis of molecular based magnetic materials is presented, focusing on the metal-radical approach, in which the materials are assembled using transition metal complexes and stable organic radicals as building blocks.
Abstract: The strategies currently developed for the synthesis of molecular based magnetic materials are reviewed. After a brief introduction resuming the conditions which are required to observe spontaneous magnetization, the organic, inorganic, organometallic approaches are illustrated. Particular attention is devoted to the metal-radical approach, in which the materials are assembled using transition metal complexes and stable organic radicals as building blocks.

385 citations


Journal ArticleDOI
14 Mar 1996-Nature
TL;DR: In this article, the Curie temperature demarcating the transition to the ferromagnetic state increases markedly with pressure until the magnetic order abruptly disappears at 6.8 kbar, indicating that magnetic coupling is very sensitive to intermolecular separation.
Abstract: Molecular solids that exhibit ferromagnetism are rare, and thus there is considerable interest in understanding the magnetic coupling mechanisms that operate in the few known examples(1). One such material is the charge-transfer salt NH4Ni(mnt)(2) . H2O, which consists of stacked planar metal ligands separated by ammonium cations. This salt is an insulator with localized spins that exhibit long-range ferromagnetic order at low temperatures (below 4.5 K)(2).3 Here we show that the Curie temperature demarcating the transition to the ferromagnetic state increases markedly with pressure until ferromagnetic order abruptly disappears at 6.8 kbar, indicating that the magnetic coupling is very sensitive to intermolecular separation. Using quantum-chemical calculations(3), we show that this pressure dependence arises from a competition between ferromagnetic coupling (resulting from nickel-sulphur intermolecular spin interactions), and antiferromagnetic coupling (from nickel-nickel interactions). We suggest that a similar interplay of spin-polarization effects might play a key role in determining the nature of the ground states (metallic, superconducting and so forth) observed in other molecular materials of this structural type(4,5).

366 citations


Journal ArticleDOI
TL;DR: In this article, the microstructural conditions required for high remanence and high coercivity isotropic permanent magnets were analyzed using a finite element technique, and an optimal microstructure consisting of small soft magnetic grains embedded between hard magnetic grains with a mean grain diameter of about D ≈ 20 nm was proposed.

257 citations


Journal ArticleDOI
TL;DR: J. F. Gregg,1 W. Allen,1 K. Ounadjela,2 M. Viret,3 M. Thompson,4 and J. M. Coey.
Abstract: By exploiting the simplicity of a novel transport measurement on a ferromagnetic striped domain structure in a thin film of cobalt, we report the first direct observation of ferromagnetic domain wall scattering and what we believe to be the first clear indication of giant magnetoresistive effects in a homogeneous magnetic system. $($The colossal MR effect, while seen in homogeneous materials, is believed to originate from a charge ordering phenomenon [see, for example, Y. Tokura et al., J. Appl. Phys. 79, 5288 (1996), and references therein], and is therefore distinct from GMR, which is an effect arising from spin dependent scattering. $)$ A new model is proposed to describe these observations which highlights the crucial role played by electron spin precession in determining the electrical transport properties of magnetic interfaces.

245 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


Journal ArticleDOI
TL;DR: In this article, an amorphous phase in Nd-Fe-Al system was formed in an extremely wide composition range of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning and the resulting reduced ratio of T x /T m was as high as 0.90 and the temperature interval between T x and T m is as small as 85 K.
Abstract: An amorphous phase in Nd-Fe-Al system was formed in an extremely wide composition range of 0 to 90 at% Fe and 0 to 93 at% Al by melt spinning. Based on the information on the amorphous formation, ferromagnetic Nd 90-x Fe x Al 10 bulk amorphous alloys with high coercive force at room temperature were obtained by a copper mold casting method. The maximum diameter of the cylindrical amorphous samples with a length of 50 mm is about 7 mm for the 20%Fe alloy and about 4 mm for the 30%Fe alloy. Neither glass transition nor supercooled liquid region is observed in the temperature range before crystallization, being different from previous bulk glassy alloys exhibiting a wide supercooled liquid region before crystallization. The onset temperature of crystallization (T x ) and melting temperature (T m ) are measured to be 778 and 863 K, respectively, for the Nd 70 Fe 20 Al 10 alloy. The resulting reduced ratio of T x /T m is as high as 0.90 and the temperature interval between T x and T m is as small as 85 K. The extremely high T x /T m and small ΔT m (=T m -T x ) values are the reason for the achievement of the large glass-forming ability. The bulk amorphous Nd 70 Fe 20 Al 10 alloy has a ferromagnetism with the Curie temperature (T c ) of about 600 K which is much higher than the highest T c (about 480 K) for the Nd-Fe binary amorphous alloy ribbons. The remanence (B,) and intrinsic coercive force ( i H c ) for the bulk Nd 60 Fe 30 Al 10 alloy are 0.122 T and 277 kA/m, respectively, in the as-cast state and 0.128 T and 277 kA/m, respectively, in the annealed state for 600 s at 600 K. The B r and 1 H c decrease to 0.045 T and 265 kA/m, respectively, for the crystallized Nd 60 Fe 30 Al 10 sample consisting of Nd+Al 2 Nd+δ phases and the maximum hard magnetic properties are achieved in the amorphous state. The hard magnetic properties for the bulk amorphous alloys are presumably due to the homogeneous development of ferromagnetic clusters with large random magnetic anisotropy. The finding of the bulk amorphous alloys exhibiting hard magnetic properties at room temperature is promising for the future development as a new type of metallic amorphous permanent magnet.

197 citations


Journal ArticleDOI
TL;DR: In this paper, the spin-wave spectra of two-dimensional composite materials consisting of periodic square arrays of parallel cylinders made of a ferromagnetic material embedded in a background was calculated.
Abstract: We calculate the spin-wave spectra of two-dimensional composite materials consisting of periodic square arrays of parallel cylinders made of a ferromagnetic material embedded in a ferromagnetic background. Each material is described by its spontaneous magnetization MS and exchange constant A. An external static magnetic field is applied along the direction of the cylinders and both ferromagnetic materials are assumed to be magnetized parallel to this magnetic field. We consider the spin-waves propagation in the plane perpendicular to the cylinders. We reveal the existence of gaps in the magnon band structure of composite systems such as the periodic array of Fe cylinders in an EuO matrix. We investigate the existence of these gaps in relation to the physical parameters of the materials involved. We also study the influence of the lattice parameter (i.e., the square array periodicity) and the effect of the filling fraction of the cylinders on the magnon band structure.

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.

Journal ArticleDOI
TL;DR: When metals are cooled, they often undergo a phase transition to a state exhibiting a new type of order as discussed by the authors, such as superconductivity and magnetization in zero-field magnetic fields.
Abstract: When metals are cooled, they often undergo a phase transition to a state exhibiting a new type of order. Metals such as iron and nickel become ferromagnetic below temperatures of several hundred degrees Celsius; electron spins order to produce a net magnetization in zero field. Other metals, such as lead and aluminum, become superconductors at cryogenic temperatures; electrons form Cooper pairs of opposite spin and momentum, leading to electrical conduction with zero resistance and to expulsion of magnetic fields.

Journal ArticleDOI
TL;DR: The magnetic properties of the nine title compounds were studied by magnetic susceptibility measurements with a SQUID magnetometer between 2 and 300 K as mentioned in this paper, with the exception of the cerium and samarium compounds showing Curie-Weiss behavior.

Patent
Stuart S. P. Parkin1
27 Nov 1996
TL;DR: In this article, a magnetic tunnel junction is made up of two ferromagnetic layers, one having its magnetic moment fixed and the other free to rotate, an insulating tunnel barrier layer between the two layers for permitting tunneling current perpendicularly through the layers, and a nonferromagnetic layer located at the interface between the tunnel barrier and one of the layers.
Abstract: A magnetic tunnel junction device, usable as a memory cell or an external magnetic field sensor, has a tunneling magnetoresistance response, as a function of applied magnetic field, that is substantially symmetric about zero field. The magnetic tunnel junction is made up of two ferromagnetic layers, one of which has its magnetic moment fixed and the other of which has its magnetic moment free to rotate, an insulating tunnel barrier layer between the ferromagnetic layers for permitting tunneling current perpendicularly through the layers, and a nonferromagnetic layer located at the interface between the tunnel barrier layer and one of the ferromagnetic layers. The nonferromagnetic layer increases the spacing between the tunnel barrier layer and the ferromagnetic layer at the interface and thus reduces the magnetic coupling between the fixed and free ferromagnetic layers, which has been determined to be the cause of unsymmetric tunneling magnetoresistance response about zero field. Even though the nonferromagnetic interface layer presents nonspin-polarized electronic states at the tunnel barrier layer interface, it unexpectedly does not cause a suppression of the tunneling magnetoresistance.

Journal ArticleDOI
TL;DR: In this article, the magnetic properties of γ-Fe2O3 nanoparticles synthesized by vaporization condensation in a solar image furnace have been studied using both magnetic measurements and Mossbauer spectroscopy.
Abstract: The magnetic properties of γ‐Fe2O3 nanoparticles synthesized by vaporization condensation in a solar image furnace have been studied using both magnetic measurements and Mossbauer spectroscopy. The mean size of the particles turns out to be easily controlled by changing the pressure conditions in the growth chamber. The particles exhibit superparamagnetic behavior at room temperature. Magnetic measurements show the appearance of magnetic hysteresis in the low‐temperature range and from the evolution with temperature of the ferromagnetic ratio, MR/MS, we have determined the distribution of the blocking temperatures for the smallest particles that is fitted to a log‐normal distribution leading to a mean blocking temperature 〈TB〉=38±15 K. The size distribution of the magnetic unit is also determined from this fitting, as well as from the Mossbauer spectra, obtaining a mean particle volume of about 3.5×105 A3.

Journal ArticleDOI
TL;DR: Inelastic neutron scattering is used to measure the spin wave dispersion throughout the Brillouin zone of the double-exchange ferromagnet La0.7Pb0.3MnO3 and yields unusual broadening of the high frequency spin waves, even within the ferromagnetic phase.
Abstract: We use inelastic neutron scattering to measure the spin wave dispersion throughout the Brillouin zone of the double-exchange ferromagnet La0.7Pb0.3MnO3. Magnons with energies as high as 95 meV are directly observed and an unexpectedly simple Heisenberg Hamiltonian, with solely a nearest-neighbor coupling of 8.79 +/- 0.21 meV, accounts for the entire dispersion relation. The calculated Curie temperature for this local moment Hamiltonian overestimates the measured Curie point (355 K) by only 15%. Raising temperature yields unusual broadening of the high frequency spin waves, even within the ferromagnetic phase.

Journal ArticleDOI
TL;DR: It is proposed that the approximately 3:1 ratio between MnIIIand MnIVatoms in LaMnO3.15 gives rise to a frustrated system with largely spin glass behaviour.

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 paper, density functional calculations are used to elucidate the electronic and magnetic structure of SrRuO3, and itinerant ferromagnetic behavior is found both in the cubic perovskite and the actual orthorhombic structure.
Abstract: Density functional calculations are used to elucidate the electronic and magnetic structure of SrRuO3. Itinerant ferromagnetic behavior is found both in the cubic perovskite and the actual orthorhombic structure. The calculated moment is 1.59 μB. Unusually strong hybridization is evident in both the electronic structure and magnetism. The Fermi velocities indicate significant spin differentiation of the transport properties.

Journal ArticleDOI
TL;DR: An intra-atomic noncollinear magnetization density has been calculated for the case of ferromagnetic fcc Pu, by means of a newly implemented general-local-spin-density-approximation method which treats the magnetizationdensity as a continuous vector quantity.
Abstract: An intra-atomic noncollinear magnetization density has been calculated for the case of ferromagnetic fcc Pu, by means of a newly implemented general-local-spin-density-approximation method which treats the magnetization density as a continuous vector quantity. The presence of noncollinearity is a general effect, not specific to Pu, which is shown to rise due to the interplay of the local exchange and the spin-orbit coupling. The form of the noncollinear part of the magnetization density is very sensitive to the space group symmetry as is demonstrated by calculations with the average spin moment along [001] and [111], respectively.

Journal ArticleDOI
TL;DR: In this article, a spin-fluctuation theory where the modes are coupled by interatomic exchange interactions is employed for the finite-temperature properties of ferromagnetic Fe, Co, and Ni.
Abstract: Finite-temperature properties are modeled for the itinerant-electron ferromagnets Fe, Co, and Ni by employing a spin-fluctuation theory where the modes are coupled by interatomic exchange interactions. Our method is based on the density functional theory using the local density approximation. The latter yields all parameters derived from constrained ground-state properties of noncollinear spin configurations to calculate ab initio the Curie temperatures, the magnetic susceptibilities, and, furthermore, the hcp-fcc phase transition of Co. Our results are in fair agreement with experimental data.

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: To reveal the relations between intergrain interactions, microstructure and magnetic properties like remanence and coercive field, the demagnetization curves for different three-dimensional grain structures are calculated as a function of the mean grain diameter.
Abstract: Micromagnetic calculations using the finite-element method provide a quantitative understanding of demagnetization processes in nanocrystalline ferromagnetic materials. In these materials demagnetization processes are mainly determined by short-range exchange and long-range dipolar interactions, which sensitively depend on microstructural properties. To reveal the relations between intergrain interactions, microstructure and magnetic properties like remanence and coercive field, we calculated the demagnetization curves for different three-dimensional grain structures as a function of the mean grain diameter: Starting from a single sphere, we successively constructed regular grain structures with increasing number of grains. The most complex grain arrangement consists of an ensemble of 35 isotropically distributed grains with disturbed surfaces. \textcopyright{} 1996 The American Physical Society.

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: 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 paper, large exchange bias effects (ΔE∼1.1 erg/cm2) were observed in antiferromagnetic (FeF2) and ferromagnetic bilayers grown on MgO.
Abstract: Large exchange bias effects (ΔE∼1.1 erg/cm2) were observed in antiferromagnetic (FeF2)–ferromagnetic (Fe) bilayers grown on MgO. The FeF2 grows along the spin‐compensated (110) direction. The FeF2–Fe interface roughness was characterized using specular and diffuse x‐ray diffraction and atomic force microscopy. The magnitude of the exchange bias field HE increases as the interface roughness decreases. These results imply that magnetic domain creation in the antiferromagnet plays an important role.

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: Substitution of Na, K, Rb, and Sr for La in the perovskite type structure complex oxide LaMnO 3 were carried out and their structure and properties were investigated.