Showing papers on "Magnetic anisotropy published in 1988"
IBM1
TL;DR: Strong, anisotropic magnetic relaxation of the field-cooled and zero-field--cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal is reported and interpreted with a thermally activated flux-creep model.
Abstract: We report strong, anisotropic magnetic relaxation of the field-cooled and zero-field-cooled magnetization along the principal axes of an Y-Ba-Cu-O single crystal and interpret it with a thermally activated flux-creep model. A simple scaling argument shows that high thermal activation causes magnetic irreversibilities and critical currents to drop below the threshold of detectability at a reduced temperature difference $1\ensuremath{-}t$ proportional to ${H}^{\frac{2}{3}}$, a power frequently observed in experiment and in particular in our crystal.
1,358 citations
TL;DR: In this paper, a cylindrically symmetric, constant alpha force-free magnetic field model was proposed to explain the types of variations of the magnetic field direction that are observed as a magnetic cloud moves past a spacecraft.
Abstract: Magnetic clouds observed at 1 AU are modeled as cylindrically symmetric, constant alpha force-free magnetic fields. The model satisfactorily explains the types of variations of the magnetic field direction that are observed as a magnetic cloud moves past a spacecraft in terms of the possible orientations of the axis of a magnetic cloud. The model also explains why the magnetic field strength is observed to be higher inside a magnetic cloud than near its boundaries. However, the model predicts that the magnetic field strength profile should be symmetric with respect to the axis of the magnetic cloud, whereas observations show that this is not generally the case.
665 citations
TL;DR: In this paper, the authors describe magnetization, resistivity, and x-ray diffraction data that consistently support sharper interfaces in Pd/Co thin-film layered structures (LS) than in Pt/Co LS.
Abstract: rf sputtered Pd/Co and Pt/Co thin‐film layered structures (LS) have perpendicular magnetic anisotropy, when the Co layer is ultrathin (<8 A in Pd/Co and <14 A in Pt/Co). The Co thickness (T) dependence of the anisotropy energy (Ku∼T) and the effective anisotropy field (HK∼1/T) in Pd/Co LS support an interfacial anisotropy as the source of the perpendicular magnetic easy axis. In contrast, the anisotropy is independent of Co thickness for thin Co layers in Pt/Co LS, and thus the mechanism for the perpendicular easy axis is thought to be different. We describe magnetization, resistivity, and x‐ray diffraction data that consistently support sharper interfaces in Pd/Co LS than in Pt/Co LS.
599 citations
TL;DR: Estimated tunneling rates of the magnetization in a single-domain particle through an energy barrier between easy directions prove to be large enough for observation of the effect with the use of existing experimental techniques.
Abstract: The probability of tunneling of the magnetization in a single-domain particle through an energy barrier between easy directions is calculated for several forms of magnetic anisotropy. Estimated tunneling rates prove to be large enough for observation of the effect with the use of existing experimental techniques.
420 citations
TL;DR: In this article, the magnetic anisotropy of Co ultrathin films sandwiched by Au was investigated and it was shown that the easy magnetization direction becomes perpendicular to the film plane for Co thicknesses lower than 11 A.
Abstract: We present experimental and theoretical investigations on the magnetic anisotropy of Co ultrathin films sandwiched by Au. Ferromagnetic resonance experiments revealed the presence of a large perpendicular surface anisotropy that makes the easy magnetization direction become perpendicular to the film plane for Co thicknesses lower than 11 A, as is observed in magnetization measurements. In order to explain this surface anisotropy, we propose various models, taking into account the imperfections of the films. For thicknesses below 11 A, there is a large increase of the coercive field with decreasing thickness. This effect is tentatively interpreted in a model of propagating Bloch walls, where the interfacial roughness plays an important role.
394 citations
TL;DR: In this paper, a new theory involving a random field at the interface which causes the antiferromagnet to break up into domains, whose size is inversely proportional to the exchange field offset is described.
Abstract: Exchange anisotropy refers to a group of phenomena which appear in ferromagnetic‐antiferromagnetic sandwiches, particularly to a field offset in the hysteresis loop. After a brief review of experiment and earlier theory, a new theory is described involving a random field at the interface which causes the antiferromagnet to break up into domains, whose size is inversely proportional to the exchange field offset. The theory is extended by considering the temperature dependence and also the topological properties of the domains, in particular nonzero winding numbers which increase the size of the domains and give them added stability. The metastability of such structures provides an explanation of the magnetic ‘‘training’’ effect observed in multiple cycles of the hysteresis loop.
378 citations
TL;DR: Co-Au multilayers with Co layer thicknesses between 22 and 5 \AA{}A, prepared by ion-beam sputtering, have an easy-plane magnetic anisotropy, which is attributed to a stronlgy enhanced interface anisotropic enhancement, due to sharpening of the interfaces as revealed by x-ray diffraction.
Abstract: Co-Au multilayers with Co layer thicknesses between 22 and 5 \AA{}A, prepared by ion-beam sputtering, have an easy-plane magnetic anisotropy Their saturation magnetization indicates the presence of diffuse interfaces, caused by ion-beam mixing Annealing of the multilayers at 250-300\ifmmode^\circ\else\textdegree\fi{}C leads to a perpendicular anisotropy for Co thicknesses below about 14 \AA{}A This effect is attributed to a stronlgy enhanced interface anisotropy, which is due to sharpening of the interfaces as revealed by x-ray diffraction
370 citations
TL;DR: In this article, a cubic discretization procedure of the micromagnetic energy functional is used to carry out numerical studies of the magnetization process in ferromagnetic cubes and their switching behavior is calculated for particle sizes in the range from 100 to 550 A.
Abstract: A cubic discretization procedure of the micromagnetic energy functional is used to carry out numerical studies of the magnetization process in ferromagnetic cubes. Equilibrium magnetization configurations and their switching behavior are calculated for particle sizes in the range from 100 to 550 A. In the model calculations the particles are assumed to have uniaxial crystalline anisotropy with an anisotropy constant of 18 500 erg/cm3, a saturation magnetization of 370 emu/cm3, and an exchange constant of 10−6 erg/cm. For particle sizes smaller than 520 A the remanent state has a flowerlike magnetization configuration. Beyond 520 A this state is replaced by a vortex structure about the easy axis. For particles smaller than 450 A switching occurs by approximately uniform rotation of the flower state. The switching fields are larger than the corresponding Stoner–Wohlfarth value. Beyond 450 A the application of an external field leads to the formation of a vortex configuration. The switching of the vortex con...
307 citations
TL;DR: In this article, it was shown that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro- or ferrimagnetic particles in rocks, in particular foliated rocks can actually be lineated.
Abstract: Magnetic susceptibility anisotropy is commonly used as a guide for determining stress and flow axes in rocks, and for assessing the suitability of anisotropic rocks for palaeomagnetic purposes. We have recently demonstrated however in laboratory produced samples that, as theoretically expected, susceptibility anisotropy is dependent on particle size. Multidomain particles of magnetite, or similar strongly magnetic particles with shape anisotropy, exhibit a maximum susceptibility parallel to their easy (remanent) magnetization axes whereas uniaxial single-domain particles exhibit a maximum susceptibility perpendicular to their easy magnetization axes. Hence susceptibility anisotropy does not yield an unambiguous determination of particle alignment in rocks independent of domain state. By demonstrating uniaxial single-domain anisotropy characteristics for the first time in a rock specimen, we show here that susceptibility measurements by themselves may not correctly identify the degree or type of alignment of ferro- or ferrimagnetic particles in rocks. In particular, apparently foliated rocks can actually be lineated (and vice-versa). Moreover rocks with low anisotropy of susceptibility can have a much higher anisotropy of remanence. Remanence anisotropy methods are shown to give unambiguous determinations of the degree and type of alignment.
274 citations
01 Jan 1988
TL;DR: Legvold et al. as discussed by the authors measured the basal plane magnetostrictions of Tb and Dy at low temperatures, which are 100 to 10000 times typical magnetostrains and still remain the largest known (~1%).
Abstract: By the early 1960’s, it was widely recognized that the rare earths possessed many extraordinary magnetic properties. Neutron diffraction measurements, for example, showed that the spin structures were much more complex than those of any of the classical ferromagnets or antiferromagnets. More importantly, in the heavy rare earth metals, the parallel coupling of large orbital and large spin angular momenta yielded huge magnetic moments of 9μ B and 10μ B, dwarfing the conventional values of 0.6 for Ni and 2.2 for Fe. Enormous magnetic anisotropies were also encountered in the heavy rare earth elements. In 1963, a breakthrough in magnetostrictive materials occurred with the measurement of the basal plane magnetostrictions of Tb and Dy at low temperatures (Legvold et al. 1963, Clark et al. 1963, 1965, Rhyne and Legvold 1965). These basal plane strains are 100 to 10000 times typical magnetostrictions and still remain today the largest known (~1%). Over wide temperature ranges, thermal expansions are dominated by the temperature dependences of the magnetostrains. Elastic moduli were found to be strongly influenced by the unprecedented magnetoelastic interactions. However, because of the low ordering temperatures of the rare earths the application of these magnetostrictive properties to devices operating at room temperature could not be achieved with the elements. Only Gd, which is essentially non-magnetostrictive, possesses a Curie point as high as room temperature.
240 citations
TL;DR: In this article, the magnetic and invar properties of RFe10T2 compounds have been studied and an analysis of the magnetocrystalline anisotropy in these materials is given.
Abstract: The structures and the magnetic properties of some novel ternary compounds were studied. These compounds have the approximate composition RFe10T2, where T represents Cr, V, Ti, Mo, W, or Si. The structure of all these compounds can be derived from the tetragonal ThMn12 structure type, but the crystallographic position occupied by the different T atoms is not the same. Most of the compounds have a homogeneity range represented by RFe12−xTx. This homogeneity range is fairly large in the case of T=V and strongly asymmetric for T=Ti and W. A structure determination is given for a representative member of the RFe10Si2 family. This structure determination is compared with results obtained previously for T=Mo and V, in which latter compounds the site occupancy of the T component is completely different from that in RFe10Si2. A survey is given of the magnetic and invar properties of RFe10T2 compounds. Special attention is paid to an analysis of the magnetocrystalline anisotropy in these materials.
TL;DR: Combined longitudinal and polar Kerr-effect measurements show that the anisotropy reverts to being in plane for films thicker than approx.
Abstract: The predicted perpendicular surface anisotropy is observed for ferromagnetic fcc Fe/Cu(100) via in situ polar Kerr-effect measurements. Square hysteresis loops are obtained for films 1.5 to 5.7 monolayers thick for 100-K growth. The region of stability of the perpendicularly magnetized state as a function of growth temperature and film thickness is delineated. Combined longitudinal and polar Kerr-effect measurements show that the anisotropy reverts to being in plane for films thicker than \ensuremath{\simeq}6 monolayers.
TL;DR: In this article, the magnetic properties of amorphous ferromagnets are well described within the random-anisotropy real-space model, which assumes that the neighboring spins are ferromagnetically coupled with each other, and that there is a local magnetic anisotropic whose axes are correlated over a small length Ra due to short-range structural order.
Abstract: Some magnetic properties of amorphous ferromagnets are well described within the random‐anisotropy real‐space model. This model assumes that the neighboring spins are ferromagnetically coupled with each other, and that there is a local magnetic anisotropy whose axes are correlated over a small length Ra due to short‐range structural order. The system is characterized by a small parameter λ∼R2aK/A which depends on temperature and on the concentration of magnetic atoms via the local anisotropy K and exchange constant A. In zero magnetic field the local magnetization smoothly rotates over the solid with a characteristic length Rf =Ra/λ2. The zero‐field susceptibility is very sensitive to the exchange, the anisotropy, and the amorphous structure: χ∝A3K−4R−6a. The magnetization law in approaching saturation (M→M0) is universal (M0−M)∝1/(H)1/2 for H<2A/M0R2a. These and other predictions of the model seem to be in a good agreement with many recent experimental results.
TL;DR: In this article, inelastic neutron scattering experiments performed on single crystals of the heavy fermion compounds CeRu2Si2 and CeCu6 were performed on both compounds.
TL;DR: In this paper, a simple model was proposed, where magnetization reversal is initiated in a volume equal to the activation volume and is determined by the formation of a domain wall, and magnetic viscosity measurements were obtained for ferrite and rare-earth transition-metal sintered magnets.
Abstract: Measurements of the temperature dependence of the coercive field, of the magnetic viscosity, and of the angular dependence of the coercive field are reported for ferrite and rare-earth-transition-metal sintered magnets. A satisfactory explanation for the observed properties is obtained in a simple model, considering that magnetization reversal is initiated in a volume equal to the activation volume and is determined by the formation of a domain wall. From magnetic viscosity measurements, the activation volume is found to be proportional to the cube of the domain wall width, delta . The observed angular dependence of the coercive field reveals that, in the activation volume, the anisotropy is much larger than the coercive field and is not strongly reduced with respect to the bulk. If the coercivity is determined by true nucleation in a fully saturated sample, this is unlike the usual assumption that the magnetocrystalline anisotropy is strongly reduced in the volume of the nucleus. >
TL;DR: In this article, the demagnetizing field and magnetostatic energy of a thin film with surface roughness has been calculated, and it has been shown that the roughness gives rise to an effective perpendicular anisotropy.
Abstract: The demagnetizing field and magnetostatic energy of a thin film with surface roughness has been calculated. It is shown that the surface roughness gives rise to an effective perpendicular anisotropy whose order of magnitude is evaluated as a function of the parameters characterizing the roughness. The results are discussed in connection with experimental situations.
TL;DR: Les mesures sont menees sur des superconducteurs d'oxyde de cuivre qui explicitent le regime experimental dans lequel les effets extrinseques sont negligeables and confirment l'existence of the tension intrinseque prevue.
Abstract: The torque on a superconductor in a magnetic field H has been thought to be dominated by trapped flux or sample shape effects, but it has recently been suggested that an anisotropic type-II material should experience an intrinsic torque for H(c1) much less than H, which in turn is less than H(c2). The predicted phenomenon results from transverse magnetization of the Abrikosov lattice. Measurements are presented on copper-oxide superconductors which delineate the experimental regime in which extrinsic effects are negligible and confirm the existence of the predicted intrinsic torque.
TL;DR: In this article, it is shown that if a proper interparticle separation is created in the film, the exchange-coupling effect can be reduced or eliminated, so the resulting film will have the low media noise and bit shift required for high performance drive applications.
Abstract: The application of thin-film media for Winchester-type rigid disk recording is considered The inherent close contact between the magnetic particles in the film introduces strong exchange coupling between them in addition to the magnetostatic interaction generally seen in the particulate-binder-type media The coupling causes the formulation of an intrinsic magnetic cluster that has a dimension much larger than the individual magnetic crystallites The exchange-coupling-induced magnetic cluster becomes the basic unit of magnetization reversal in the film under recording, and hence it is believed to cause noise and increase bit shift in the media It is shown that if a proper interparticle separation is created in the film, the exchange-coupling effect can be reduced or eliminated, so the resulting film will have the low media noise and bit shift required for high-performance-drive applications >
TL;DR: It is shown that a phase transition to ferromagnetism occurs always for arbitrarily small anisotropy, and renormalization-group scaling relations for the transition temperature and the temperature variation of the correlation length are obtained.
Abstract: We discuss the nature of ferromagnetism in ultrathin films of magnetic ions, here regarded as two-dimensional Heisenberg ferromagnets subject to uniaxial anisotropy with the easy axis normal to the film We show that a phase transition to ferromagnetism occurs always for arbitrarily small anisotropy Renormalization-group scaling relations for the transition temperature and the temperature variation of the correlation length are obtained Implications of these results are discussed
TL;DR: In this article, Neel's phenomenological model of magnetic surface anisotropy is generalized to hexagonal close-packed structures in order to determine the magnetic surface aisotropic properties of cobalt.
Abstract: Neel's phenomenological model of magnetic surface anisotropy is generalised to hexagonal close-packed structures in order to determine the magnetic surface anisotropy of cobalt. The results obtained are in fair agreement with experimental values for the Au(111)/Co interface. It is also shown that Neel's model allows the surface roughness to be easily taken into account.
TL;DR: In this paper, the authors investigated ternary compounds based on the tetragonal ThMn12 structure where M is Ti, Si, V, Cr, and Mo.
Abstract: Sm(Fe1−xMx)12 ternary compounds based on the tetragonal ThMn12 structure where M is Ti, Si, V, Cr, and Mo were investigated. M atoms have a preference for site occupation. Ti atoms occupy the 8i or 8j site and Cr atoms occupy the 8i site. Curie temperatures on Sm(M,Fe)12 compounds are around 590 K except for the SmMo2Fe10 compound (Tc=483 K). The SmTiFe11 and SmSi2Fe10 compounds have a high saturation magnetization and magnetic anisotropy.
TL;DR: In this article, the most remarkable characteristics of metallic glasses as well as their main technological applications are reviewed and the possibility of tailoring transition metal-metalloid amorphous alloys is analyzed and attention is also paid to the role and stability of properties such as a magnetostriction and magnetic anisotropy in connection with such applications.
Abstract: The most remarkable characteristics of metallic glasses as well as their main technological applications are reviewed. Particular interest is focused on stress transducers and magnetic field sensors. The possibility of tailoring transition-metal-metalloid amorphous alloys is analysed and attention is also paid to the role and stability of properties such as a magnetostriction and magnetic anisotropy in connection with such applications.
TL;DR: In this article, it was shown that the demagnetization factor for an ultrathin ferromagnetic film is thickness dependent and that the anisotropy resulting from the dipole-dipole interaction can be interpreted as a surface and a volume anisotropic which depend on the crystalline structure and orientation of the film.
Abstract: At the boundary of a ferromagnetic material, the local change in the surroundings of the atomic magnetic moments induces an additional magnetic anisotropy. The dipole‐dipole interaction, responsible for the form‐dependent demagnetizing field inside the ferromagnet, differs for magnetic moments at the boundary and magnetic moments inside the bulk material. By calculation it is shown that the demagnetization factor for an ultrathin ferromagnetic film is thickness dependent. However, the anisotropy resulting from the dipole‐dipole interaction can be interpreted as a surface and a volume anisotropy which depend on the crystalline structure and orientation of the film, but are independent of the thickness of the film.
TL;DR: In this paper, high-resolution neutron powder diffraction has been used to determine the crystal structures of YFe11Ti and YFe10Ti intermetallic compounds, and the temperature dependence of the magnetic anisotropy from 293 to 78 K was measured by the singular point detection technique.
TL;DR: In this paper, a new method for the determination of crystal field and exchange parameters in rare-earth/transition-metal compounds, involving the analysis of magnetisation curves, is described.
Abstract: A new method for the determination of crystal field and exchange parameters in rare-earth/transition-metal compounds, involving the analysis of magnetisation curves, is described Rather than trying to reproduce directly the magnetisation curves by computer diagonalisation using crystal field and exchange parameters, the method uses experimentally determined anisotropy constants These constants are parameters which reproduce the magnetisation curves but to which no special physical significance is attached The energy expansion in terms of these anisotropy constants allows one to avoid long iterative computing Application of this method to Nd2Fe14B results in an excellent description of the complex magnetic behavior of this compound
TL;DR: Magnetotransport measurements provide an ideal probe to determine the various anisotropy energies in epitaxial magnetic films as discussed by the authors, and both the EHE and the AMR have been used to study the magnetic properties.
Abstract: Magnetotransport measurements provide an ideal probe to determine the various anisotropy energies in epitaxial magnetic films. The extraordinary Hall effect (EHE) can be used to determine the perpendicular or surface anisotropy energy while the anisotropic magnetoresistance (AMR) can be used to investigate the in‐plane anisotropy energies. The advantage of magnetotransport over more tranditional measurement techniques used to determine these anisotropy energies is the ease of the technique, the lack of a need for sophisticated equipment, and the insensitivity of the techniques to the magnetic properties of a semiconducting or insulating substrate. Both the EHE and the AMR have been used to study the magnetic properties of epitaxial iron films grown on GaAs substrates. The results of the EHE and the AMR study and how the various anisotropy energies compare with those determined by the more traditional techniques of ferromagnetic resonance and vibrating sample magnetometry will be discussed.
TL;DR: In this article, the 155Gd Mossbauer effect and the magnetic properties were measured in the compounds GdCo4B, Gd3Co11B4, gd2Co7B3 and gdCo3B2 and it was shown that increasing B substitution entails an increase in the second-order crystal-field parameter, which explains the increase in magnetocrystalline anisotropy.
Abstract: The 155Gd Mossbauer effect and the magnetic properties were measured in the compounds GdCo4B, Gd3Co11B4, Gd2Co7B3 and GdCo3B2. The crystal structures of all these compounds are related and can be thought to be built up by an ordered substitution of B atoms into the Co sites in GdCo5. The observation of distinct types of quadrupole interactions at the various crystallographic nonequivalent Gd sites in these compounds allowed a semiempirical determination of a unique set of effective point charges which makes it possible to describe crystal-field effects in these materials in a satisfactory way. This set of semi-empirical point charges was successfully applied to analyse crystal-field effects in ternary rare-earth compounds of the type R2Fe14B and R2Co14B. In the RCo5-based materials it is shown that increasing B substitution entails an increase in the second-order crystal-field parameter, which explains the increase in magnetocrystalline anisotropy.
TL;DR: In this article, the angular dependence of coercivity in sintered magnets is analyzed within the framework of a model for magnetization reversal described previously, where the coercive field is much weaker than the anisotropy field, i.e. only the projection of the field along the magnetization is effective.
IBM1
TL;DR: Afin de faire une exploration complementaire de la phenomenologie de l'anisotropie d'echange, et dans le but d'obtenir des observations experimentales additionnelles qui pourraient aider a elucider la nature microscopique of l'interaction d'interface, on realise une etude de R.M.F.
Abstract: Ferromagnetic resonance (FMR) spectra of Permalloy thin films exchange-coupled to iron-manganese films are analyzed. Studies were made on bilayer, ferromagnetic-antiferromagnetic (FA) and trilayer (AFA) structures, as a function of both F and A layer thicknesses in the range 20--800 A\r{}. Data are presented at a frequency of 9.3 GHz for both in-plane and perpendicular directions of the applied field, and at 34.1 GHz, in-plane. Analysis of these data enables extraction of the magnetization, gyromagnetic ratio, and an exchange shift due to spin-wave stiffness and perpendicular-surface anisotropy, as a function of layer thickness. The azimuthal dependence of the in-plane resonance is used to determine the magnitude of the exchange anisotropy (bias field). The magnetization and gyromagnetic ratio show little dependence on the thickness of either the F or A layer down to 50 A\r{}, implying that the interfaces are sharp on a scale of a few lattice constants. Within this interfacial region the magnetization is reduced as a result of interaction with the antiferromagnet. We suggest that the perpendicular-surface anisotropy is created by exchange coupling to the antiferromagnet whose easy axes are not in the plane of the interface. Finally, we suggest a model for exchange anisotropy in which the antiferromagnetic domain pattern is not totally locked, but adjusts in response to the ferromagnetization. Such a model qualitatively explains the bias field exerted by the antiferromagnetic layer deposited before the ferromagnet, the field-training effect, the FMR linewidth, and the magnitude of the bias field.