Showing papers on "Single domain published in 1991"
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TL;DR: In this paper, it was suggested that in many ferromagnetic materials there may occur particles distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible.
Abstract: It is suggested that in many ferromagnetic materials there may occur particles distinct in magnetic character from the general matrix, and below the critical size, depending on shape, for which domain boundary formation is energetically possible. For such single-domain particles, change of magnetization can take place only by rotation of the magnetization vector. As the field changes continuously, the resolved magnetization may change discontinuously at critical values of the field. The character of the magnetization curves depends on the degree of magnetic anisotropy of the particle and on the orientation of easy axes with respect to the field. The magnetic anisotropy may arise from the shape of the particle, from magnetocrystalline effects, and from strain. A detailed quantitative treatment is given of the effect of shape anisotropy when the particles have the form of ellipsoids of revolution, along with a less detailed treatment for the general ellipsoidal form.
1,401 citations
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TL;DR: In this article, the authors show that the pseudo-single-domain properties of submicron magnetites are a result of coexisting multidomain and single-domain-like remanences.
Abstract: It has long been hypothesized that the pseudo-single-domain properties of submicron magnetites are a result of coexisting multidomain and single-domain-like remanences. We have separated these two types of remanence by low-temperature demagnetization (LTD), in which samples are cooled through the low-temperature magnetite isotropic point and rewarmed to room temperature, all in zero field. At the isotropic point, the first crystalline anisotropy constant vanishes, and multidomain remanence due to displaced domain walls will be unpinned. We measured stepwise alternating field (AF) and thermal demagnetization curves of weak-field thermoremanent magnetization (TRM) and anhysteretic remanent magnetization and of saturation isothermal remanent magnetization (IRMs), both with and without prior LTD, for magnetites with mean particle sizes of 215, 390, and 540 nm. The memory fraction of remanence recovered after LTD, which represents the single-domain-like component, decreased from 44% for 215-nm grains to 23% for 540-nm grains in the case of IRMs. Memory of TRM was approximately twice as large. AF decay curves were soft and multidomain-like before LTD but became harder and single-domain-like in shape after LTD. LTD removed most low unblocking temperature TRM and IRMs. Distributed low unblocking temperatures are therefore a multidomain phenomenon, probably resulting from successive adjustments of domain walls to changing internal fields and pinning strengths during heating.
96 citations
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TL;DR: Magnetization distributions in a rectangular permalloy particle with an 8:1 aspect ratio are presented in this article, where a magnetic field is applied along the easy axis of the particle, there is considerable change in the vortex pattern as the applied field varies, but the moment is nearly constant.
Abstract: Magnetization distributions in a rectangular permalloy particle with an 8:1 aspect ratio are presented. When a magnetic field is applied along the easy axis of the particle, there is considerable change in the vortex pattern as the applied field varies, but the moment is nearly constant. Magnetization reversal is sudden. When a field is applied oblique to the easy axis the magnetization is rather uniform in most of the particle. When an in‐plane field is applied exactly along the hard axis, a complex domain structure is formed, so that the remanence is zero, in agreement with experiment. Formation of this state requires that the applied field exceed a critical value. Upon application of an easy axis field to this complex state, the domain structure is shifted so that the magnetization increases linearly with the applied field.
56 citations
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TL;DR: The magnetic domain structures in ultrathin fcc cobalt films, epitaxially grown on Cu(100), have been investigated by means of a scanning electron microscope with spin polarization analysis of the secondary electrons as discussed by the authors.
47 citations
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TL;DR: In this paper, a Chua-type magnetization model based on magnetic domain theory is applied to typical ferromagnetic materials, such as iron, ferrite, and amorphous magnetic material.
Abstract: In order to calculate the magnetodynamic fields exactly, it is essential to work out a magnetization model. We have previously proposed a Chua‐type magnetization model based on magnetic domain theory. This Chua‐type model is now applied to typical ferromagnetic materials, such as iron, ferrite, and amorphous magnetic material. As a result, it is revealed that the typical magnetization characteristics of representative ferromagnetic materials can be satisfactory reproduced by our Chua‐type model.
28 citations
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TL;DR: In this paper, an explanation based on the Stoner-wohlfarth model was proposed for thermal activation in a disordered system of BaFe 12 O 19 particles, which accounts for the Hopkinson effect.
27 citations
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TL;DR: In this article, an attempt is made to find an experimental correlation between the presence and strength of the interactions and the magnetization reversal of the particles, investigated by rotational hysteresis measurements and by the evolution of the angular dependence of the coercivity in samples of iron oxides at different dilution degrees.
Abstract: In an assembly of particles, as used in magnetic recording media, there are always magnetic interactions. The magnetic properties of the media are modified as a consequence of the effect of such interactions on the magnetic behavior of the particles. In this work an attempt is made to find an experimental correlation between the presence and strength of the interactions and the magnetization reversal of the particles. The reversal mode is investigated by rotational hysteresis measurements and by the evolution of the angular dependence of the coercivity in samples of iron oxides at different dilution degrees. The magnetic interactions are evaluated with measurements of the remanence curves. It is found that when the magnetic interactions among the particles increase, the parameters used to study the reversal mode evolve from the behavior typical of the incoherent magnetization processes to behaviors which can be considered as intermediate between coherent and incoherent reversal modes. This evolution can b...
24 citations
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TL;DR: Magnetic coercivity and squareness of various Fe3O4 particle systems have been investigated as a function of particle size and packing density in this paper, and it has been found that these particle systems, exhibiting considerable deviations from spherical symmetry, have magnetic coercivities and squares which are almost independent of packing density.
Abstract: Magnetic coercivity and squareness of various Fe3O4 particle systems have been investigated as a function of particle size and packing density. It has been found that these particle systems, exhibiting considerable deviations from spherical symmetry, have magnetic coercivities and squareness which are almost independent of packing density.
22 citations
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TL;DR: In this article, a novel fiber optic magnetometer based on the Faraday effect in a magnetic garnet thin-film ridged waveguide is described, where planar magnetization aligned parallel and antiparallel to the light propagation direction is generated by a gradient bias field, and a single domain wall crosses the light path.
Abstract: A novel fiber optic magnetometer based on the Faraday effect in a magnetic garnet thin‐film ridged waveguide is described. The single‐mode film has planar magnetization aligned parallel and antiparallel to the light propagation direction by a gradient bias field, and a single domain wall crosses the light path. The motion of this wall in response to an applied field changes the Faraday rotation in the film. Operation of this field or current sensor in both the transmission mode and the single fiber reflection mode has been demonstrated. Optical output varying linearly with ac or dc fields up to 15 Oe, with a minimum detectable field of 0.05 Oe, has been observed. This domain wall motion scheme in a zero birefringence waveguide can also be used in a polarization controller.
21 citations
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TL;DR: In this paper, it was shown that when these approximations are eliminated, a very small magnetic particle can never be completely saturated, even though such a state can be a very good approximation to the physical reality.
Abstract: An attempt to calculate exchange and magnetostatic energies for several discrete atoms, which can only be done for larger interatomic distances, is discussed. All estimations of the single-domain particle size are based on certain approximations which apply to a continuous material, but break down in the limit of discrete atoms. It is shown that when these approximations are eliminated, a very small magnetic particle can never be completely saturated, even though such a state can be a very good approximation to the physical reality. The previous micromagnetic calculations are only approximately valid, which resolves the Brown paradox. >
21 citations
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TL;DR: The spatial structure of reactants in the two-species annihilation reaction A+B→0 is described in this paper, where the distribution of domain sizes and the distributions of nearest-neighbor distances between particles of the same and of opposite species are investigated.
Abstract: The spatial structure of reactants in the two-species annihilation reaction A+B→0 is described. In one dimension, we investigate the distribution of domain sizes and the distributions of nearest-neighbor distances between particles of the same and of opposite species. The latter two quantities are characterized by a new length scale which is intermediate to the domain size t1/2 and the typical interparticle spacing t1/4. A scaling argument suggests that the typical distance between particles of opposite species, or equivalently the gaps between domains, grows astζ, with ζ = 3/8 and 1/3, respectively, in spatial dimensiond=1 and 2. The average density profile of a single domain is spatially nonuniform, with the density decaying to zero linearly as the domain edge is approached. This behavior permits a determination of the distribution of nearest-neighbor distances of same-species reactants. The corresponding moments of this distribution exhibit multiscaling which involves geometric averages of different powers of the domain size and the interparticle spacing.
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TL;DR: In this article, the grain size dependence of intrinsic coercivity Hc of sintered Nd-Fe-B permanent magnets is investigated, and it is confirmed that small grain sizes are connected with high Hc values, and that for magnets with different grain sizes, their coercivity can be expressed by the formula μ0Hc=Ne(kμ0HA−NiIs), where HA and Is denote the magnetic anisotropy field and spontaneous magnetization of the hard magnetic Nd2Fe14B phase, respectively, and Ne a parameter inversely changing with
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TL;DR: In this article, a simple model of domain structure is used to determine the particle size, mineralogical, stress and temperature dependence of the LEM domain states available to fine particles of magnetite and titanomagnetite (TM56).
Abstract: The domain state (single domain versus multidomain) of fine magnetic particles has long been associated with their remanent and hysteresis properties. Both domain observations and micromagnetic theory indicate that a large number of local energy minimum (LEM) domain states are available to single domain and multidomain particles. Theoretical calculations based on a simple model of domain structure are made to determine the particle size, mineralogical, stress and temperature dependence of the LEM domain states available to fine particles of magnetite and titanomagnetite (TM56). The global (or absolute) energy minimum (AEM) domain state depends primarily on the balance between magnetostatic and exchange energies and shows only a weak temperature dependence. The range of local energy minima (LEM) domain states depends primarily on the anisotropy energies (magnetocrystalline and magnetoelastic) and is strongly temperature dependent. From the evolution of domain structure as a function of temperature and grain size implied from the domain state calculations, the relative stabilities of Thermoremanent Magnetization (TRM), grain growth Chemical Remanent Magnetization (CRM) and trans-domain Viscous Remanent Magnetization (VRM) are discussed. The magnetic behavior of an ensemble of fine particles will depend on the LEM states initially occupied by the particles.
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TL;DR: In this article, the authors describe S = 1/2 Ising-like magnetic chains completely in terms of domain walls and find that a single domain wall behaves like a free particle in a well.
Abstract: The authors describe S=1/2 Ising-like magnetic chains completely in terms of domain walls. They formulate domain wall creation and annihilation operators as fermion operators and calculate the domain wall content of the ground state and of excited states. From exact results for finite chains and from the solution in the one-domain wall subspace they find that a single domain wall behaves like a free particle in a well. The transition between the two equivalent ground states of Ising-like S=1/2 chains is found to be dominated by quantum diffusion: the approach of the magnetization to the asymptotic behaviour is algebraic and not exponential. The analogy of this observation to interface fluctuations in the two-dimensional classical system is pointed out. For domain walls in the presence of impurities they study the phase shift and the transmission coefficient as well as the exact energy spectrum of finite impure lattices. To visualize the domain wall scattering they also demonstrate their real-time dynamics.
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TL;DR: In this article, the magneto-optical Kerr effect was used to investigate the domain width of Fe 14 Nd 2 B single crystal plates with different thicknesses and of grains of FeNdB-sintermagnets.
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01 Jan 1991
TL;DR: In this article, the magnetic configuration of the system is an energy minimum in the field, although it may not be the lowest energy minimum, and magnetization reversal takes place at H = He, the coercive field.
Abstract: Coercivity is the essential property characterizing hard magnetic materials, in particular with respect to normal ferromagnets. It exists when low field domain wall motion does not take place, either the magnetization being already saturated in zero field, or domain walls being pinned at structural heterogeneities. In these two cases, the magnetic configuration of the system is an energy minimum in the field, although it may not be the lowest energy minimum. This energy minimum vanishes at H = He, the coercive field. Then magnetization reversal takes place and the system reaches the lowest energy state.
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TL;DR: In this paper, the authors used a two-dimensional vector vibrating sample magnetometer (VSM) to obtain the correct angular dependence of the coercivity and of the remanent magnetization.
Abstract: Metal evaporated (ME) tape is being developed as an advanced medium for high‐density magnetic tape recording. It is produced by evaporation in an oxygen atmosphere, and consists of very small Co and CoNi crystallites intermingled with oxides of Co and Ni. The angle of incidence of the vapor flux is varied continuously during deposition, imparting to the film a distinct curved columnar structure. Previous studies have measured the angular dependence of the coercivity and remanence out of the plane of the tape in order to determine the preferred direction of magnetic anisotropy and the mechanism of magnetization reversal in these films. These studies, however, do not take into account the demagnetizing field. In this study, we used a two‐dimensional vector vibrating‐sample magnetometer (VSM) to obtain the correct angular dependence of the coercivity and of the remanent magnetization. Our results show that magnetization reversal near the easy axis proceeds by incoherent rotation, and not by domain‐wall displ...
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TL;DR: In this article, the authors experimentally verify the theoretical predictions regarding the influence of the particle parameters by measuring different sets of experimental tapes prepared with appropriate pigment samples, and show that the magnetic homogeneity as expressed by (1-S*) becomes increasingly important.
Abstract: With recorded wavelengths well under 1 micron the geometric dimensions of the particles start to have significant influence on the output of particulate media. The recorded wavelengths of well under 1 micron being used in video storage approach the length dimensions of standard recording pigments. As a single domain particle cannot support a magnetic transition along its length, the finite length of the particle leads to a reduction in the maximum output signal analogous to the gap loss function and known as length loss. At the same time also the magnetic homogeneity as expressed by (1-S*) becomes increasingly important. The authors experimentally verify the theoretical predictions regarding the influence of the particle parameters by measuring different sets of experimental tapes prepared with appropriate pigment samples. >
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TL;DR: In this article, the authors studied the four stages of magnetization reversal processes in oriented sintered Nd-Fe-B magnet after saturation magnetization along its easy direction.
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TL;DR: In this paper, Monte Carlo simulation is carried out to examine the formation of single domain Si(100) surfaces and the effect of annealing on rough surfaces produced by growth simulation.
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TL;DR: In this paper, the dependence of specific saturation magnetization on the particle size of pure and Co-Ti-substituted Ba-ferrites was interpreted in terms of a nonmagnetic surface layer parallel to thec-planes of 1.3 nm and 0.7 nm, respectively, in thickness.
Abstract: The dependence of the specific saturation magnetization on the particle size of pure and Co-Ti-substituted Ba-ferrites was interpreted in terms of a nonmagnetic surface layer parallel to thec-planes of 1.3 nm and 0.7 nm, respectively, in thickness. Electron microscope investigations of the particles demonstrate that this effect arises neither from a sufficient fraction of superparamagnetic particles in the ensemble nor from the Co-Ti substitution or from surface defects such as steps and stacking disorder of the building blocks. Extrapolating this surface effect to small sizes yields a critical size, with the particles losing their ferrimagnetic behaviour. This critical size agrees surprisingly well with the volume calculated for the transition of the single domain state to the superparamagnetic one.
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TL;DR: The Landau-Ginzburg model is applied to a uniaxial ferromagnet including the possibility of magnetic inhomogeneities in the sample to study the effects of external magnetic fields on the various homogeneous and inhomogeneous magnetic structures that minimize the free energy.
Abstract: In this paper we apply the Landau-Ginzburg model to a uniaxial ferromagnet including the possibility of magnetic inhomogeneities in the sample. The effects of external magnetic fields on the various homogeneous and inhomogeneous magnetic structures that minimize the free energy are studied. Using exact methods of nonlinear analysis, space-dependent solutions of the equation of state are found, and their mean magnetizations are calculated. A combination of analytical and numerical methods is then employed in the study of their energies. Finally, the role of various magnetization patterns is investigated in the Arrott plots for magnetization processes.
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TL;DR: In this paper, the authors calculated the field and temperature dependence of viscous acquisition by numerical two-dimensional integration, using experimentally determined volume and switching field distributions, with especially strong discrepancies below the Verwey transition.
Abstract: The acquisition of viscous magnetization has been measured on a single domain magnetite sample in the temperature range 80 to 330 K and in applied fields up to 1540 Oe. Based on Neel’s single domain theory, we have calculated the field and temperature dependence of viscous acquisition by numerical two‐dimensional integration, using experimentally determined volume and switching field distributions. Predicted and experimental viscosity coefficients do not match, with especially strong discrepancies below the Verwey transition. The experimental acquisition coefficient is larger below the transition than at room temperature, even though the corresponding switching field distributions are nearly identical. Thus we cannot explain single domain viscosity by switching field and volume distributions alone, and we suspect that stress plays a prominent role.
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TL;DR: Magnetic properties of RCo 2 X 2 compounds have been studied throughout high-field magnetization measurements in the magnetic field up to 140 kOe and in the temperature range: 4.2-283 K as mentioned in this paper.
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TL;DR: In this article, a set of coupled equations of the following kinds are proposed to describe the simultaneous rotations of the magnetization vectors and the displacements of curved domain walls in one pair of magnetostatically coupled magnetic films separated by a variable distance.
Abstract: General equations are proposed to describe the simultaneous rotations of the magnetization vectors and the displacements of curved domain walls in one pair of magnetostatically coupled magnetic films separated by a variable distance. Leakage‐field energy is written in the ‘‘transmission‐line’’ approximation. The effects of dissipation and the constraint of flux continuity across a domain wall are handled by d’Alembert’s virtual work principle. The result is a set of coupled equations of the following kinds: (1) dynamic torque balance at each point inside a domain, (2) wall‐domain constraint due to flux continuity, (3) boundary condition on domain magnetization which depends on instantaneous wall positions, and (4) wall velocity. Within certain limitations these equations apply to the core of an inductive magnetic recording head.
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TL;DR: In this article, the field-induced transitions in quasi-ternary Er2Fe14B compounds have been revealed by means of magnetization measurements at high magnetic fields, in particular the modest differential high-field susceptibility and the formation of a non-collinear magnetic structure at 42 T.
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IBM1
TL;DR: In this paper, the authors derived general equations to describe the simultaneous nonuniform planar rotations of the magnetization vector and displacements of curved domain walls and their junctions in soft magnetic films.
Abstract: General equations are derived to describe the simultaneous nonuniform planar rotations of the magnetization vector and displacements of curved domain walls and their junctions in soft magnetic films. These equations take into account effects of exchange stiffness, magnetic anisotropy, external and either long- or short-range demagnetizing fields, wall energy, and dissipation. The case of a matched film pair using the capacitor or transmission-surface approximation for its short-range demagnetizing energy is considered. The theory is founded on energy and dissipation functionals including domain and wall terms. The constraint of wall-normal magnetization continuity across a domain wall is handled by a method of implementing d'Alembert's virtual work principle without introducing Lagrange multipliers. The result is a set of coupled equations expressing the dynamic torque balance at points inside domains, the wall-domain constraint due to wall-normal magnetization continuity, an additional boundary condition coupling domain magnetization and wall curves, and the wall velocity. >
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TL;DR: In this paper, a two-dimensional grid system representing the magnetization direction in a magnetic film plane was used to study the wall coercivity caused by magnetic nonuniformity.
Abstract: The wall coercivity caused by the magnetic nonuniformity has been studied numerically. The Landau‐Lifshits‐Gilbert (LLG) equation is integrated by an explicit scheme of the modified Dufort‐Frankel method. The computation was carried out for a two‐dimensional grid system representing the magnetization direction in a magnetic film plane. Typical magnetic parameters for magneto‐optic recording media were assumed. Spatial variations of uniaxial anisotropy were treated as the magnetic nonuniformity. The validity of our numerical approach was demonstrated with preliminary one‐dimensional computations, compared to analytical solutions. A wall coercive field of 2.5 kOe was observed for the wall coupling with a pinning site (30‐A width and 360‐A spacing along the wall) of 10 times larger anisotropy compared to the ordinary region. A two‐dimensional anisotropy variation (K=106–107 erg/cm3) with a wavelength larger than 60 A also caused a wall coercivity on the order of 1 kOe, compared to those in magneto‐optic recording media. It was also found that a fine pinning site on the order of 100 A caused a notable coercivity for the bubble domain wall surrounding it.
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TL;DR: In this paper, the remanent magnetic moment of essentially antiferromagnetic goethite was investigated and the previous experimental results were compared to the predictions of the theory for a single domain particles assembly.
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TL;DR: In this paper, the authors obtained the full magnetization curve of high J c samples YBa 2 Cu 3 O 7−x grown by the MPMG method up to 100T and found that the magnetization hysteresis persists in the field as high as 100T, indicating a large critical current even at such high fields.
Abstract: We have obtained the full magnetization curve of high J c samples YBa 2 Cu 3 O 7−x grown by the MPMG method up to 100T. For magnetic fields parallel to the ab plane, we found that the magnetization hysteresis persists in the field as high as 100T, indicating a large critical current even at such high fields.