Showing papers on "Magnetization published in 1994"
TL;DR: The study of cooperative phenomena in magnetism has provided fertile ground for testing theories of interacting systems that possess different spatial dimensions, ranges, and sign of interactions, and that exhibit local anisotropy of the basic interacting unit, the magnetic spin this paper.
Abstract: The study of cooperative phenomena in magnetism has provided fertile ground for testing theories of interacting systems that possess different spatial dimensions, ranges, and sign of interactions, and that exhibit local anisotropy of the basic interacting unit, the magnetic spin. This study has also motivated the development of new classes of materials, from the oldest known type of magnets, namely ferromagnets, to modern substances embodied in the unusual random field and spin glass compounds. In this context, we use the term material class to mean a set of compounds that share both microscopic, as well as macroscopic, or bulk, properties. Thus for example, ferro magnets possess the microscopic uniform ferromagnetic type exchange or dipolar interaction between spins, in addition to a bulk low temperature magnetization approaching the theoretical saturated moment value, and characteristic critical behavior at the Curie, or order ing, temperature. Among the known classes of magnets, spin glasses are among the most fascinating, displaying in their bulk properties simul taneous sharp ordering features in their magnetic response while exhibiting no such anomalies in their thermal response (1). These properties are thought to arise from a ground state characterized not by a single potential well representing the uniform arrangement of perfectly ordered spins, as in a ferromagnet, but rather by an energy landscape with many nearly degenerate ground state configurations separated by barriers of random height ( 1 ). The microscopic parameters empirically associated with spin glass
1,293 citations
TL;DR: In this paper, the Dzyaloshinsky interaction was used to stabilize magnetic vortices in uniaxial ferromagnetic materials by numerically solving the differential equations in the circular cell approximation.
990 citations
TL;DR: An improved water-suppression technique called WET (water suppression enhanced through T1 effects), developed from a Bloch equation analysis of the longitudinal magnetization over the T1 and B1 ranges of interest, achieves T1- and B 1-insensitive suppression with four RF pulses, each having a numerically optimized flip angle.
676 citations
TL;DR: In this paper, a dc magnetization measurement of Nd1+xBa2−xCu3Oy (Nd123) superconductors was performed in a reduced oxygen atmosphere.
Abstract: A reduced oxygen atmosphere during melt processing turned out to be critical for the fabrication of NdBa2Cu3Oy (Nd123) superconductors possessing high superconducting transition temperature (Tc) with a sharp transition and large critical current density (Jc) at 77 K. In a dc magnetization measurement, Nd123 superconductors melt processed in flowing a mixture gas of 1% O2 in Ar exhibited the Tc of about 95 K and the transition width of 1.5 K with the applied field of 10 Oe. A four‐probe measurement showed the zero resistive transition Tc (R=0) of about 95 K. An anomalous peak effect in the magnetization hysteresis (M‐H) loops was commonly observed and lead to large magnetic Jc of 2×104 A/cm2 at 77 K and 2 T for the applied field H parallel to the c axis of a sample (H∥c). This achievement is attributable to a preferential formation of high Tc phase (x<0.1) among the Nd1+xBa2−xCu3Oy solid solutions in a reduced oxygen atmosphere.
602 citations
TL;DR: In this paper, the authors show that the resistivity changes with the magnitude of temperature or field-induced magnetization in a single crystal of La 1-x Sr x MnO 3 near the critical composition (x ≈ 0.17).
Abstract: Giant magnetotransport phenomena including the field-induced nonmetal-metal transition have been found in single crystals of La 1- x Sr x MnO 3 near the critical composition ( x ≈0.17) for the nonmetal-metal transition and in the temperature region around the magnetic phase transition. Change of the resistivity shows a universal curve as a function of the magnitude of temperature- or field-induced magnetization, the most of which agrees with the prediction by the D =∞ and S =∞ Kondo lattice model with strong ferromagnetic (Hund) coupling.
555 citations
TL;DR: Numerical micromagnetic calculations rigorously describe the correlation between the microstructure and the magnetic properties of nanocrystalline permanent magnets, which shows remarkable high-energy products.
Abstract: Numerical micromagnetic calculations rigorously describe the correlation between the microstructure and the magnetic properties of nanocrystalline permanent magnets. In isotropic nanocrystalline permanent magnets exchange interactions override the anisotropy of the individual grains. Therefore the spontaneous magnetic polarization deviates from the easy axes in a region along the grain boundaries. For a fine grain structure with a mean grain size d20 nm the remanence is considerably enhanced, since the volume fraction of the boundary regions where the spontaneous magnetic polarization points towards the direction of the applied field becomes significantly high. The inhomogeneous ground state, however, favors the nucleation of reversed domains leading to a reduction of the coercive field with decreasing grain size. A uniform grain structure with a very small range in grain size avoids large demagnetizing fields and thus preserves a high coercivity. For a grain size of 10 nm isotropic two-phase permanent magnets based on ${\mathrm{Fe}}_{14}$${\mathrm{Nd}}_{2}$B and \ensuremath{\alpha}-Fe show remarkable high-energy products, because the volume fraction of the magnetically soft phase can be increased up to 50% without a significant loss of coercivity.
530 citations
TL;DR: The critical-state behavior of an infinitely long type-II superconducting thin-film strip is theoretically analyzed for an arbitrary sequence of applied transport currents and perpendicular magnetic fields.
Abstract: The critical-state behavior of an infinitely long type-II superconducting thin-film strip is theoretically analyzed for an arbitrary sequence of applied transport currents and perpendicular magnetic fields. Included are solutions for applied field only, transport current only, transport current applied to a sample initially in the remanent critical state, ac applied field, ac transport current, and simultaneously applied field and transport current. The results are compared side by side with corresponding solutions for the more famililar slab geometry; there are striking differences in behavior.
479 citations
TL;DR: In this article, a simple model accounts for the time-scale dependence of coercivity in terms of the thermally assisted crossing of an energy barrier whose height is reduced by the applied field.
Abstract: Coercivity and other experimental measures of switching field depend upon the time scale of interest. This time‐scale dependence has practical importance in magnetic recording, because the effective time scales of writing and storage are very different. A simple model accounts for the time‐scale dependence of coercivity in terms of the thermally assisted crossing of an energy barrier whose height is reduced by the applied field. Fitting this barrier‐crossing model to data provides an estimate of the volume that must switch magnetization direction in overcoming the barrier. The assumption of Stoner–Wohlfarth reversal is used to obtain an initial estimate of the dependence of the barrier height on the field. With some adjustment of the resulting energy expression, the model gives good agreement between calculated switching volume and actual particle volume for advanced recording particles of three types: acicular oxide, acicular metal, and barium ferrite platelets. The model can be used to estimate minimum ...
465 citations
TL;DR: A theoretical description of vortex dynamics in thin flat samples is derived and is found to compare favorably with experimental results, finding a vortex concentration in the center of the sample and a zero-field peak in the magnetization loops.
Abstract: A theoretical description of vortex dynamics in thin flat samples is derived and is found to compare favorably with experimental results. In perpendicular applied magnetic field the vortex penetration is delayed significantly due to the presence of a potential barrier of geometrical origin. This novel geometrical barrier effect results in hysteretic magnetization and in the existence of an irreversibility line in the absence of bulk pinning. Among the unique characteristics of the barrier are a vortex concentration in the center of the sample and a zero-field peak in the magnetization loops.
395 citations
TL;DR: In this article, it was shown that the peak magnetoresistance peak occurs not at the temperature of magnetic transition but at a temperature where the magnetization is still substantial, the spin disorder scattering is not likely to be the main mechanism in these highly magnetoresistive films.
Abstract: Colossal magnetoresistance with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La‐Ca‐Mn‐O thin films. This magnetoresistance value is about three orders of magnitude higher than is typically seen in the giant‐magnetoresistance‐type metallic, superlattice films. The temperature of peak magnetoresistance is located in the region of metallic resistivity behavior. As the magnetoresistance peak occurs not at the temperature of magnetic transition but at a temperature where the magnetization is still substantial, the spin‐disorder scattering is not likely to be the main mechanism in these highly magnetoresistive films. The peak can be shifted to near room temperature by adjusting processing parameters. Near‐room‐temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be very detrimental to achieving large magnetoresistance in the lanthanum manganite compounds. The fact th...
358 citations
TL;DR: In this paper, the spin-glass behavior is attributed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co 3+ and Co 4+ and the antiferromagnetic one between like spins.
Abstract: Magnetic properties of La 1- x Sr x CoO 3 (0 ≤ x ≤0.5) have been studied by magnetization measurements in low magnetic fields. It has been found that there exist spin-glass (0< x ≤0.18) and cluster-glass (0.18 ≤ x ≤0.5) regions. Ferromagnetic long-range order previously reported does not take place. Spin-glass behavior is ascribed to the frustration of random competing exchange interactions, namely the ferromagnetic double-exchange interaction between Co 3+ and Co 4+ and the antiferromagnetic one between like spins.
TL;DR: In this paper, a quantum magnetic disk scheme that is based on uniformly embedding single-domain magnetic structures in a nonmagnetic disk is proposed, which can be used to store one bit of information, therefore such nanomagnetic pillar array storage offers a rather different paradigm than the conventional storage method.
Abstract: Using electron beam nanolithography and electroplating, arrays of Ni pillars on silicon that have a uniform diameter of 35 nm, a height of 120 nm, and a period of 100 nm were fabricated. The density of the pillar arrays is 65 Gbits/in.2—over two orders of magnitude greater than the state‐of‐the‐art magnetic storage density. Because of their nanoscale size, shape anisotropy, and separation from each other, each Ni pillar is single domain with only two quantized perpendicular magnetization states: up and down. Each pillar can be used to store one bit of information, therefore such nanomagnetic pillar array storage offers a rather different paradigm than the conventional storage method. A quantum magnetic disk scheme that is based on uniformly embedding single‐domain magnetic structures in a nonmagnetic disk is proposed.
TL;DR: The easy axis of magnetization in Ni/Cu(001) films exhibits a crossover from in-plane to perpendicular orientation with increasing film thickness, which can be extrapolated from thin-film data.
Abstract: The easy axis of magnetization in Ni/Cu(001) films exhibits a crossover from in-plane to perpendicular orientation with increasing film thickness. This reorientation at \ensuremath{\approxeq}7 monolayers, observed by ferromagnetic resonance, is substantially different from previous findings for Fe and Co films and can be extrapolated from thin-film data. The artificial lattice structure of Ni on Cu yields within magnetoelasticity theory a volume anisotropy of 29 \ensuremath{\mu}eV/atom agreeing perfectly with experiment. In thinner films the surface anisotropy of -77 \ensuremath{\mu}eV/atom dominates.
TL;DR: This work calculates hysteretic magnetization curves and ac-susceptibility components for a type-II superconducting thin circular disk subjected to a low-frequency oscillating applied field and shows how [chi][prime][prime] is simply related to the ac loss per cycle per unit volume.
Abstract: We calculate hysteretic magnetization curves and ac-susceptibility components [chi][sub [ital n]][sup [prime]] and [chi][sub [ital n]][sup [prime][prime]] for [ital n]=1, 3, and 5 for a type-II superconducting thin circular disk subjected to a low-frequency oscillating applied field, extending previous approaches for calculating hysteretic current-density and magnetic flux-density profiles in the critical state. We also present limiting expressions for [chi][prime]=[chi][sub 1][sup [prime]] and [chi][prime][prime]=[chi][sub 1][sup [prime][prime]] for both small and large values of the ac field amplitude, and we show how [chi][prime][prime] is simply related to the ac loss per cycle per unit volume. Finally, a comparison is made between our results and those obtained for slab and strip geometries.
TL;DR: In this paper, a colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La•Ca•Mn•O thin films.
Abstract: A colossal magnetoresistance effect with more than a thousandfold change in resistivity (ΔR/RH=127 000% at 77 K, H=6 T) has been obtained in epitaxially grown La‐Ca‐Mn‐O thin films. The effect is negative and isotropic with respect to the field orientations. The magnetoresistance is strongly temperature dependent, and exhibits a sharp peak that can be shifted to near room temperature by adjusting processing parameters. Near‐room‐temperature ΔR/RH values of ∼1300% at 260 K and ∼400% at 280 K have been observed. The presence of grain boundaries appears to be detrimental to achieving very large magnetoresistance in the lanthanum manganite films. The orders of magnitude change in electrical resistivity could be useful for various magnetic and electric device applications.
TL;DR: In this article, the interparticle forces and resulting shear stresses in a magnetorheological fluid are calculated from a finite element analysis in which the nonlinearity and saturation of the particle magnetization are incorporated.
Abstract: The interparticle forces and resulting shear stresses in a magnetorheological fluid are calculated. The field due to a linear chain of particles in a fixed average magnetic induction Bave is determined from a finite element analysis in which the nonlinearity and saturation of the particle magnetization are incorporated. The shear stresses are then computed from the field using Maxwell’s stress tensor. The stresses obtained for all but the lowest magnetic inductions are controlled by the saturation of the magnetization in the contact regions of each particle. Identifying the maximum shear stress as a function of shear strain with the yield stress gives values in agreement with results reported for typical fluids. For high magnetic inductions the yield stress plateaus due to the complete saturation of the particle magnetization; the stress scales as the square of the saturation magnetization in this regime.
TL;DR: In this paper, a two-dimensional network structure, extended by Mn(II)-ox-Cr(III) bridges, has been determined from single crystal X-ray data and the structure is discussed in relation to the strategy for preparing molecular based ferromagnets and, in addition, it is a solution to the question of the dimensionality of the [MM′(ox) 3 ] n network, which in principle can extend two- or three-dimensionalally to the crystal lattice.
TL;DR: Intercalated layered materials comprising an organic dye and inorganic MPS3 exhibit both a large optical nonlinearity and magnetic ordering.
Abstract: Intercalated layered materials comprising an organic dye and inorganic MPS(3) [where M is either the manganese ion (Mn(2+)) or the cadmium ion (Cd(2+))] phases have been prepared. The intercalation process induces a spontaneous poling, giving rise to an efficiency of 750 times that of urea in second-harmonic generation for the cadmium derivative. In addition, the manganese derivative displays a permanent magnetization below 40 kelvin. Thus, these materials exhibit both a large optical nonlinearity and magnetic ordering.
TL;DR: In this paper, an empirical linear dependence of the specific saturation magnetization σs on the specific surface area Sa of the fine crystallites was obtained in the form of σS(S) = σ s(∞)(1 - ASa), where the slope A is different for γ-Fe2O3 and γCo 0.94O3 particles.
TL;DR: In this paper, the Kondo lattice model with Hund's ferromagnetic spin coupling is investigated as a microscopic model of the perovskite-type 3 d transitionmetal oxide La 1- x Sr x MnO 3.
Abstract: The Kondo lattice model with Hund's ferromagnetic spin coupling is investigated as a microscopic model of the perovskite-type 3 d transitionmetal oxide La 1- x Sr x MnO 3 . In the classical spin limit S =∞ and the infinite-dimensional limit D =∞, the one-body Green's function is exactly calculated. Transport properties of the system in the presence of magnetic fields are obtained. The giant magnetoresistance of this model, which is in good agreement with the experimental data of La 1- x Sr x MnO 3 , is explained by the spin-disorder scattering process.
TL;DR: In this paper, the magnetostriction, magnetization, and Young's moduli measurements made under constant magnetic field conditions and under constant flux conditions are reported, from these measurements, magnetomechanical coupling factors are calculated.
Abstract: Recently it was discovered that composites of Terfenol‐D alloys with an insulating binder produce very large magnetostrictions. Resistivities of these composites reach high values, making them attractive for high‐frequency applications which require small eddy current losses. In this paper the magnetostriction, magnetization, and Young’s moduli measurements made under constant magnetic field conditions and under constant flux conditions are reported. From these measurements, magnetomechanical coupling factors are calculated. The properties are compared to those of ordinary metallic Terfenol‐D and nickel. Two different types of composites were investigated. In the first type the composite has an isotropic structure and in the second type, anisotropic. It is shown that the anisotropic type is more desirable since it possesses both higher magnetostriction and higher coupling factors. It is also clearly shown that the magnetization process for the anisotropic type can be explained by a 180° domain wall motion followed by a magnetization rotation.
TL;DR: The results suggest that the magnetic moments in the doped compound freeze into a spin-glass state at low temperature, indicating that the high-temperature transition is not dominantly magnetic in origin.
Abstract: ${\mathrm{LaCoO}}_{3}$ exhibits two magnetic-electronic transitions, one near 90 K and a second near 500 K. A previous study of the paramagnetic scattering using polarized neutrons demonstrated that the low-temperature transition is associated with the thermal excitation of ${\mathrm{Co}}^{3+}$ ions from the low-spin to the high-spin state. In the present work, we extend the paramagnetic-scattering measurements up to a temperature of 700 K. We find that the magnetic-scattering intensity decreases monotonically for temperatures above 300 K, indicating that the high-temperature transition is not dominantly magnetic in origin. Furthermore, the anomalous thermal expansion associated with the low-temperature transition is measured and shown to be consistent with a simple theoretical model for the spin-state transition. For comparison, paramagnetic-scattering measurements for ${\mathrm{La}}_{0.92}$${\mathrm{Sr}}_{0.08}$${\mathrm{CoO}}_{3}$ are also presented. In this material the ferromagnetic correlations are substantially stronger than in the undoped compound, and no transition to the low-spin state is observed. Instead, the paramagnetic scattering increases steadily with decreasing temperature until saturating below 24 K, the same temperature at which the magnetization of the zero-field-cooled specimen shows a sharp cusp. These results suggest that the magnetic moments in the doped compound freeze into a spin-glass state at low temperature.
TL;DR: In this paper, the magnetoresistance and magnetization curves have been analyzed taking into account both the paramagnetic (PM) and ferromagnetic (FM) contributions that are observed to be present.
Abstract: Several series of thin films (∼3000 A) were fabricated by coevaporation of Co and Ag in a dual e‐beam UHV system at substrate temperatures, TS, between 300 and 500 K. The composition was varied between 23 and 54 at. % Co. The maximum measured magnetoresistance was 31% at room and 67% at nitrogen temperature. Magnetization and Rutherford backscattering measurements showed that the Co and Ag atoms are completely segregated for films deposited at TS≥400 K. The magnetoresistance (MR) and magnetization curves have been analyzed taking into account both the paramagnetic (PM) and ferromagnetic (FM) contributions that are observed to be present. The films having ≤32 at. % Co are entirely paramagnetic. The fraction of Co atoms in the ferromagnetic component increases monotonically with increasing TS and/or at. % Co. The average radii of the PM granules in the films having an MR effect of 25%–31% are ∼20–22 A with a minimum average separation of ∼10 A. The large MR values attained in both the PM and FM components a...
TL;DR: In this article, the second-order perturbation of spin-phonon interactions is used to obtain an upper limit of the pre-exponential factor in the Arrhenius law, consistent with the very large experimental value.
Abstract: The relaxation time of the magnetization of a big magnetic molecule is evaluated. Isotropic exchange is assumed to be dominant, resulting in a fixed spin modulus s (equal to 20 in the case of interest). A perturbation of the form ASz2 results from spin-orbit coupling and produces an energy barrier As2 which separates positive and negative values of Sz. Spin-phonon interactions are treated by second-order perturbation theory. An upper limit of the pre-exponential factor in the Arrhenius law is obtained, which is consistent with the very large experimental value.
TL;DR: In this paper, a fully analytical formulation is outlined for computing molecular magnetic susceptibilities and nuclear magnetic shieldings via a continuous change of origin of the electronic current density induced by an external magnetic field.
Abstract: A fully analytical formulation is outlined for computing molecular magnetic susceptibilities and nuclear magnetic shieldings via a continuous change of origin of the electronic current density induced by an external magnetic field. The change of origin is described in terms of a (continuous) arbitrary shift functiond(r). Coupled Hartree-Fock second-order magnetic properties of CH4 and CO2 molecules have been computed, using the special choiced(r)=r as generating function. A detailed analysis of results obtained with a variety of basis sets reveals that such a method is not as good as previously suggested. Large basis sets must be used to obtain accurate magnetic properties. On the other hand, all the components of theoretical nuclear magnetic shielding evaluated via this approach are independent of the origin of the vector potential. In general, theoretical magnetic susceptibilities depend linearly on the distance between different coordinate frames, but are origin independent for centre-symmetric molecules.
TL;DR: In this article, a Faraday force magnetometer was developed for static magnetization measurements at very low temperatures down to 100 mK and in fields up to 9 T. The magnetic force acting on a specimen located in the adiabatic vacuum chamber of a dilution refrigerator was detected by a newly designed load-sensing variable capacitor.
Abstract: A Faraday force magnetometer has been developed for static magnetization measurements at very low temperatures down to 100 mK and in fields up to 9 T. The magnetic force acting on a specimen located in the adiabatic vacuum chamber of a dilution refrigerator is detected by a newly designed load-sensing variable capacitor. Use of a superconducting magnet with gradient coils enables accurate measurement of magnetic moment with a resolution of better than 1×10-7 Am2 ( 1×10-4 emu). An application to magnetization measurements on the heavy-electron antiferromagnet CeB6 is presented.
TL;DR: In this paper, local density functional calculations and experimental magnetization studies on giant nickel carbonyl clusters are presented, and the results show convincingly that the effect of the carbonyls ligation is to quench completely the magnetic moments of the nickel atoms at the surface of the clusters, leaving the inner core metal atoms relatively unaffected.
Abstract: Local density functional calculations and experimental magnetization studies on giant nickel carbonyl clusters are presented. The results show convincingly that the effect of the carbonyl ligation is to quench completely the magnetic moments of the nickel atoms at the surface of the clusters, leaving the inner-core metal atoms relatively unaffected. The relation with surface coating of magnetic particles for recording media is pointed out.
TL;DR: A roughly linear scaling relation of the out-of-plane orbital moment [ital m][sub orb][sup [perpendicular]] with the intrinsic uniaxial anisotropy constant [ital K][sub [ital u],1][sup Co] per Co volume is observed.
Abstract: The out-of-plane orbital magnetic moment of Co in Co/X multilayers (X=Pd, Pt, and Ni) with perpendicular magnetic anisotropy has been investigated using x-ray magnetic-circular-dichroism spectroscopy. The orbital d moment per Co atom, ${\mathit{m}}_{\mathrm{orb}}^{\mathrm{\ensuremath{\perp}}}$, is considerably enhanced by (0.15\ifmmode\pm\else\textpm\fi{}0.02)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ and (0.07\ifmmode\pm\else\textpm\fi{}0.02)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ in Co/Pd and Co/Pt multilayers, respectively, compared with a single thick Co film. No respective enhancement is found in the case of Co/Ni. This enhancement does not scale with the spin-orbit coupling parameter ${\ensuremath{\xi}}_{\mathrm{SO}}$ of Ni-3d, Pd-4d, and Pt-5d bands despite strong d-d mixing which leads to the presence of ferromagnetic moments of Pd and Pt atoms. However, a roughly linear scaling relation of the out-of-plane orbital moment ${\mathit{m}}_{\mathrm{orb}}^{\mathrm{\ensuremath{\perp}}}$ with the intrinsic uniaxial anisotropy constant ${\mathit{K}}_{\mathit{u},1}^{\mathrm{Co}}$ per Co volume is observed. This experimental finding is interpreted in conjunction with recent ab initio and tight-binding band-structure calculations as evidence for a preferential enhancement of the out-of-plane orbital moment of Co in Co/Pd and Co/Pt multilayers.
TL;DR: In this paper, the progress of the research starting from the initial stage of study to obtain the design strategies to induce ferromagnetic interaction in organic crystals to the discovery of ferromagnetism in p-nitrophenyl nitronyl nitroxide (p-NPNN; C13H16N3O4).
Abstract: Recently, the transition to ferromagnetic order has been found in crystals of organic compounds not containing metallic elements. The progress of the research is reviewed starting from the initial stage of study to obtain the design strategies to induce ferromagnetic interaction in organic crystals to the discovery of ferromagnetism in p-nitrophenyl nitronyl nitroxide ( p-NPNN; C13H16N3O4). The recent development in the field of molecular magnetism is also described.
TL;DR: In this article, isolated magnetic vortices are stabilized by an antisymmetric exchange interaction, the so-called Dzyaloshinsky interaction, which can be represented as an energy contribution linear in the first spatial derivatives of the magnetization vector.
Abstract: Isolated magnetic vortices are stabilized by an antisymmetric exchange interaction, the so-called Dzyaloshinsky interaction, which can be represented as an energy contribution linear in the first spatial derivatives of the magnetization vector. In contrast, vortex lines are demonstrated to be unstable in the bulk of regular uniaxial ferromagnets. They collapse spontaneously under the influence of anisotropy or an applied magnetic field. In reduced units the differential equation for isolated vortices contains two parameters: the reduced magnetic field h along the crystal axis and the material parameter which describes the relative contribution of the Dzyaloshinsky interaction term. Isolated vortices turn out to be always metastable for large fields, independent of as long as this parameter is positive. At low or negative fields they become unstable by two different mechanisms depending on the -value, but altogether these micromagnetic structures turn out to be stable in a remarkably wide range of parameters. At the end possible applications are considered.