Showing papers on "Single domain published in 2001"
TL;DR: The magnetic behavior of 100 nm period arrays of Ni nanowires embedded in a highly ordered alumina pore matrix was characterized by magnetometry and magnetic force microscopy as discussed by the authors.
Abstract: The magnetic behavior of 100 nm period arrays of Ni nanowires embedded in a highly ordered alumina pore matrix were characterized by magnetometry and magnetic force microscopy. Reducing the diameter of the nanowires from 55 to 30 nm while keeping the interwire distance constant leads to increasing coercive fields from 600 to 1200 Oe and to increasing remanence from 30% to 100%. The domain structure of the arrays exhibits in the demagnetized state a labyrith-like pattern. These results show that stray field interactions of single domain nanowires are entirely dependent on the nanowire diameter.
531 citations
TL;DR: With increasing diameter and decreasing film thickness a metastable near single domain state can be obtained during the reversal process in an in-plane applied field.
Abstract: Measurements are reported on the magnetization reversal in submicron magnetic rings fabricated by high-resolution electron beam lithography and lift-off from cobalt thin films. For all dimensions investigated, with diameters of 300-800 nm and a thickness of 10-50 nm, the flux closure state is the stable magnetization configuration. However, with increasing diameter and decreasing film thickness a metastable near single domain state can be obtained during the reversal process in an in-plane applied field.
272 citations
Patent•
23 Nov 2001TL;DR: In this paper, a magnetic spin polarizing a magnetization rotation device with a memory and a writing process using such a device is configured to include an apparatus for polarizing the spin of electrons, including a magnetic layer having magnetization perpendicular to the plane of magnetization of respective first and second magnetic layers.
Abstract: A magnetic spin polarizing a magnetization rotation device with a memory and a writing process using such a device. The device is configured to include an apparatus for polarizing the spin of electrons, including a magnetic layer having magnetization perpendicular to the plane of magnetization of respective first and second magnetic layers. The magnetization of the second magnetic layer rotates within a plane, which is either the plane of the layer or a perpendicular plane.
198 citations
TL;DR: In this article, the authors examined experimental data and a theoretical model in order to provide a rigorous framework for interpreting first-order reversal curves (FORC diagrams) for samples that contain superparamagnetic particles.
Abstract: SUMMARY We have recently developed a technique for characterizing the magnetic components within natural particle assemblages. This technique is based on the transformation of magnetization data from first-order reversal curves (FORCs) into contour plots of a 2-D distribution function (FORC diagrams). FORC diagrams are useful for obtaining information about switching fields and interactions in magnetic particle systems. Here, we examine experimental data and a theoretical model in order to provide a rigorous framework for interpreting FORC diagrams for samples that contain superparamagnetic particles. We have found four distinct manifestations of thermal relaxation on FORC diagrams. First, thermal relaxation will shift the FORC distribution to lower coercivities. Second, at intermediate temperatures, thermal relaxation can generate a secondary peak about the origin of a FORC diagram. This secondary peak indicates that part of a singledomain particle assemblage has become superparamagnetic. At high enough temperatures, the primary peak of the FORC distribution will be located about the origin of a FORC diagram. Third, thermal relaxation can produce a small, but systematic, upward shift of a FORC distribution. Fourth, thermal relaxation will produce contours that lie near and parallel to the vertical axis in the lower quadrant of a FORC diagram. These manifestations make FORC diagrams a powerful tool for studying the effects of thermal relaxation (superparamagnetism) in bulk natural samples, particularly when the samples contain mixed magnetic particle assemblages.
196 citations
TL;DR: In this paper, the magnetic anisotropy and domain structure of cylindrical Co nanowires with length of 10 or 20 μm and diameters ranging from 30 to 450 nm are studied by means of magnetization and magnetic torque measurements, as well as magnetic force microscopy.
Abstract: The magnetic anisotropy and domain structure of electrodeposited cylindrical Co nanowires with length of 10 or 20 μm and diameters ranging from 30 to 450 nm are studied by means of magnetization and magnetic torque measurements, as well as magnetic force microscopy. Experimental results reveal that crystal anisotropy either concurs with shape anisotropy in maintaining the Co magnetization aligned along the wire or favours an orientation of the magnetization perpendicular to the wire, hence competing with shape anisotropy, depending on whether the diameter of the wires is smaller or larger than a critical diameter of 50 nm. This change of crystal anisotropy, originating in changes in the crystallographic structure of Co, is naturally found to strongly modify the zero (or small) field magnetic domain structure in the nanowires. Except for nanowires with parallel-to-wire crystal anisotropy (very small diameters) where single-domain behaviour may occur, the formation of magnetic domains is required to explain the experimental observations. The geometrical restriction imposed on the magnetization by the small lateral size of the wires proves to play an important role in the domain structures formed.
182 citations
TL;DR: In this paper, a model for coercivity in polycrystalline exchange-bias bilayers is presented, which includes two contributions for their enhanced coercivity, inhomogeneous reversal, and irreversible transitions in the antiferromagnetic grains.
Abstract: A model is presented for coercivity in polycrystalline exchange-bias bilayers. It includes two contributions for their enhanced coercivity, inhomogeneous reversal, and irreversible transitions in the antiferromagnetic grains. The model can be characterized in terms of a small number of dimensionless parameters, and its behavior has been determined through simulations of magnetic reversal for a range of values of these parameters. In these simulations, the first contribution to the coercivity arises from energy losses in the ferromagnet due to irreversible transitions over small, local energy barriers in the ferromagnetic film due to the inhomogeneous coupling to the antiferromagnet. This inhomogeneous reversal contributes to the coercivity at all temperatures. The second contribution to the coercivity arises from energy losses in the antiferromagnet due to irreversible transitions of the antiferromagnetic order in the grains. In the present model, the antiferromagnetic order only becomes unstable at nonzero temperature, so that this contribution to the coercivity only occurs at nonzero temperatures. In addition to the coercivity, the computed hysteresis loops are found to be asymmetric, and the loop shift is shown to differ from the grain-averaged unidirectional anisotropy.
179 citations
TL;DR: In this article, a combination of electron-beam lithography and liftoff technique on electron transparent membrane substrates was used to prepare submicron permalloy elements by using Lorentz transmission electron microscopy.
Abstract: Magnetic vortices play an important role in the switching behavior of micron- and submicron-sized ferromagnetic elements. We have prepared submicron permalloy elements by a combination of electron-beam lithography and liftoff technique on electron transparent membrane substrates. The magnetization reversal mechanism and the remanent magnetization configuration were observed by means of Lorentz transmission electron microscopy. In remanence, the investigated structures form a vortex configuration. In situ magnetizing experiments showed the possibility of adjusting the sense of magnetization rotation by introducing a slight geometric asymmetry to the otherwise circular nanostructures.
174 citations
TL;DR: In this article, a simple method to control the direction of the circulation of the magnetization in mesoscopic ring magnets, using a uniform magnetic field only, is presented, based on the nucleation free switching which occurs when the rings switch from the near-saturated state, referred to as the "onion state", to the flux-closed vortex state.
Abstract: We present a simple method to control the direction of the circulation of the magnetization in mesoscopic ring magnets, using a uniform magnetic field only. The method is based on the nucleation free switching which occurs when the rings switch from the near-saturated state, referred to as the “onion state,” to the flux-closed vortex state. Two possible onion states, forward or reverse magnetized, are possible for a given direction of the magnetic field. Going from the forward or the backward onion state, both local scanning Kerr microscopy measurements and micromagnetic simulations show that the clockwise or the counterclockwise vortex state, respectively, can be selected due to asymmetric pinning of the two domain walls that are present in the onion state.
130 citations
TL;DR: In this paper, the magnetic properties of interacting 12.4 nm Fe3O4 spinel ferrite particles were investigated by X-ray diffraction (XRD) line broadening and field dependent magnetic analysis.
96 citations
Posted Content•
TL;DR: In this paper, the authors reviewed the most important theories and experimental results concerning the magnetization reversal of single-domain particles, clusters and molecular clusters and showed that for very small systems or very low temperature, magnetization can reverse via quantum tunneling.
Abstract: Nanometer-sized magnetic particles have generated continuous interest as the study of their properties has proved to be scientifically and technologically very challenging. In this article we reviewed the most important theories and experimental results concerning the magnetization reversal of single-domain particles,clusters and molecular clusters. Sect.1 reviews briefly the commonly used measuring techniques. Among them, electrical transport measurements, Hall probes and micro-SQUID techniques seem to be the most convenient techniques for low temperature measurements. Sect.2 discusses the mechanisms of magnetization reversal in single domain particles at zero Kelvin. The influence of temperature on the magnetization reversal is reported in Sect.3. Finally, Sect.4 shows that for very small systems or very low temperature, magnetization can reverse via quantum tunneling. The boundary between classical and quantum physics has become a very attractive field of research. This section discusses detailed measurements which demonstrated that molecular magnets offer an unique opportunity to explore the quantum dynamics of a large but finite spin. We then discussed tunneling in nanoparticles and showed how one might give a definite proof of their quantum character at low temperature.
95 citations
TL;DR: In this paper, the magnetic domain structures of single-crystalline Ni48Mn31Ga21 prism with {1 − 0 − 0} faces were studied using scanning electron microscopy and by Bitter technique.
TL;DR: In this article, the authors described the magnetization tunneling of the direction of magnetization for two crystallographically different forms of [Mn12O12(O2CC6H4-p-Me)16(H2O)4] solvate.
TL;DR: In this paper, the magnetic properties of a monolayer of spherical and uniaxial single domain magnetic nanoparticles, with dipolar interaction, at vanishing temperature, were analyzed.
Abstract: We calculate the magnetic properties of a monolayer of spherical and uniaxial single domain magnetic nanoparticles, with dipolar interaction, at vanishing temperature. The particles are located on the sites of a lattice of either square or hexagonal structure. We focus on both the magnetic properties (magnetization curve, coercive field) and the orientational structure of the magnetic moments in the layer. We find that the structure of the lattice plays an important role on the orientational structure of the moments, especially in the case of a strong dipolar coupling: an ordered state takes place at a length scale of a few interparticle distances, the nature of which (ferromagnetic or antiferromagnetic) changes with the symmetry of the lattice. However, the magnetic properties are nearly independent of the structure of the lattice.
TL;DR: In this paper, magnetic force microscopy (MFM) was used to obtain a fine image of magnetic domain structure in Co/AAO film successfully, and the magnetic moment was aligned in the same direction after the sample was magnetized under a 1 T external field.
TL;DR: In this paper, the relative contrasts for small-angle scattering are strongly modi"ed which allows a precise evaluation of magnetization, density and composition at surfaces and interfaces of nanoscaled materials.
Abstract: Using polarized neutrons, the relative contrasts for small-angle scattering are strongly modi"ed which allows a precise evaluation of magnetization, density and composition pro"les at surfaces and interfaces of nanoscaled materials. In Co ferro#uids, the magnetic core behaves as a non-interacting single domain. The core is encapsulated by a shell of surfactant molecules which was found to be impenetrable for the solvent. In soft magnetic Fe}Si}B}(Nb,Cu) and Fe}Nb}B alloys, the presence of a weak magnetic interface between ferromagnetic nanocrystals and amorphous matrix has been demonstrated which breaks the exchange interactions. 2001 Elsevier Science B.V. All rights reserved.
TL;DR: In this paper, temperature and field dependencies of the velocity of domain wall propagation have been measured in the range of temperatures 5-300 K in amorphous Fe65B15Si15C5 glass-coated microwires.
Abstract: The temperature and field dependencies of the velocity of domain wall propagation have been measured in the range of temperatures 5–300 K in amorphous Fe65B15Si15C5 glass-coated microwires. The domain wall velocity within the experimental range of magnetic fields (65–100 A/m) and temperatures (5–300 K) was found between 35 and 65 m/s. Consequently, the domain wall mobility was estimated from these dependencies. The critical field for the domain wall propagation is below the switching field reflecting the existence of an energy barrier for the domain wall depinning.
31 May 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a series of conditions that are determinant for the preparation process of amorphous glass covered magnetic wires (AGCW) are presented as a function of composition and samples state.
Abstract: The amorphous glass covered magnetic wires (AGCW) are of great interest due to their specific magnetic properties that can be controlled through the composition as well as through the metallic core diameter and the thickness of the glass cover. The specific magnetic properties are determined by the magnitude of the magnetic anisotropies induced by the mechanical stresses due to the preparation process. This paper presents a series of conditions that are determinant for the preparation process of the AGCW. The basic magnetic characteristics of the highly positive, negative and nearly zero magnetostrictive AGCW are presented as a function of composition and samples state. Recently performed FMR measurements showed that the metal–glass interface influences the magnetic characteristics including the magnetic anisotropy. The magnetic domain structure of the highly positive AGCW presents a single domain axially magnetized with some closure domains at the ends of the wire while for the wires obtained after the glass removal it presents an axially magnetized inner core with a typical maze domain configuration at the surface of the wire.
TL;DR: It is shown that the Mel'nikov-Meshkov formalism for bridging the very low damping and intermediate-to-high damping Kramers escape rates as a function of the dissipation parameter for mechanical particles may be extended to the rotational Brownian motion of magnetic dipole moments of single-domain ferromagnetic particles in nonaxially symmetric potentials of the magnetocrystalline anisotropy.
Abstract: It is shown that the Mel'nikov-Meshkov formalism for bridging the very low damping (VLD) and intermediate-to-high damping (IHD) Kramers escape rates as a function of the dissipation parameter for mechanical particles may be extended to the rotational Brownian motion of magnetic dipole moments of single-domain ferromagnetic particles in nonaxially symmetric potentials of the magnetocrystalline anisotropy so that both regimes of damping occur. The procedure is illustrated by considering the particular nonaxially symmetric problem of superparamagnetic particles possessing uniaxial anisotropy subject to an external uniform field applied at an angle to the easy axis of magnetization. Here the Mel'nikov-Meshkov treatment is found to be in good agreement with an exact calculation of the smallest eigenvalue of Brown's Fokker-Planck equation, provided the external field is large enough to ensure significant departure from axial symmetry, so that the VLD and IHD formulas for escape rates of magnetic dipoles for nonaxially symmetric potentials are valid.
TL;DR: In this paper, the magnetic susceptibility was modelled for weakly-interacting assemblages of single domain (SD) grains of magnetite, near the SP and stable SD threshold known as the blocking volume.
Abstract: SUMMARY Environmental systems often contain superparamagnetic (SP) grains that cause a frequency dependency of low-field magnetic susceptibility ( ). Previous models for have been for non-interacting regimes, whereas environmental systems often display characteristics of magnetic interactions. In this paper, the magnetic susceptibility ( ) and have been modelled for weakly-interacting assemblages of single domain (SD) grains of magnetite, near the SP and stable SD threshold known as the blocking volume . Weak-interactions between SP grains effectively increase the anisotropy, which reduces . The relationship between the grain distribution and the reduced , causes a decrease in the peak values of , and can reduce by over 50 % for certain grain distributions. This helps to explain why values for natural samples are very rarely seen above 15 %, as the effect of interactions is seen to reduce maximum 20 % in non-interacting models to values 20 % for the same grain distribution. However, it is also found that the reduction of as a result of interactions can also increase for certain grain distributions. The model only accommodates weakly interacting systems, as the behaviour of strongly inter
TL;DR: In this article, the spin-reorientation transition (SRT) can be investigated by means of simple Kerr magnetometry, and a method to separate the longitudinal, polar, and equatorial magnetization components that may contribute to a mixed magneto-optical Kerr effect signal is presented.
Abstract: We present a method to separate the longitudinal, polar, and equatorial magnetization components that may contribute to a mixed magneto-optical Kerr-effect signal and demonstrate how the spin-reorientation transition (SRT) can be investigated by means of simple Kerr magnetometry. In a Co/Au(111) film with thickness within the SRT region we find hysteresis loops with nonvanishing remanence in all three components when a field is applied within the film plane. A vertical field, however, drives the same film into a single domain state exhibiting full remanence. The fact that remanence is found in all magnetization components, and full remanence is obtained in a vertical field, rules out that the transition proceeds via a state of canting of magnetization and indicates that it proceeds via a state of coexisting phases.
TL;DR: In this article, the authors measured hysteresis loops as a function of temperature between 10 K and room temperature for two size fractions of crushed magnetite: 1-5 μm (pseudo-single-domain, PSD) and 100-150 μm(multidomain, MD).
TL;DR: In this article, a spin-polarized scanning tunneling spectroscopy of nanoscale Fe islands with a height of two atomic layers, grown on a stepped W(110) surface and surrounded by a closed monolayer (ML) Fe was performed.
Abstract: We have performed low-temperature $(T=15\mathrm{K})$ spin-polarized scanning tunneling spectroscopy of nanoscale Fe islands with a height of two atomic layers, grown on a stepped W(110) surface and surrounded by a closed monolayer (ML) Fe. These islands are single domain particles up to a coverage of 1.5 pseudomorphic ML and keep an antiferromagnetic out-of-plane ordering far beyond the onset of their coalescence. For small islands we observe a reorientation to in-plane magnetization between 2 and 3 nm island width due to exchange coupling to the in-plane magnetized ML.
TL;DR: In this paper, double-shifted magnetization loops appear at a certain range of Co thickness, in which both the shift field and exchange bias field decreases as the Co film thickness increases.
Abstract: Ferromagnetic films of fcc (001) Co, epitaxially grown on a NiMn antiferromagnetic underlayer, exhibit double-shifted magnetization curves. Exchange coupling not only provides a unidirectional bias field but also induces a uniaxial anisotropy, breaking the biaxial symmetry of Co. The double-shifted magnetization loops appear at certain range of Co thickness, in which both the shift field and exchange-bias field decreases as the Co film thickness increases. An interesting starlike astroid was found and it suggested that an interfacial biquadratic coupling results in double-shifted magnetization curves.
TL;DR: In this article, the authors used magnetic force microscopy in combination with micromagnetic theory to obtain a mean switching field (coercive field) of 710 Oe for 100 nm period arrays of Ni nanomagnets.
Abstract: Macroscopic and microscopic switching characteristics are obtained for 100 nm period arrays of Ni nanomagnets with a mean switching field (coercive field) of 710 Oe. Magnetic force microscopy in combination with micromagnetic theory shows that inhomogeneities in the particle shapes result in an intrinsic standard deviation in switching fields of 105 Oe, while the interactions between neighboring nanomagnets broaden the distribution to 276 Oe, equivalent to a squareness of 0.8 in the bulk hysteresis loop. The switching field distribution is consistent with curling as the switching mechanism.
TL;DR: In this paper, a magnetic rectangular block array of 130 Gblock/in. was fabricated using focused ion beam lithography with a block size-to-period ratio of 0.85.
Abstract: We have fabricated a magnetic rectangular block array of 130 Gblock/in.2 with a block-size-to-period ratio of 0.85 by using focused ion beam lithography. Each block has perpendicular crystal magnetic anisotropy and a single domain structure. Its advantage as patterned media is discussed in conjunction with thermal stability in recorded magnetization, reading signal, and area density.
TL;DR: In this article, the authors performed magnetic force microscopy measurements on isolated 35 nm thick rectangular Co structures and showed that the transition from a magnetic single-domain state towards a magnetic multidomain state depends on the size and aspect ratio of the structures.
Abstract: We have performed magnetic force microscopy measurements on isolated 35 nm thick rectangular Co structures. The structures have a length L ranging between 0.25 and 10 μm and a width W ranging between 0.25 and 5.5 μm, covering aspect ratios m=L/W between 1 and 40. This enables us to map the transition from a magnetic single-domain state towards a magnetic multidomain state when increasing the size of the structures. This transition depends on the size as well as the aspect ratio of the structures. Our results can be interpreted in terms of the theoretical model developed by A. Aharoni [J. Appl. Phys. 63, 5879 (1988)].
TDK1
TL;DR: In this article, a CoPt dot array with diameters ranging from 80 to 1000 nm was fabricated by using electron beam lithography and reactive ion etching, which had their magnetic easy axes perpendicular to the plane.
TL;DR: In this article, the saturation remanence and remanent magnetization curves for noninteracting single-domain particles with cubic magnetocrystalline anisotropy have been calculated.
Abstract: Magnetization and remanent magnetization curves for noninteracting single-domain particles with cubic magnetocrystalline anisotropy have been calculated, taking into account the first two anisotropy constants. The dependencies of the saturation remanence, coercivity, remanence coercivity, and δM plots on the anisotropy constants ratio have been discussed. It has been found that the calculated saturation remanence shows maxima in the vicinity of the spin-reorientation transition points for both negative and positive first cubic anisotropy constants. The remanent magnetization for the case when the face diagonals 〈110〉 are the easiest magnetization orientations has been analytically determined as well. It has been shown that when more than one type of easiest directions coexist, the remanence of the system can only be obtained numerically because of the history dependence of the remanent magnetization for some particles’ configurations. The predicted remanence behavior for systems representing spin-reorient...
TL;DR: In this paper, the authors studied the hysteresis of composite systems consisting of nanosized ferromagnetic particles embedded in a nonmagnetic metal matrix using the Monte Carlo method.
Abstract: The hysteresis of composite systems consisting of nanosized ferromagnetic particles embedded in a nonmagnetic metal matrix is studied using the Monte Carlo method. In the model, the nanosized particles are assumed to be single domain and to possess random uniaxial anisotropy. The particles are well dispersed so that the interactions between them are weak and can be neglected. These particles may be superparamagnetic (unblocked) or not (blocked) depending on the temperature T, energy barrier ΔE, and measurement time τm. It is found that the hysteresis loop, which is obtained even in the absence of interparticle interactions, is mainly caused by the blocked particles as a result of the irreversible transitions between states of minimum energy. The remanence and coercivity of such systems decrease as T increases and disappear at high T. The results are in agreement with recent experimental observations.