Showing papers on "Single domain published in 2008"
TL;DR: It is shown that the manipulation of magnetization can be achieved solely by electric fields in a ferromagnetic semiconductor, (Ga,Mn)As, allowing manipulation of the magnetization direction.
Abstract: Conventional semiconductor devices use electric fields to control conductivity, a scalar quantity, for information processing. In magnetic materials, the direction of magnetization, a vector quantity, is of fundamental importance. In magnetic data storage, magnetization is manipulated with a current-generated magnetic field (Oersted-Ampere field), and spin current is being studied for use in non-volatile magnetic memories. To make control of magnetization fully compatible with semiconductor devices, it is highly desirable to control magnetization using electric fields. Conventionally, this is achieved by means of magnetostriction produced by mechanically generated strain through the use of piezoelectricity. Multiferroics have been widely studied in an alternative approach where ferroelectricity is combined with ferromagnetism. Magnetic-field control of electric polarization has been reported in these multiferroics using the magnetoelectric effect, but the inverse effect-direct electrical control of magnetization-has not so far been observed. Here we show that the manipulation of magnetization can be achieved solely by electric fields in a ferromagnetic semiconductor, (Ga,Mn)As. The magnetic anisotropy, which determines the magnetization direction, depends on the charge carrier (hole) concentration in (Ga,Mn)As. By applying an electric field using a metal-insulator-semiconductor structure, the hole concentration and, thereby, the magnetic anisotropy can be controlled, allowing manipulation of the magnetization direction.
615 citations
Book•
01 Jan 2008
TL;DR: In this article, the time-resolved X-ray Magnetic Circular Dichroism (X-Ray MRCD) was used for a selective probe of magnetization dynamics on nanosecond timescales.
Abstract: Fast Switching of Mesoscopic Magnets.- Spin Damping in Ultrathin Magnetic Films.- Magnetization Dynamics Investigated by Time-Resolved Kerr Effect Magnetometry.- High Speed Switching and Rotational Dynamics in Small Magnetic Thin Film Devices.- Time-Resolved X-Ray Magnetic Circular Dichroism - A Selective Probe of Magnetization Dynamics on Nanosecond Timescales.- The Dynamic Response of Magnetization to Hot Spins.- Ultrafast Magnetization and Switching Dynamics.- Laser-Induced Magnetization Dynamics.
589 citations
TL;DR: The ability to measure magnetization curves of individual magnetic atoms adsorbed on a nonmagnetic metallic substrate with use of a scanning tunneling microscope with a spin-polarized tip and map out low-energy magnetic interactions on the atomic scale is demonstrated.
Abstract: The miniaturization of magnetic devices toward the limit of single atoms calls for appropriate tools to study their magnetic properties. We demonstrate the ability to measure magnetization curves of individual magnetic atoms adsorbed on a nonmagnetic metallic substrate with use of a scanning tunneling microscope with a spin-polarized tip. We can map out low-energy magnetic interactions on the atomic scale as evidenced by the oscillating indirect exchange between a Co adatom and a nanowire on Pt(111). These results are important for the understanding of variations that are found in the magnetic properties of apparently identical adatoms because of different local environments.
283 citations
TL;DR: Results show that the Stoner-Wohlfarth model for single domain magnetization reversal via homogeneous rotation cannot explain experimental observations and in magnetosomes which are distinguished by nearly ideal crystallographic shapes and narrow size distribution large friction-like losses occur even for small field amplitude.
Abstract: For understanding hysteresis losses of magnetic nanoparticles to be used for magnetic particle hyperthermia the effect of size distribution on the dependence of hysteresis losses on magnetic field amplitude is studied on the basis of a phenomenological model in the size range from superparamagnetism to magnetic multi-domains—roughly 10 up to 100 nm. Relying on experimental data for the size dependence of coercivity, an empirical expression for the dependence of hysteresis loss on field amplitude and particle size is derived for hypothetical monodisperse particle ensembles. Considering experimentally observable size distributions, the dependence of loss on distribution parameters—mean particle size and variance—is studied. There, field amplitude is taken into account as an important parameter, which for technical and biomedical reasons in hyperthermia equipment is restricted. Experimental results for different particle types with mean diameter of 30 nm may be well reproduced theoretically if a small loss contribution of Rayleigh type is taken into account. Results show that the Stoner‐Wohlfarth model for single domain magnetization reversal via homogeneous rotation cannot explain experimental observations. In particular, in magnetosomes which are distinguished by nearly ideal crystallographic shapes and narrow size distribution large friction-like losses occur even for small field amplitude. Parameters of the high frequency field for hyperthermia (amplitude and frequency) as well as of the size distribution of applied particles are discussed with respect to attaining maximum specific heating power. (Some figures in this article are in colour only in the electronic version)
279 citations
TL;DR: The magnetization dynamics of a single domain ferromagnet in contact with a thermal bath is studied by scattering theory and the scattering theory for the Gilbert damping tensor is equivalent with the Kubo formalism.
Abstract: The magnetization dynamics of a single domain ferromagnet in contact with a thermal bath is studied by scattering theory. We recover the Landau-Liftshitz-Gilbert equation and express the effective fields and Gilbert damping tensor in terms of the scattering matrix. Dissipation of magnetic energy equals energy current pumped out of the system by the time-dependent magnetization, with separable spin-relaxation induced bulk and spin-pumping generated interface contributions. In linear response, our scattering theory for the Gilbert damping tensor is equivalent with the Kubo formalism.
128 citations
TL;DR: In this paper, single crystals of multiferroic BiFeO3 were investigated using neutron scattering, and the application of an electric field reversibly switches ferroelastic domains, inducing changes in the magnetic structure which follows rotation of the structural domains.
Abstract: Single crystals of multiferroic BiFeO3 were investigated using neutron scattering. Application of an electric field reversibly switches ferroelastic domains, inducing changes in the magnetic structure which follows rotation of the structural domains. In addition, electric fields can be used to control the populations of the equivalent magnetic domains within a single ferroelastic domain, possibly via field-induced strain.
110 citations
TL;DR: In this paper, hyperthermia measurements on a colloidal solution of 15 nm monodisperse FeCo nanoparticles (NPs) are reported, and the measured losses (1.5 mJ/g) compare to the highest of the literature, though the saturation magnetization of the NPs is well below the bulk one.
Abstract: We report on hyperthermia measurements on a colloidal solution of 15 nm monodisperse FeCo nanoparticles (NPs). Losses as a function of the magnetic field display a sharp increase followed by a plateau, which is what is expected for losses of ferromagnetic single-domain NPs. The frequency dependence of the coercive field is deduced from hyperthermia measurement and is in quantitative agreement with a simple model of non-interacting NPs. The measured losses (1.5 mJ/g) compare to the highest of the literature, though the saturation magnetization of the NPs is well below the bulk one.
109 citations
TL;DR: In this article, the results of X-ray diffraction measurements showed the M-type hexagonal structure of rare-earth substituted strontium ferrite nanopowders were prepared by sol-gel-autocombustion method and subsequent heat treatments.
99 citations
TL;DR: In this paper, the authors investigated the propagation of transverse domain walls in magnetic nanowires under axial and transverse magnetic fields using three-dimensional micromagnetic modeling.
Abstract: We have investigated the propagation of transverse domain walls in magnetic nanowires under axial and transverse magnetic fields using three-dimensional micromagnetic modeling. Transverse magnetic fields change the domain wall width and, below the Walker field, either increase or decrease the domain wall velocity depending when the field and wall magnetization are parallel or antiparallel, respectively. Furthermore, differences in the Walker field also appear for opposite transverse fields, and a surprising result is that under relatively high axial and transverse fields, Walker breakdown can be completely suppressed and the domain wall velocity returns to several hundreds of ms−1.
91 citations
TL;DR: In this paper, the stripe domain patterns of a uniaxial magnetic film in the superconducting/ferromagnetic hybrid were used to induce anisotropic vortex pinning and manipulating the directional motion of vortices.
Abstract: We demonstrate a unique prospect for inducing anisotropic vortex pinning and manipulating the directional motion of vortices by using the stripe domain patterns of a uniaxial magnetic film in the superconducting/ferromagnetic hybrid. Our observations can be described by a model, which considers interactions between magnetic charges of vortices and surface magnetic charges of domains resulting in the enhanced pinning of vortices on domain walls.
89 citations
TL;DR: High-field magnetization and magnetostriction measurements on the rare-earth-metal tetraboride TbB4, in which the Tb moments form a Shastry-Sutherland lattice in the tetragonal basal plane, are reported.
Abstract: We report high-field magnetization and magnetostriction measurements on the rare-earth-metal tetraboride TbB4, in which the Tb moments form a Shastry-Sutherland lattice in the tetragonal basal plane. A number of magnetization plateaus appear when the magnetic field is perpendicular to the magnetic easy plane. We propose that the magnetization plateaus arise from the combined effect of magnetic frustration and quadrupole interaction in the unique two-dimensional network.
TL;DR: In this paper, the fabrication of highly crystalline magnetite particles with a uniform morphology and a relatively uniform average size of 54 nm was described, which were fabricated by oxidation of Fe(OH)2 by nitrate in basic aqueous media.
Abstract: We report the fabrication of highly crystalline magnetite particles with a uniform morphology and a relatively uniform average size of 54 nm. Particles were fabricated by oxidation of Fe(OH)2 by nitrate in basic aqueous media. Characterization of the particles by means of transmission electron microscopy, Raman spectroscopy, X-ray and electron diffraction, and magnetometry showed that they were octahedral magnetic monodomains of highly stoichiometric magnetite (unit formula was estimated to be Fe2.985O4), with room-temperature ferrimagnetic behavior and a saturation magnetization of 81.6 emu/g.
TL;DR: The first direct observation of current-driven domain wall motion in a CoCrPt wire with perpendicular magnetic anisotropy was reported in this article, where a single DW introduced in the wire is displaced back and forth by positive and negative pulsed current.
Abstract: We report the direct observation of current-driven domain wall (DW) motion in a CoCrPt wire with perpendicular magnetic anisotropy. Magnetic force microscopy showed that a single DW introduced in the wire is displaced back and forth by positive and negative pulsed current. This is the first demonstration of the current-driven DW motion in a metallic magnetic wire with perpendicular magnetic anisotropy in the absence of a magnetic field.
TL;DR: A novel doubly chiral magnetic order is found in the structurally chiral langasite compound Ba3NbFe3Si2O14 and it is proved that a single triangular chirality together with a single helicity is stabilized in an enantiopure crystal.
Abstract: A novel doubly chiral magnetic order is found out in the structurally chiral langasite compound Ba$_3$NbFe$_3$Si$_2$O$_{14}$. The magnetic moments are distributed over planar frustrated triangular lattices of triangle units. On each of these they form the same triangular configuration. This ferro-chiral arrangement is helically modulated from plane to plane. Unpolarized neutron scattering on a single crystal associated with spherical neutron polarimetry proved that a single triangular chirality together with a single helicity is stabilized in an enantiopure crystal. A mean field analysis allows discerning the relevance on this selection of a twist in the plane to plane supersuperexchange paths.
TL;DR: In this paper, noncollinear uniaxial and unidirectional exchange anisotropy contributions are discovered and identified as a cause of loop asymmetry in exchange-coupled ferromagnetic/antiferromagnetic thin films Adjusting the magnetic reversal field axis to compensate for the tilted anisotropies eliminates the loop and magnetic domain reversal asymmetry.
Abstract: Noncollinear uniaxial and unidirectional exchange anisotropy contributions are discovered and identified as a cause of loop asymmetry in exchange-coupled ferromagnetic/antiferromagnetic thin films Adjusting the magnetic reversal field axis to compensate for the tilted anisotropies eliminates the loop and magnetic domain reversal asymmetry The deviation from collinearity of exchange coupling is suggested to originate from antiferromagnetic-layer-induced interfacial magnetic frustration The effects are independent of the occurrence of exchange bias, existing below and above the onset of exchange bias The additional anisotropy contributions add another mechanism to the occurrence of exchange coupling
TL;DR: The magnetization behavior and the domain pattern in remanence are studied in Co/Pt multilayers and it is revealed that the magnetization canting is such that all in-plane orientations of magnetization are equally occupied.
Abstract: The magnetization behavior and the domain pattern in remanence are studied in Co/Pt multilayers. The reorientation of magnetization from perpendicular to in plane is found to happen via the state of canted magnetization. In the transition from an easy axis to an easy plane a stable domain pattern in the in-plane magnetization components is found for Co/Pt multilayers. The analysis of the domain pattern reveals that the magnetization canting is such that all in-plane orientations of magnetization are equally occupied. The found structure is appointed to the cone state.
TL;DR: In this paper, the spectrum of absorbed power as probed by ferromagnetic resonance (FMR) is numerically calculated within a macro-spin model for single domain nanoparticles using Landau-Lifshitz-Gilbert dynamics.
TL;DR: By applying a rotating magnetic field on the nematic phase, the bend-splay Frederiks transition is observed, visible as a spatially periodic transient pattern with a wavelength that depends on sample thickness and field strength.
Abstract: We report on a study of the influence of a magnetic field on the nematic phase and the isotropic-to-nematic (IN) phase transition of hard colloidal gibbsite platelets. We find direct visual evidence of a shift of the IN transition to lower concentrations due to the magnetic field. The nematic phase readily aligns when contained between two parallel flat glass walls, with homeotropic orientation. This well-defined surface anchoring enables a measurement of the bend Frederiks transition, yielding the bend elastic constant of a nematic phase of hard disks as K(3) = 7 x 10(-14) N . By applying a rotating magnetic field on the nematic phase, we observe the bend-splay Frederiks transition, visible as a spatially periodic transient pattern with a wavelength that depends on sample thickness and field strength. Following a linear stability analysis we are able to account for this dependence in a qualitative way. Moreover, the rotating magnetic field enables us to render the nematic phase single domain, with well-defined director orientation.
TL;DR: In this paper, an analytical and computational study of 360° domain walls in thin uniaxial ferromagnetic films is presented, and the existence of stable one-dimensional 360°-domain wall solutions both with and without the applied field is demonstrated in a reduced thin film micromagnetic model.
Abstract: An analytical and computational study of 360° domain walls in thin uniaxial ferromagnetic films is presented. The existence of stable one-dimensional 360° domain wall solutions both with and without the applied field is demonstrated in a reduced thin film micromagnetic model. The wall energy is found to depend rather strongly on the orientation of the wall and the wall width significantly grows when the strength of the magnetostatic forces increases. It is also shown that a critical reverse field is required to break up a 360° domain wall into a pair of 180° walls. The stability of the 360° walls in two-dimensional films of finite extent is demonstrated numerically and the stability with respect to slow modulations in extended films is demonstrated analytically. These domain wall solutions are shown to play an important role in magnetization reversal. In particular, it is found that the presence of 360° domain walls may result in nonuniqueness of the observed magnetization patterns during repeated cycles ...
TL;DR: In this article, the authors investigated the effect of magnetic reversal in graded magnetic-recording media and its effect on the areal density, and showed that the write-field reduction negatively affects the amortization ratio, and there remains a trade-off between write field and bit size.
Abstract: Magnetization reversal in graded magnetic-recording media and its effect on the areal density are investigated by model calculations. By choosing suitable solid-solution materials it is conceptually straightforward, though practically challenging, to achieve arbitrarily low write fields. The writing process involves both the nucleation of reverse domains and their propagation along elongated particles. The performance of the medium is optimized for pinning and nucleation fields of comparable size, and the two fields can be tuned by adjusting the length of the elongated particles (pillars) and the anisotropies of the hard and soft ends. However, the write-field reduction negatively affects the areal density, and there remains a trade-off between write field and bit size.
TL;DR: Using microwave currents, the resonance frequency of the domain wall oscillator can be tuned over a wide range, and the quantitative shape of the potential is deduced, so that a complete characterization of the pinning potential is obtained.
Abstract: Using microwave currents, we excite resonances of geometrically confined pinned domain walls, detecting the resonance by the rectification of the microwave current. By applying magnetic fields, the resonance frequency of the domain wall oscillator can be tuned over a wide range. Increasing the power leads to a redshift due to the nonlinearity of the system. From this frequency shift, we directly deduce the quantitative shape of the potential, so that a complete characterization of the pinning potential is obtained.
TL;DR: In this paper, a coupled two-equation system was proposed to predict the permeability tensor behavior of polycrystalline ferrites regardless of their magnetization state, and the results were compared with those for existing models for various magnetized states.
Abstract: We describe a theoretical approach for determining the permeability tensor of polycrystalline ferrites regardless of their magnetization state. To take into account both the demagnetizing dynamic fields related to the magnetic domain and grain shapes and the magnetic interactions between adjoining domains and between adjoining grains, we transform the classical Landau-Lifschitz-Gilbert equation into a coupled two-equation system. We introduce statistical distribution laws for both the domain and grain demagnetizing coefficients into the calculation to take the domain and grain shape diversity into account and derive static vectorial quantities such as the internal magnetic dc field and magnetization in each domain that depends on the applied dc magnetic field from the Stoner-Wohlfarth hysteresis model. We compare results with those for existing models for various magnetized states. Then we apply the model to predict the permeability tensor behavior of barium hexaferrite thin film, especially in the remanent state, which is of great interest for the design of self-biased Y-junction circulators in the millimeter-wave range.
TL;DR: In this article, Coombs et al. proposed a method to magnetize a superconductor in the presence of a solenoid, which can be switched on and off.
Abstract: The potential of bulk melt-processed YBCO single domains to trap significant magnetic fields (Tomita and Murakami 2003 Nature 421 517–20; Fuchs et al 2000 Appl. Phys. Lett. 76 2107–9) at cryogenic temperatures makes them particularly attractive for a variety of engineering applications including superconducting magnets, magnetic bearings and motors (Coombs et al 1999 IEEE Trans. Appl. Supercond. 9 968–71; Coombs et al 2005 IEEE Trans. Appl. Supercond. 15 2312–5). It has already been shown that large fields can be obtained in single domain samples at 77 K. A range of possible applications exist in the design of high power density electric motors (Jiang et al 2006 Supercond. Sci. Technol. 19 1164–8). Before such devices can be created a major problem needs to be overcome. Even though all of these devices use a superconductor in the role of a permanent magnet and even though the superconductor can trap potentially huge magnetic fields (greater than 10 T) the problem is how to induce the magnetic fields. There are four possible known methods: (1) cooling in field; (2) zero field cooling, followed by slowly applied field; (3) pulse magnetization; (4) flux pumping. Any of these methods could be used to magnetize the superconductor and this may be done either in situ or ex situ. Ideally the superconductors are magnetized in situ. There are several reasons for this: first, if the superconductors should become demagnetized through (i) flux creep, (ii) repeatedly applied perpendicular fields (Vanderbemden et al 2007 Phys. Rev. B 75 (17)) or (iii) by loss of cooling then they may be re-magnetized without the need to disassemble the machine; secondly, there are difficulties with handling very strongly magnetized material at cryogenic temperatures when assembling the machine; thirdly, ex situ methods would require the machine to be assembled both cold and pre-magnetized and would offer significant design difficulties. Until room temperature superconductors can be prepared, the most efficient design of machine will therefore be one in which an in situ magnetizing fixture is included. The first three methods all require a solenoid which can be switched on and off. In the first method an applied magnetic field is required equal to the required magnetic field, whilst the second and third approaches require fields at least two times greater. The final method, however, offers significant advantages since it achieves the final required field by repeated applications of a small field and can utilize a permanent magnet (Coombs 2007 British Patent GB2431519 granted 2007-09-26). If we wish to pulse a field using, say, a 10 T magnet to magnetize a 30 mm × 10 mm sample then we can work out how big the solenoid needs to be. If it were possible to wind an appropriate coil using YBCO tape then, assuming an Ic of 70 A and a thickness of 100 µm, we would have 100 turns and 7000 A turns. This would produce a B field of approximately 7000/(20 × 10−3) × 4π × 10−7 = 0.4 T. To produce 10 T would require pulsing to 1400 A! An alternative calculation would be to assume a Jc of say 5 × 108A m−1 and a coil 1 cm2 in cross section. The field would then be 5 × 108 × 10−2 × (2 × 4π × 10−7) = 10 T. Clearly if the magnetization fixture is not to occupy more room than the puck itself then a very high activation current would be required and either constraint makes in situ magnetization a very difficult proposition. What is required for in situ magnetization is a magnetization method in which a relatively small field of the order of millitesla repeatedly applied is used to magnetize the superconductor. This paper describes a novel method for achieving this.
TL;DR: In this article, the magnetically coupled superconductor-ferromagnet bilayer is studied and the authors demonstrate a prominent difference in critical current density between cases when magnetic domain stripes are oriented parallel and perpendicular to the superconducting current, which is related to the matching periodicities of the Abrikosov vortex lattice and the magnetic stripe domains.
Abstract: We study the magnetically coupled superconductor-ferromagnet bilayers comprised of a ferromagnet with a rotatable periodic stripelike magnetic domain structure with alternating out-of-plane component of magnetization and a MoGe superconductor. We demonstrate a prominent difference in critical current density between cases when magnetic domain stripes are oriented parallel and perpendicular to the superconducting current. The bilayer exhibits pronounced commensurability features that are related to the matching periodicities of the Abrikosov vortex lattice and the magnetic stripe domains.
TL;DR: In this article, the steady state behavior and magnetization switching process of single domain particles subject to ac and dc magnetic fields using analytical and numerical models based on the Landau-Lifshitz-Gilbert equation was studied.
Abstract: We studied the steady state behavior and magnetization switching process of single domain particles subject to ac and dc magnetic fields using analytical and numerical models based on the Landau–Lifshitz–Gilbert equation. We compared the analytical solutions for circularly polarized fields with a numerical single spin model and circularly and linearly polarized ac magnetic fields. It has been found, that the initial conditions and the dynamics of the external fields (field ramps and amplitude changes) strongly determine which precession orbit the magnetization converges to, if the magnetization precession is stable, and if the magnetization switches. We also studied the effects of field amplitudes, field angles, and damping on the switching behavior. The presented results can be applied to high power ferromagnetic resonance experiments and ferromagnetic resonance assisted magnetic recording schemes.
TL;DR: The micromagnetics simulation reveals that the domain wall motion in the wire with finite roughness causes the dynamical pinning due to the Walker breakdown, which semiquantitatively explains the experimental results.
Abstract: Transmission probability of a domain wall through a magnetic nanowire is investigated as a function of the external magnetic field. A very intriguing phenomenon is found that the transmission probability shows a significant drop after exceeding the threshold driving field, which contradicts our intuition that a domain wall is more mobile in the higher magnetic field. The micromagnetics simulation reveals that the domain wall motion in the wire with finite roughness causes the dynamical pinning due to the Walker breakdown, which semiquantitatively explains our experimental results.
TL;DR: In this paper, the implant assisted magnetic targeted drug delivery system of Aviles, Ebner and Ritter is considered, where large ferromagnetic particles are implanted as seeds to aid collection of multiple domain nanoparticles (radius ).
TL;DR: In this article, the orthorhombic phase of YMnO3 has been epitaxially stabilized on single crystal substrates and the out-of-plane orientation of the epitaxial films can be tuned to (001), (101), or (100).
TL;DR: In this article, the superparamagnetic blocking temperature at low applied field of 0.005 T was shown to be around 125 K, at higher applied field, these ZFC and FC magnetization curves merged because of increase in magnetization energy that overcomes the magnetic anisotropy and dipolar interaction energies.
TL;DR: Detailed magnetic properties of the compound Sr(2)YbRuO(6) are presented here, revealing clear evidence for two components of magnetic ordering aligned opposite to each other, leading to a magnetization reversal, compensation temperature and negative magnetization at low temperatures and low magnetic fields.
Abstract: Detailed magnetic properties of the compound Sr2YbRuO6 are presented here. The compound belongs to the family of double perovskites forming a monoclinic structure. Magnetization measurements reveal clear evidence for two components of magnetic ordering aligned opposite to each other, leading to a magnetization reversal, compensation temperature (T* = 34 K) and negative magnetization at low temperatures and low magnetic fields. Heat capacity measurements corroborate the presence of two components in the magnetic ordering and a noticeable third anomaly at low temperatures (~15 K) which cannot be attributed the Schottky effect. The calculated magnetic entropy is substantially lower than that expected for the ground states of the ordered moments of Ru5+ and Yb3+, indicating the presence of large crystal field effects and/or incomplete magnetic ordering and/or magnetic frustrations well above the magnetic ordering. An attempt is made to explain the magnetization reversal within the frameworks of available models.