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In this paper we show that magnetostatic models of permanent magnets, based on distributions of magnetic charge and shaped by a helicoidal geometry of cylindrical type, have the volume charge density ρM equal to zero. This result is valid when (i) the modulus of the vector physical magnetization density M has a constant value in all the points of the helicoidal magnet and (ii) M has the same direction of an oriented straight line having a constant angle with respect to the normal line of a cylindrical helix. Another case study concerns the permanent magnets with conchospiral geometry and magnetization M. For this kind of magnet we show that, in general, ρM≠0. Furthermore, in relation to the nonobvious result ρM=0 obtained for the cylindrical helicoidal permanent magnets, some geometrical physical considerations are illustrated. With reference to these observations, in order to understand if ρM is equal to zero or not without considering divergence computation, the possibility of defining a criterion based only on the geometry and magnetization of the magnet is discussed. Finally, an application of the results obtained from the previous analysis is shown. After drawing an analytical formulation of the surface charge density σM relative to a cylindrical helicoidal magnet, a complete evaluation of the field distribution around this magnet is performed. The results are presented by using cylindrical polar graphics of the magnetic flux B. [ABSTRACT FROM AUTHOR]

The paper presents resistivity and magnetization measurements on nearly stoichiometric Fe3Si films epitaxially grown on GaAs substrates by electron-beam evaporation in an ultrahigh vacuum chamber. In the low-temperature resistivity a T3 term was found in all samples. A term like that is known to describe the anomalous single-magnon scattering processes in half-metallic materials and confirms so for our samples the hypothesis of half-metallic ferromagnetism in Fe3Si. The films show an anisotropic magnetoresistance in low magnetic fields. In high magnetic fields a negative longitudinal and transverse magnetoresistance (MR) has been observed linearly depending on the field strength. In the vicinity of 200 K the MR shows maximum absolute values up to 1.5% at magnetic fields of about 8 T. From the magnetization measurements a magnetic moment of 0.86μB/atom was obtained, which is close to that of bulk Fe3Si. [ABSTRACT FROM AUTHOR]

We present in this paper the changes in the room temperature magnetic property of ZnO on Mn doping prepared using solvothermal process. The zero field cooled (ZFC) and field cooled (FC) magnetization of undoped ZnO showed bifurcation and magnetic hysteresis at room temperature. Upon Mn doping the magnetic hysteresis at room temperature and the bifurcation in ZFC-FC magnetization vanish. The results seem to indicate that undoped ZnO is ferromagnetic while on the other hand the Mn doped ZnO is not a ferromagnetic system. We observe that on addition of Mn atoms the system shows antiferromagnetism with very giant magnetic moments. [ABSTRACT FROM AUTHOR]

In recent years, magnetic levitation is finding interesting applications in various fields related to microdevices. Producing inexpensive microfabricated magnetic films is of high importance to all magnetically levitated microdevices. This paper introduces a microlevitation system and presents the fabrication of Co–Ni–Mn–P films using electrodeposition. The fabrication parameters are varied such that magnetization direction of the film is varied by changing the crystal structure. The magnetic properties of the films such as coercivity, remanence, and maximum energy product demonstrate that hexagonal structure promotes out-of-plane magnetization whereas cubic structure reinforces in-plane magnetization. The performance of the Co–Ni–Mn–P films is evaluated by magnetic levitation experiments of silicon samples. Satisfactory results are obtained toward the goal of realization of a magnetically levitated microgripper. [ABSTRACT FROM AUTHOR]

In this paper the magnetization decay behavior of neutron irradiated MgB2 bulk samples and an estimate of the strength of the introduced pinning centers are presented. The magnetization decay measurements appear much more complex than usual, in fact, they may be logarithmic or not, depending on the values of temperature and magnetic field and, as the region of low temperatures and fields is approached, they are affected by a “noise” that is out of experimental uncertainties. This “noisy” behavior is attributed to the small flux jumps, related to the dendritic flux penetration, widely observed in MgB2 samples. We identify a phase diagram that divides the H-T plane in two regions: one, at relatively low temperatures and fields, where the decay observed is noisy, the other, outside it, where the decay is “clean.” This noisy region extends up to T/Tc≅0.5 and up to a field of some teslas, i.e., in a range of instability much more extended than that found in previous measurements. At high magnetic field the pinning energy turns out to be higher in irradiated samples than in the pristine one, in agreement with the observed increase in the critical current density. However, at high enough fields and temperatures, pinning is no longer effective and, by varying the measurement frequency, differences in the magnetic valuation of critical current density are observed. This fact may be of importance because it occurs at magnetic field and temperature conditions where technological applications of MgB2 are expected. [ABSTRACT FROM AUTHOR]

We present a detailed numerical simulation study of the effects caused by the magnetodipolar interaction between ferromagnetic (FM) layers of a trilayer magnetic nanoelement on its magnetization dynamics. As an example, we use a Co/Cu/Ni80Fe20 element with a square lateral shape where the magnetization of FM layers forms a closed Landau-like domain pattern. First, we show that when the thickness of the nonmagnetic (NM) spacer is in the technology relevant region h∼10 nm, magnetodipolar interaction between 90° Neel domain walls in FM layers qualitatively changes the equilibrium magnetization state of these layers. In the main part of the paper, we compare the magnetization dynamics induced by a sub-nsec field pulse in a single-layer Ni80Fe20 (Py) element and in the Co/Cu/Py trilayer element. Here, we show that (i) due to the spontaneous symmetry breaking of the Landau state in the FM/NM/FM trilayer, its domains and domain walls oscillate with different frequencies and have different spatial oscillation patterns; (ii) magnetization oscillations of the trilayer domains are strongly suppressed due to different oscillation frequencies of domains in Co and Py; (iii) magnetization dynamics qualitatively depends on the relative rotation sense of magnetization states in Co and Py layers and on the magnetocrystalline anisotropy kind of Co crystallites. Finally, we discuss the relation of our findings with experimental observations of magnetization dynamics in magnetic trilayers, performed using the element-specific time-resolved x-ray microscopy. [ABSTRACT FROM AUTHOR]

In this paper we have investigated the effect of nanometric grain size modulation on the behavior of magnetoimpedance (MI), magnetoresistance, and magnetic properties of a series of single-phase nanocrystalline colossal magnetoresistance La0.7Sr0.3MnO3 (LSMO) manganites all synthesized through chemical route “pyrophoric reaction process.” MI measurements were carried out at room temperature (T=300 K) in the ac signal frequency (f) range of 40 kHz-110 MHz and in dc magnetic field (H) range of -2.5 kOeC=360 K. For comparison, we have also presented room temperature low-field magnetoresistance (LFMR) study of this series of LSMO nanoparticles. This study reveals that within this particle size range, 14–28 nm, LFMR decreases with decrease in particle size, which in fact mimics the variation of MI with particle size. [ABSTRACT FROM AUTHOR]

The high temperature magnetization behavior of an air sintered nanocrystalline ZnO:Co (5 at. %) sample while it is subjected to thermal cycles in vacuum/air ambient is reported in the present paper. The pristine air sintered sample exhibits intrinsic room temperature ferromagnetism. Upon vacuum annealing, the magnetization of this sample increases significantly and the sample remains ferromagnetic up to 630 °C. This has been attributed to the formation of Co clusters, and thus, the ferromagnetic ordering is extrinsic in nature. The subsequent air annealing of the vacuum annealed ZnO:Co (5 at. %) sample, however, reverts back the magnetization to a value that was observed in the pristine air sintered sample. This is due to complete oxidation of the cobalt clusters. Furthermore, the sample’s magnetization at room temperature and also its temperature dependence up to 630 °C remain unaffected by further annealing in vacuum or air, a feature required of a material for its device applications. The Curie temperature of this robust sample is ∼450 °C. [ABSTRACT FROM AUTHOR]

This paper presents results of micromagnetic simulations of magnetization switching driven by spin-polarized current in magnetic tunnel junctions. For the studied structures, and for all the simulated currents, the switching occurs via nucleation process. A complete study of how a misalignment of the applied field and nonidealities in the shape of the sample affect the switching behavior has also been performed. The main results are as follows: (a) The switching mechanism does not change qualitatively by introducing a misalignment and (b) In contrast, the switching mechanism changes qualitatively when a nonideal shape is introduced. Lastly, simulations that include the effects of a 77 K thermal bath are presented; these indicate that the switching times are shorter than for zero temperature simulations (sometimes also less than 50%). [ABSTRACT FROM AUTHOR]

In this paper we present an experimental investigation of the nonlinear microwave properties of coplanar resonators patterned from epitaxial Y1Ba2Cu3O7-δ thin films in zero-field-cooled, field-cooled, and field-sweep experiments in the search for the fundamental limiting mechanism. The impact of magnetization, vortices, intrinsic limitation, grain boundaries, and thermal effects is evaluated. We find that the fundamental limiting mechanism in the absence of thermal and grain-boundary effects is given by the dc critical current density of the superconducting material which masks the intrinsic limitation expected at larger rf current densities. Demagnetizing effects, penetration barriers, vortex penetration, pinning, and relaxation of inhomogeneous vortex distributions are experimentally observed and in agreement with theoretical expectations. The experimental results are modeled in terms of a simple model for the power-handling capability which is based on a superposition of all current densities in the resonator and gives a consistent explanation of all experiments in magnetic fields and in zero field. [ABSTRACT FROM AUTHOR]

This paper describes a method for evaluating the magnetization-induced element in a third-order nonlinear optical susceptibility tensor. One difficulty in estimating this element is that the Faraday effects at fundamental and harmonic wavelengths are entangled with the polarization state of the outgoing harmonic wave. Using our method, the contribution of the Faraday effects can be isolated and removed from the rotation angle and the ellipticity of the outgoing harmonic wave. The theoretical expressions for the right- and left-handed circularly polarized components of the outgoing harmonic wave from magnetic media are derived. A formula for evaluating the magnetization-induced element is then determined from these expressions. Applying this formula to a bismuth-aluminum-doped yttrium-iron garnet thin film gives the magnetization-induced element |χxyyy(3),m|=4×10-21 m2/V2 at the fundamental wave of 1.17 eV (third-harmonic wave: 3.50 eV) in a magnetic field of +1 kOe. [ABSTRACT FROM AUTHOR]

Magnetic shape memory (MSM) materials change their shape with the magnetic field. They can also be used in the reverse operation as sensors or voltage generators. The present paper demonstrates that large voltages are induced when the MSM material is mechanically compressed inside a MSM actuator. The experimental results reveal that voltages of close to 100 V were generated with a Ni–Mn–Ga MSM material subjected to short mechanical impulses, because of a change in its magnetization. The induced voltage depends on the geometrical and material parameters of the MSM actuator, as well as on the speed by which the MSM material changes its shape. A magnetic model for calculating the induced voltage is proposed and the measurement results from a MSM-type actuator are presented. The magnetic model demonstrates good accordance with the experimental results. The physical reason for the voltage signal is discussed and potential applications are proposed. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A model is introduced in this paper to describe the effects of thermal magnetic noises in the read sensor under off-track reading conditions taking into account the influence of the magnetic field generated by the recorded magnetization patterns on the medium. Our numerical studies show that there exist additional noises in the hard biased reader, depending on recorded patterns on the magnetic media. The influence of the recorded magnetic patterns is not only on the variation in reader resistance but also on the high frequency noises caused primarily by the thermal fluctuations. The theoretical analysis is based on the micromagnetic modeling of the state of magnetization in read sensor taking into account of its external magnetic fields due to both the hard bias and the media magnetization patterns. The effect of the thermal agitation of the gyromagnetical precession of magnetizations is evaluated by considering the angular magnetic noise. [ABSTRACT FROM AUTHOR]

The Stoner–Wohlfarth model is a classical model for magnetic hysteresis of single-domain magnets. For two-dimensional (2D) magnets at finite temperatures, the Stoner–Wohlfarth model must be extended to include intrinsic strong spin fluctuations. We predict several fundamentally different hysteresis properties between 2D and 3D magnets. The magnetization switching diagram known as the astroid figure in the conventional Stoner–Wohlfarth model becomes highly temperature dependent and asymmetric with respect to the transverse and longitudinal magnetic fields. Our results provide new insights into the spintronics applications based on 2D magnetic materials. [ABSTRACT FROM AUTHOR]

A giant magnetoresistance (GMR) sensor with a Wheatstone bridge structure and an out-of-plane linear response was developed. The spin-valve structure consists of a synthetic antiferromagnetic [(Co/Pt)n/Ru/(Pt/Co)n] reference layer with perpendicular magnetic anisotropy, a Cu spacer layer, and a Co-free layer with in-plane easy magnetization. By utilizing the spin–orbit torque induced magnetization switching in the synthetic antiferromagnetic layer, the magnetization of the reference layers in the adjacent bridge arms is set to the opposite direction, achieving a GMR sensor with a full Wheatstone bridge structure. The sensor exhibits linear response to the out-of-plane magnetic field with adjustable dynamic ranges from hundreds to thousands of Oe, depending on the thickness of the Co-free layer. A similar Wheatstone bridge sensor consisting of magnetic tunnel junctions was also proposed. The sensor with out-of-plane linear response may have promising applications in three-dimensional magnetic field detection and current sensing field. [ABSTRACT FROM AUTHOR]

Spintronic devices would greatly benefit from a noncollinear alignment between magnetizations of adjacent ferromagnetic layers for maximum performance and reliability. We demonstrate that such an alignment can be created and controlled by coupling two ferromagnetic layers across a magnetic spacer layer consisting of a nonmagnetic material, Ru, alloyed with a ferromagnetic element, Co. Changing the composition and thickness of the spacer layer enables the control of the relative angle between the magnetizations of the ferromagnetic layers between 0 ° and 180 °. The onset of noncollinear alignment between the ferromagnetic layers coincides with the advent of magnetic order in the spacer layer. This study maps the concentration and thickness ranges of RuCo spacer layers that give rise to noncollinearity between ferromagnetic Co layers. The experimental results are successfully reproduced by simulating our structures with an atomistic model. This model assumes that Co atoms in the RuCo spacer layer have magnetic moments and that neighboring Co atoms are ferromagnetically coupled, while Co atoms separated by one or more Ru atoms are antiferromagnetically coupled. [ABSTRACT FROM AUTHOR]

Half-metallic Heusler alloys are receiving significant attention for spintronic applications utilizing magnetic tunnel junctions and requiring large spin polarization. Co2MnSi (CMS) is one of the most promising candidates for this purpose. Here, we report the magnetization dynamics of a thin, epitaxial CMS film in a magnetic CoFe/CMS bilayer structure sputtered on an MgO substrate. The magnetic precession frequency response of the CoFe/CMS bilayer shows a fourfold symmetry with respect to the azimuthal applied field angle, reflecting the crystal symmetry of the CMS layer and not the underlying CoFe film. Moreover, the effective Gilbert damping parameter exhibits inhomogeneous broadening at lower applied magnetic fields. At large fields, however, the azimuthal angle dependence disappears, and the intrinsic Gilbert damping is observed. This study provides insight into the dynamics of a magnetic bilayer structure that forms an integral element in spintronic applications. [ABSTRACT FROM AUTHOR]

Presents a study that developed a numerical analysis method for the magnetization in magnetoresistive sensors. Details of the method; Examination of the changes in total magnetization for the magnetoresistive sensor; Analysis of the magnetization distributions in the magnetoresistive sensor.

This paper presents a numerical model for the study of micro-Hall magnetometry applications, aiming at evaluating the sensitivity of semiconductor miniaturized devices to the stray field of permalloy nanostructures with ring and disk geometry. The procedure couples a micromagnetic code, for the calculation of the stray field generated by the nanomagnet, to a 2D classical transport model for the determination of the electric potential distribution inside the Hall plate. The model is applied to study the sensitivity of a micro-Hall device in the detection of magnetization switching processes characterized by vortex state, focusing on the influence of magnetic nanostructure position. [ABSTRACT FROM AUTHOR]

The usual skin effect observed in magnetically linear medium (l = const.) is absent in a magnetically non-linear medium, leading to wrong predictions of the eddy current field using the classical approach. For this reason, this paper proposes a thin sheet model, improving the eddy current field description on the basis of physical ideas in the framework of the saturation wave model, which describes the dynamic magnetization of the material with rectangular hysteresis loop. Therewith, the layer-to-layer nature of the magnetization reversal is taken into account. The hysteresis is modeled by means of a static history-dependent hysteresis model. This leads to a simplified model of conducting ferromagnetic sheet, which describes magnetization of isotropic electrical steels. [ABSTRACT FROM AUTHOR]

In this paper, a novel numerical time-stepping scheme for the solution of the dynamic Landau- Lifshitz equation of micromagnetics is introduced. The equation is a non-linear problem, and is traditionally solved using semi-discretization techniques. However, these techniques corrupt some intrinsic properties of the Landau-Lifshitz (LL) dynamics such as the conservation of magnetization magnitude in time. The proposed approach uses a mixed mid-point Runge-Kutta like algorithm which satisfies LL dynamic properties for time-steps up to 1.25 ps. The accuracy of the proposed scheme has been tested and verified using lmag Standard Problem 4 against popular micromagnetic simulation software for different time-steps and cell sizes. [ABSTRACT FROM AUTHOR]

Spin torque majority gate (STMG) is one of the promising options for beyond complementary metaloxide- semiconductor logic. Improvement of its performance-switching speed vs. required current- is critical for its competitiveness. In this paper, (a) we identify an optimized layout of the gate comprised of thin magnetic wires with in-plane magnetization; (b) we optimize geometries of perpendicular magnetization spin torque majority gates. Micromagnetic simulations demonstrate an improvement in switching current for in-plane magnetization (with less than 1 ns switching time) from 6mA in the original scheme to 1.5mA in the present one. Additionally, failures of switching caused by vortex formation are eliminated and desired output magnetization is achieved. Various geometries of STMG with perpendicular magnetization are explored. The scheme with a straight cross proves to be the most advantageous. It is predicted to operate with the switching current of 50 lA and less than 4 ns switching time. [ABSTRACT FROM AUTHOR]

In this paper, we studied the critical diameter of superparamagnetic core-shell particles. One pot method and microwave-assisted technique were used to synthesize Ag-Ni core-shell nanoparticles with diameters of 10 nm and 30nm. From the experimental results of hysteresis (M-H curves) and temperature dependent magnetization (M-T curves), the theoretical critical diameter does not agree with the experimental observation of the core-shell structure. Furthermore, the blocking temperature equation should be reconsidered. [ABSTRACT FROM AUTHOR]

α"-Fe16N2 has been suggested as a promising candidate for future rare-earth-free magnets. In this paper, we report to use high magnetic field (9 T) assisted post-annealing process to enhance the Fe16N2 phase formation in FeN bulk rod samples during the α" → α" phase transformation and thus improve its magnetic properties. It was found by X-ray Diffraction measurement that the volume ratio of Fe16N2 phase was increased up to 22%, which corresponds to an increase in the amount of transformation from α" → α" up to 78%. Also, the saturation magnetization (Ms) of the prepared FeN rod sample was increased to 227 emu/g with its coercivity up to 376 Oe at room temperature. A working mechanism for the high field assisted post-annealing process was presented. [ABSTRACT FROM AUTHOR]

This paper reports morphology, structure, and magnetic properties of air-stable soft magnetic FexCo100-x (x=65, 50, and 34) and Fe50Ni50 (at. %) submicron and nanosize particles fabricated by template-free thermal decomposition of nitrates of Fe, Co, and Ni and subsequent hydrogen reduction. The particle compositions were tuned by modification of the precursor solution concentrations. The as-synthesized Fe-Co and Fe50Ni50 particles have body centered cubic and face centered cubic poly-nanocrystalline structures, respectively. The Fe-Co and Fe50Ni50 particles have particle sizes in the range of 28-200 nm and 70-480 nm, and average grain sizes of 16-29 nm and 20-24 nm, respectively. The particle and grain sizes were controlled by tuning particle composition, and the temperature and time of hydrogen reduction. Saturation magnetization Ms as high as 207-224 emu/g and intrinsic coercivity Hci of 59-228 Oe were obtained in the Fe-Co particles reduced at 550 °C for 90 min. Of special note, the Ms of 224 emu/g (∼2.3 T) obtained in the Fe65Co35 particles is among the highest values for Fe-Co particles reported so far. Ms of 135-137 emu/g and Hci of 59-111 Oe were obtained in the Fe50Ni50 particles reduced at 500 or 550 °C for 20 min. [ABSTRACT FROM AUTHOR]

The characterization of magnetic memory effect is the primary task of the metal magnetic memory (MMM) technique used in quantitative evaluation, and it has been characterized by the Jiles-Atherton (J-A) model in recent papers. The feasibility of using the MMM field to characterize magnetization intensity M and the feasibility of using the J-A model in MMM detection are discussed in this paper to clarify the magnetic memory effect in the elastic stage. According to analysis with the J-A model and the results of a rotating bending fatigue experiment, the MMM field follows the law that the state approaches equilibrium under the action of cyclic stress. This is similar to what the J-A model shows, only with replacement of the global equilibrium state Man in the J-A model with the local equilibrium state M0. The expression of M0 is obtained by considering the energy balance in the process of magnetization. M0 changes with the pinning resistance, external field, and type of stress cycle. Additionally, the M0-σ curve is a loop around the Man-σ curve, which is consistent with experimental results. How the modified J-A model describes the variation in MMM field in the process of fatigue is also discussed. This paper shows that the J-A model can be used to analyze the magnetic memory effect in the process of fatigue after replacing Man with M0. [ABSTRACT FROM AUTHOR]

Measuring the similarity between materials is essential for estimating their properties and revealing the associated physical mechanisms. However, current methods for measuring the similarity between materials rely on theoretically derived descriptors and parameters fitted from experimental or computational data, which are often insufficient and biased. Furthermore, outliers and data generated by multiple mechanisms are usually included in the dataset, making the data-driven approach challenging and mathematically complicated. To overcome such issues, we apply the Dempster–Shafer theory to develop an evidential regression-based similarity measurement (eRSM) method, which can rationally transform data into evidence. It then combines such evidence to conclude the similarities between materials, considering their physical properties. To evaluate the eRSM, we used two material datasets, including 3 d transition metal–4 f rare-earth binary and quaternary high-entropy alloys with target properties, Curie temperature, and magnetization. Based on the information obtained on the similarities between the materials, a clustering technique is applied to learn the cluster structures of the materials that facilitate the interpretation of the mechanism. The unsupervised learning experiments demonstrate that the obtained similarities are applicable to detect anomalies and appropriately identify groups of materials whose properties correlate differently with their compositions. Furthermore, significant improvements in the accuracies of the predictions for the Curie temperature and magnetization of the quaternary alloys are obtained by introducing the similarities, with the reduction in mean absolute errors of 36% and 18%, respectively. The results show that the eRSM can adequately measure the similarities and dissimilarities between materials in these datasets with respect to mechanisms of the target properties. [ABSTRACT FROM AUTHOR]

We present efficient numerical methods for the simulation of small magnetization oscillations in three-dimensional micromagnetic systems. Magnetization dynamics is described by the Landau–Lifshitz–Gilbert equation, linearized in the frequency domain around a generic equilibrium configuration, and formulated in a special operator form that allows leveraging large-scale techniques commonly used to evaluate the effective field in time-domain micromagnetic simulations. By using this formulation, we derive numerical algorithms to compute the free magnetization oscillations (i.e., spin wave eigenmodes) as well as magnetization oscillations driven by ac radio-frequency fields for arbitrarily shaped nanomagnets. Moreover, semi-analytical perturbation techniques based on the computation of a reduced set of eigenmodes are provided for fast evaluation of magnetization frequency response and absorption spectra as a function of damping and ac field. We present both finite-difference and finite-element implementations and demonstrate their effectiveness on a test case. These techniques open the possibility to study generic magnonic systems discretized with several hundred thousands (or even millions) of computational cells in a reasonably short time. [ABSTRACT FROM AUTHOR]

State-of-the-art THz spintronic emitters require a constant magnetic field to saturate their magnetization. We demonstrate that depositing the ferromagnetic layers at oblique incidence confines the magnetization to a chosen in-plane easy axis and maintains the saturation in the absence of an external magnetic field. We use this method to build THz emitters structured as spin valves, for which we use an external magnetic field to turn on and off the emission of THz radiation as well as to change its polarization. We are able to reproduce the THz waveforms by modeling the spin current and the THz propagation through the multilayer system. [ABSTRACT FROM AUTHOR]

Magnetically ordered insulators are of key interest for spintronics applications, but most of them have not yet been explored in depth regarding their magnetic properties, in particular with respect to their dynamic response. We study the static and dynamic magnetic properties of epitaxially strained γ -Fe2O3 (maghemite) thin films grown via pulsed-laser deposition on MgO substrates by SQUID magnetometry and cryogenic broadband ferromagnetic resonance experiments. SQUID magnetometry measurements reveal hysteretic magnetization curves for magnetic fields applied both in- and out of the sample plane. From the magnetization dynamics of our thin films, we find a small negative effective magnetization in agreement with a strain induced perpendicular magnetic anisotropy. Moreover, we observe a non-linear evolution of the ferromagnetic resonance-linewidth as a function of the microwave frequency and explain this finding with the so-called slow relaxor model. We investigate the magnetization dynamics and non-linear damping mechanisms present in our samples as a function of frequency and temperature and in particular, observe a sign change in the effective magnetization from the transition of the magnetic anisotropy from a perpendicular easy axis to an easy in-plane anisotropy for reduced temperatures. Its nonlinear damping properties and strain-induced perpendicular anisotropy render γ -Fe2O3 an interesting material platform for spintronics devices. [ABSTRACT FROM AUTHOR]

The recently discovered Fe-As superconducting materials which show high potential ability to carry current due to their low anisotropy have attracted a great number of attentions to understand their superconductivity mechanism and explore their applications. This paper presents a method to synthesis SmFeO0.75F0.20As polycrystalline by hot press in detail. The magnetization at different temperatures and applied fields obtained by a superconducting quantum interference device are also discussed. In addition, the local magnetization process is presented by magneto-optical imaging technique at the conditions of zero-field-cooling and field-cooling. It is found that the collective magnetization process of the newly discovered Fe-As superconductors is very similar to that of high-Tc cuprates. For instance, the Fe-As superconductors and high-Tc cuprates have the same magnetization features due to strong pining and intergrain weak link. The global supercurrent is significantly lower than local grain supercurrent due to the weak line between the grains. [ABSTRACT FROM AUTHOR]

In this paper we report the synthesis and magnetic properties of CoFe2O4 nanoparticles. The nanoparticles with sizes ranging from 6 to 20 nm were prepared in a chitosan matrix. Size selection was achieved by introducing a nonionic surfactant Tween-X, where X={20, 60, 80, and 85}. Aqueous dispersions of Tween-X show micelles with increasing hydrodynamic sizes as X increases. Mössbauer spectroscopy measurements at 300 K show superparamagnetic behavior for the small particles, changing gradually to a blocked magnetic regime as the particle size increases. Magnetization measurements at 300 K show increasing values for the ratio Mr /MHmax and coercive fields (Hc). [ABSTRACT FROM AUTHOR]

This paper reports simulation results on microwave-assisted magnetization reversal in magnetic thin films with perpendicular anisotropy. In comparison with frequency-fixed microwaves, frequency-chirped microwaves have higher efficiency in pumping magnetization precession and, therefore, can lead to more significant reduction in switching fields. Through the use of chirped microwaves, switching with low fields is also possible for large damping films. [ABSTRACT FROM AUTHOR]

In order to resolve two previous conflicting reports on detectable but weak nuclear magnetic resonance (NMR) 33S signals in unenriched EuS, a sample of 33S-enriched EuS was prepared and the NMR and its temperature dependence were measured in the range from 1.3 to 4.2 K. It was verified that the T=0 extrapolated NMR signal has a value of 12.73 MHz (≈39 kG), not 5.4 MHz, as one group had reported. The temperature dependence of the NMR was used to assess the applicability of two proposed spin-wave-region power-law schemes. The schemes attempted to systematize and explain the simple power-law behaviors measured by NMR and other techniques that have been reported (or have been present in measured data, but not reported) for more than five decades. The scheme proposed by Koebler et al. [Physica B 364, 55 (2005)] contends that the low-temperature magnetization of EuS follows a simple T2 behavior all the way up to 0.75Tc. The 33S spin-echo measurements are consistent with a power law, but cast doubt on a T2 dependence. Possible reasons for discrepancies between various EuS NMR measurements are discussed in the paper as well as means of resolving such issues by future experiments. [ABSTRACT FROM AUTHOR]

It is well known that a magnetic field applied onto a Heisenberg antiferromagnet acts as an effective easy-plane anisotropy leading, in the case of two dimensions, to a Berezinskii–Kosterlitz–Thouless transition at a field-dependent temperature. If a nonmagnetic impurity is introduced in the lattice, an island of finite staggered magnetization develops, for which a recently proposed effective model predicts a universal shape that is almost independent of temperature and whose amplitude decays exponentially with the distance from the impurity. This picture was confirmed for the two-dimensional spin-12 case by quantum Monte Carlo simulations, whose outcomes, however, display also a counterintuitive effect: as the temperature approaches the critical value, the field-induced staggered magnetization surprisingly increases its range, which reaches a maximum before definitely dropping to zero in the disordered phase. In this paper an explanation of such a strange behavior is given as the result of vortex excitation. [ABSTRACT FROM AUTHOR]

When an ultrafast laser impinges a magnetic material, it excites charge and then, via spin-orbit-coupling, spin. This holds great promise for the future magnetic storage. However, the coupling of the two dynamics is far from clear, which hampers the experimental effort in femtosecond magnetism. Since not every excitation induces the same spin excitation, a clear understanding of the correlation between charge and spin is crucial. In this paper we investigate in a complete first-principles manner the energy dispersion of the spin-moment change in ferromagnetic Ni and the effect of the distance between the magnetic centers upon the spin localization and local-spin-flip times in metallic chains. Thus we establish the missing link between the spin-momentum change and the density-of-states change, and derive rules-of-thumb for localized spin manipulation. [ABSTRACT FROM AUTHOR]

The bulk polycrystalline samples with nominal compositions Zn0.98-y(Mn/Co)0.02(Al/Sb)yO (y=0, 0.01, and 0.03) have been synthesized via solid state reaction route. The x-ray diffraction results reveal the presence of mainly wurtzite structure of pure ZnO in all the Al/Sb codoped ZnMnO and ZnCoO samples. EDAX results confirm the presence of all elements in the samples in the stoichiometric ratio. While the Zn(Mn/Co)O samples show paramagnetic behavior at room temperature, the Al/Sb codoped ZnMnO samples exhibit room temperature ferromagnetism (RTFM) with saturation magnetization (Ms). The M-H curves of Al/Sb codoped ZnCoO samples show almost linear variation with a small kink at the origin, indicating the presence of weak ferromagnetism in the Al/Sb codoped ZnCoO samples. Possible mechanisms of the observed RTFM in Al/Sb codoped Zn(Mn/Co)O samples are discussed in this paper. [ABSTRACT FROM AUTHOR]

This paper describes a large-scale micromagnetic simulation by using the fast multipole method (FMM) specialized for uniform brick elements. The fast Fourier transform (FFT) is widely used to reduce computational costs of the demagnetizing field calculation. However, the FFT still requires operation counts of O(N log N), where N is the number of elements, which results in the huge computational costs in large-scale problems. To overcome the difficulties, we develop an O(N) approach based on the FMM. In a micromagnetic simulation, an analyzed region is usually subdivided into uniform elements. By making the best use of the periodic structure of uniformly distributed elements, the computational costs of the FMM can be reduced drastically. A large-scale micromagnetic simulation of a single-pole-type head demonstrates the effectiveness of the specialized FMM from the viewpoints of calculation time and memory requirements, compared with the FFT. [ABSTRACT FROM AUTHOR]

To study the connection between macroscopic hysteretic behavior and the microstructural properties, this paper presents and validates a new material dependent three-dimensional mesoscopic magnetic hysteresis model. In the presented mesoscopic description, the different micromagnetic energy terms are reformulated on the space scale of the magnetic domains. The sample is discretized in cubic cells, each with a local stress state, local bcc crystallographic axes, etc. The magnetization is assumed to align with one of the three crystallographic axes, in positive or negative sense, defining six volume fractions within each cell. The micromagnetic Gibbs free energy is described in terms of these volume fractions. Hysteresis loops are computed by minimizing the mesoscopic Gibbs free energy using a modified gradient search for a sequence of external applied fields. To validate the mesohysteresis model, we studied the magnetic memory properties. Numerical experiments reveal that (1) minor hysteresis loops are indeed closed and (2) the closed minor loops are erased from the memory. [ABSTRACT FROM AUTHOR]

Recently reported results on domain wall propagation within the inner core of bistable Fe-based positive magnetostrictive amorphous microwires opened up the way for future spintronic applications of amorphous microwires. Domain wall propagation has also been investigated in Co-based nearly zero magnetostrictive microwires, which become bistable under certain conditions. Wall velocity and mobility values were found to be superior in the latter type of microwires due to their much smaller magnetoelastic anisotropy. In this paper, the key role played by the surface domain structure of microwires in determining the wall mobility is investigated. Wall velocity measurements have been performed on (Co0.94Fe0.06)72.5Si12.5B15 microwires in as-cast glass-coated state and after glass removal with a hydrofluoric acid solution. Surface magnetization has been studied employing magneto-optical Kerr effect. The results show that both as-cast glass-coated microwires and microwires with the glass coating removed, which are bistable, display a helical magnetization in the surface region. The direction of the magnetization in this region affects the mobility of the propagating wall due to the stray fields associated with the preponderant components of the magnetization. [ABSTRACT FROM AUTHOR]

This paper describes the microwave properties of low temperature fired Ni0.6CuxZn(0.4-x)Fe1.96+δO4 gyromagnetic ferrite material synthesized by conventional oxide process with Bi2O3 additives. It is found that 60–63 mol % Ni and 5 mol % Cu contents have the advantage to keep the material with both low-fired characteristic and high saturated magnetization with 3 wt % Bi2O3 additives. Considering the conditions of milling, calcination, and sintering process, the low temperature fired NiCuZn gyromagnetic material was prepared with excellent microwave performances. The saturated magnetization Ms of the sample is 337 kA/m, the ferromagnetic resonance linewidth ΔH and dielectric loss tgδ[variant_greek_epsilon] less than 16 kA/m and 5.7×10-4, respectively, which has the potential applications for low temperature cofired ceramics technology to develop microwave chip circulator/isolator and passive integrated substrate. [ABSTRACT FROM AUTHOR]

In their seminal 1935 paper on magnetics, Landau and Lifshitz (LL) proposed a form for magnetization damping. In 1955 Gilbert proposed another form, introducing a dimensionless parameter α. We derive LL damping using the theory of irreversible thermodynamics, summarize an unbiased Langevin theory of fluctuations that yields LL damping, and argue that inhomogeneous broadening might explain the nonresonance data that led Gilbert to formulate his theory. LL versus Gilbert damping takes on special relevance in the context of bulk spin transfer torque and bulk spin pumping, where the form of damping affects the values of the “adiabatic” and “nonadiabatic” terms. We argue that the adiabatic and nonadiabatic terms are dissipative and reactive, respectively. [ABSTRACT FROM AUTHOR]

The color in oil paints is obtained sometimes from magnetic minerals. This fact implies that oil paintings could present an intrinsic magnetization. Magnetic imaging of an oil painting consists in the measurement of magnetic flux related to the magnetization of the painting. In this report results of magnetic measurements show that oil paints from different manufacturers (Maimeri, Pebeo, and Grumbacher) are magnetic. The magnetic imagings of four similar oil paintings done with the same visual color, obtained using different mixtures of oil paints for each painting, were different. This shows that the magnetic imaging can be used as a fingerprint for the oil paintings. Magnetic imaging was obtained for oil paintings done by Oswald, Bianco, and Timoteo, all of them are Brazilian painters. The imaging obtained in measurements at different times was always the same, showing that the magnetic images are stable. This leads to the conclusion that magnetic imaging would be a common authentication technique of paintings. [ABSTRACT FROM AUTHOR]

This paper focuses on the magnetization dynamics induced by the balance between the physical positive damping and the negative induced by spin-transfer torque in point-contact devices. We consider an applied field perpendicular to the device plane which both saturates the magnetization of the free layer and tilts the one of the pinned layer about 30° out-of-the-film plane. The influence of the nonuniform current-induced magnetic (Oersted or Ampere) field on the magnetization dynamics of such oscillators has been taken into account within a micromagnetic framework. Results of micromagnetic calculations show that the Oersted field yields spatial asymmetries in the magnetization configuration, which do not introduce any modifications in the frequency domain. Finally, Slonczewski’s analytical formulation [J. Magn. Magn. Mater. 159, L1 (1996)] about the spatial geometry of the current-excited spin-wave modes has been validated numerically. [ABSTRACT FROM AUTHOR]

This paper presents a theoretical study about the effect of nonidealities in the shape of elliptical cross sectional area of magnetic tunnel junctions on the magnetization dynamics driven by spin-polarized currents (no applied field). The set of nonideal shapes has been computed from scanning electron microscopy images directly. The polarization function deduced by Slonczewski in 2005 [Phys. Rev. B 71, 024411 (2005)] has been used for the simulations, considering the polarization factor independent of the bias. Depending on the shape, results of micromagnetic simulations show that the main steps of the magnetization dynamics do not change qualitatively, but in contrast, (a) other modes (defect modes) are excited, (b) a shift in the excited main mode is observed, and (c) the spatial distribution of the main mode changes. [ABSTRACT FROM AUTHOR]

In this paper, two methods for the synthesis of magnetic nanotubes inside the pores of anodic alumina membranes by atomic layer deposition (ALD) are compared. The precursors were nickelocene or cobaltocene, and H2O or O3. The first method consists of a three-step ALD cycle: First, the sample is exposed to the metal-organic precursor, subsequently to water, and finally, to hydrogen. In the second method, metal oxide is deposited by a conventional two-step ALD cycle. After the ALD process, the sample is reduced under hydrogen atmosphere. The magnetic nanotubes obtained by the second method have a smaller grain size and improved magnetic properties. The magnetic nanotubes with diameters ranging from 35 to 60 nm exhibit a preferential magnetization direction along the nanowire axis. The Ni or Co nanotubes with larger diameters (around 160 nm) show a nearly isotropic magnetic behavior, with the magnetic moments arranged in a vortex state at zero field. [ABSTRACT FROM AUTHOR]

Up to this date, the conventional electromagnetic force calculation methods such as Maxwell stress, virtual work, Kelvin’s formula, equivalent magnetic charge, and equivalent magnetizing current produce results where the surface component takes up a major portion of the total force, with the portion of the body force being very small or even none. As the formulation of the above mentioned methods starts from the concept of body or volume force, there has been controversy over the true concept of electromagnetic force identity. In this paper, it is shown that electromagnetic body force, which is also called volume force, can be calculated using virtual air-gap scheme that is derived from the generalized equivalent source methods. For the body force calculation, the application of virtual air gap is extended to calculate the force of each finite element as if an element is an independent body surrounded by virtual air gap. The force calculation methods adopted in this paper include Maxwell stress, magnetic charge, and magnetizing current. The examination of the calculated force distribution shows that the force can be expressed only as body force distribution. The total force calculated by the volume integration of the body force on the magnetized body agrees well with the total force calculated by conventional approaches. [ABSTRACT FROM AUTHOR]

In this paper, we report on a detailed study of reversal in the antiferromagnetic layer in IrMn-based exchange-biased systems. By a process of careful field cycling and heating with the antiferromagnet aligned in the opposite direction to the original set direction, we are able to study thermal activation over the energy barriers in the antiferromagnetic material. We find that the peak in the coercivity is observed, but in no way correlates to the blocking temperature. We conclude that the origin of the coercivity enhancement in exchange-biased systems lies in effects at the interface. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In this paper, we deal with antiferromagnetic (AFM) films using the many-body Green’s function theory under random phase approximation (RPA). This is the first time to be able to calculate all three components of the magnetization of AFM systems simultaneously under RPA. The magnetization of AFM films is not so easily affected by external fields as FM films and the magnetic behavior is rather different from FM films. When an external field Bz is applied along the z direction, the parallel susceptibility χ∥ is zero at 0 K, and then increases with temperature until Néel point TN. If a field along the x-direction Bx is applied, the perpendicular susceptibility can be approximately expressed as χ⊥=1/2γ|J|, which is a temperature-independent constant, where γ is the nearest neighbor and J is the exchange interaction. In this case the z-component magnetization is nonzero above TN. This is because the x-component magnetizations of both sublattices are not zero and the AFM exchange should play a role, which results in the antiparallel z-component magnetizations of the two sublattices. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]