Electrical switching of the vortex core in a magnetic disk

A magnetic vortex is a curling magnetic structure realized in a ferromagnetic disk, which is a promising candidate for a memory cell for future non-volatile data-storage devices. Thus, an understanding of the stability and dynamical behaviour of the magnetic vortex is a major requirement for developing magnetic data-storage technology. Since the publication of experimental proof for the existence of a nanometre-scale core with out-of-plane magnetization in a magnetic vortex, the dynamics of vortices have been investigated intensively. However, a way to electrically control the core magnetization, which is a key for constructing a vortex-core memory, has been lacking. Here, we demonstrate the electrical switching of the core magnetization by using the current-driven resonant dynamics of the vortex; the core switching is triggered by a strong dynamic field that is produced locally by a rotational core motion at a high speed of several hundred metres per second. Efficient switching of the vortex core without magnetic-field application is achieved owing to resonance. This opens up the potentiality of a simple magnetic disk as a building block for spintronic devices such as a memory cell where the bit data is stored as the direction of the nanometre-scale core magnetization.     

Statistical data analysis of magnetic recording noise mechanisms

Statistical data analysis using empirical eigenfunctions, known as the Karhunen-Loeve (K-L) expansion, is applied to characterize noise mechanisms in magnetic recording. Given any original data set and hence its correlation (covariance) matrix, an empirical orthogonal set of eigenfunctions can be obtained. The original data set can be expressed as an orthonormal expansion of these eigenfunctions. This feature of the K-L expansion can be used to study dominant noise profiles extracted from a large number of magnetization transition data. Two simple models of magnetization transitions are first utilized to investigate the validity of this expansion. Noises induced by transition center shifting (jitter), transition width fluctuation, amplitude modulation, and combined effects are respectively identified by the first several most important eigenfunctions in the expansion. Eigenfunction expansions of transition data obtained from experiments and numerical simulations are also obtained     

Correlation Between AC Core Loss and Surface Magnetic Barkhausen Noise in Electric Motor Steel

Core loss is a significant source of energy loss in electric motor steel laminates. Therefore, there is interest in monitoring the quality and consistency of laminates at various stages of manufacturing. The purpose of this study was to investigate the feasibility of using surface magnetic Barkhausen noise for the evaluation of AC core loss, and further, to examine potential origins of magnetic loss in non-oriented electrical steel. Core loss values were measured by a single sheet tester and Barkhausen noise measurements were performed using pole flux control on eight laminates with various grain size, texture and composition. Magnetocrystalline energy was calculated from X-ray diffraction data to quantify texture. Results demonstrated higher surface Barkhausen emissions for samples with lower core loss. Barkhausen noise analyses were used to examine the interplay among core loss, grain size, magnetocrystalline energy and B–H characteristics. The inverse correlation between core loss and Barkhausen noise emissions was qualitatively explained in terms of the orthogonal vector contribution of microscopic eddy currents to losses associated with bulk currents arising in the sample during magnetization.     

Magnetically Induced Potential Noise (MIPN)—A New Method for the Characterization of Magnetic Materials and for New Sensor Applications

Abstract

This paper discusses a new methodology for characterizing the magnetic properties of ferromagnetic materials. The method uses an alternating electric current to periodically magnetize ferromagnetic materials. The periodic magnetization generates a high-frequency electric potential noise between two electrodes within the excitation circuit. The magnetically induced electric potential noise (MIPN) is related to the discontinuous processes that occur during magnetization similar to magnetic Barkhausen noise. This paper discusses the results of several experiments that measured both electric potential noise and Barkhausen noise signal. A comparison of the results showed that the MIPN correlates directly to magnetic Barkhausen noise. The MIPN signal is small when compared to Barkhausen noise, but it is still easy to measure under laboratory conditions. Therefore, MIPN could be an efficient technique for materials characterization and sensor technology, for example, as fiber stress sensors in a composite aircraft component.     

Magnetically Induced Potential Noise (MIPN)—A New Method for the Characterization of Magnetic Materials and for New Sensor Applications

This paper discusses a new methodology for characterizing the magnetic properties of ferromagnetic materials. The method uses an alternating electric current to periodically magnetize ferromagnetic materials. The periodic magnetization generates a high-frequency electric potential noise between two electrodes within the excitation circuit. The magnetically induced electric potential noise (MIPN) is related to the discontinuous processes that occur during magnetization similar to magnetic Barkhausen noise. This paper discusses the results of several experiments that measured both electric potential noise and Barkhausen noise signal. A comparison of the results showed that the MIPN correlates directly to magnetic Barkhausen noise. The MIPN signal is small when compared to Barkhausen noise, but it is still easy to measure under laboratory conditions. Therefore, MIPN could be an efficient technique for materials characterization and sensor technology, for example, as fiber stress sensors in a composite aircraft component.     

Methodology for investigating the magnetization Process of the storage Layer in double-Layered perpendicular magnetic recording media using the anomalous Hall effect

The Hall effect is a useful phenomenon for evaluating the magnetization processes of the storage and back layers in double-layered perpendicular magnetic recording media. Although the Hall voltage in double-layered films has two components (an anomalous Hall term arising from the perpendicular component of magnetization and a planar Hall term originating from the in-plane component of magnetization), it is possible to separate the two contributions by symmetry arguments. However, in the case where the saturation field of the recording layer (RL) is comparable to that of the soft underlayer (SUL), or when the SUL dominates the signal because of its inherently high magnetic moment, it is difficult to separate the anomalous Hall effect (AHE) contributions from the RL and SUL individually. Here we propose a methodology that overcomes this limitation and allows the extraction of the magnetization process of the RL. We assume that an average perpendicular magnetization contributes to the anomalous Hall voltage in the double-layered perpendicular media. We compare the magnetization process of the RL obtained by using this approach to that measured with a magnetooptical Kerr effect (MOKE) system. The proposed technique may be useful in those situations in which alternative tools such as the MOKE system are not suitable for measuring the magnetization process.     

Flux-Closure Magnetic States in Triangular Cobalt Ring Elements

Ferromagnetic ring elements on the micrometer and submicrometer scale exhibit flux-closure magnetic vortex states in an intermediate step of their magnetization reversal. These clockwise or counterclockwise flux-closure states are of interest for applications that encode binary information in magnetic elements. Here, we study the magnetization reversal process of triangular cobalt rings made by e-beam lithography and lift-off. We demonstrate that full control over the direction of flux-closure magnetic states can be achieved solely by homogeneous external magnetic fields applied in particular directions. We have extracted statistical experimental data pertaining to the range of critical field values that trigger magnetization reversal from magnetic force microscopy images, and we explain the results on the basis of micromagnetic simulations     

A new surface transducer for generating and detecting magnetic field transients in ferromagnetics

A new surface transducer is described for generating and detecting magnetic field transients or magnetization discontinuities in ferromagnetic materials [8]. The sensing is based on searching for transients of the magnetic potentials which would be likely to occur on the surface of the specimen. A coil core of high-frequency ferrite is used for this. The sensor theory presented shows the coaxial geometry of the coil core to be that which is more practicable for limiting detection to a compact volume of the specimen to be analyzed. The fundamental noise and disturbance analyses performed show adequate margins for wideband noise and external stray field disturbances. The transducer electronics for generating the varying external magnetic field in the specimen and for detecting the occurring field transients are described with a view to the optimization of the electrical circuits, and the resulting specifications are discussed. The surface transducer constructed is widely applicable for studying the magnetization characteristics of different ferromagnetics nondestructively in conjunction with stochastic-ergodic analyzers such as a pulse-height analyzer or a digital correlator through a punch-tape recorder or in on-line connection with a computer [7].     

The application of multistable magnetic cores for dialing purposes in telephony

Multistable magnetic cores have the well-known property that a certain amount of flux, stored in the core, remains unchanged for a long time. This amount of flux can be broken down by feeding a number of voltage pulses, with a constant volt-second integral and the right polarity, to a core winding. Each of these readout pulses will lower the flux level in the core until there is no flux left, and from that moment a readout pulse only causes a small reversible change in flux, setting up a very short induction EMF in the core windings. A simple integrating network can be used to judge the output voltage of a winding, and it gives no output if the former results from a reversible flux change. If the pulse generator has a repetition frequence of ten cycles per second, the output pulses of the integrating network, after being shaped by a monostable trigger, will be suitable for dialing purposes in conventional telephone systems. A predetermined amount of flux, corresponding to one of the numbers one to ten, can easily be obtained by discharging a loaded condenser in series with a resistance through a core winding.     

New Magnetic Field Sensor Based on Combined Flux-Gate/Hall-Effect Arrangement

A novel planar magnetic field sensor is presented that is based on a combined flux-gate/Hall-effect arrangement capable of measuring the three components of a three-dimensional quasi-static magnetic field. The proposed device involves a thin, isotropic, circular magnetic core, the magnetization of which is driven to saturation by means of a rotating excitation-field, produced by four printed planar coils. That way, the core magnetization rotates, without Barkhausen jumps inducing a flux-density change that is sensed by a Hall device positioned at the edge of the core. The presented sensor consists of a discrete Hall device, electronic modulation-demodulation circuitry and a circular amorphous core packaged on a printed circuit board (PCB), constructed as a proof of concept for the proposed magnetic field measuring method.     

Magnetic Barkhausen emission study in heat-treated Fe-Nb-Cu-Si-B alloy

Magnetic hysteresis and magnetic Barkhausen emission (MBE) parameters have been studied for as-received and annealed Fe/sub 72/Nb/sub 4.5/Cu/sub 1/Si/sub 13.5/B/sub 9/ alloys. The coercivity rapidly decreased at the initial stage of annealing, in contrast to the slow change of root-mean-square voltage of Barkhausen emissions. The amplitude of the Barkhausen emission signal reduced almost to the background noise level at an intermediate annealing temperature, at which the material exhibited superior soft magnetic properties. Pulse height distribution of the MBE signal showed the existence of a large number of small amplitude pulses at the intermediate range of annealing, an indication that the magnetization process of the system is dominated by the rotation of the magnetization vector within a small volume of nanocrystalline particles. We explain the results by a random anisotropy model, assuming the exchange coupling between the Fe/sub 80/Si/sub 20/ nanograins of higher magnetic moment takes place through the magnetically weaker amorphous matrix.     

Induction of coherent magnetization switching in a few atomic layers of FeCo using voltage pulses

The magnetization direction of a metallic magnet has generally been controlled by a magnetic field or by spin-current injection into nanosized magnetic cells. Both these methods use an electric current to control the magnetization direction; therefore, they are energy consuming. Magnetization control using an electric field is considered desirable because of its expected ultra-low power consumption and coherent behaviour. Previous experimental approaches towards achieving voltage control of magnetization switching have used single ferromagnetic layers with and without piezoelectric materials, ferromagnetic semiconductors, multiferroic materials, and their hybrid systems. However, the coherent control of magnetization using voltage signals has not thus far been realized. Also, bistable magnetization switching (which is essential in information storage) possesses intrinsic difficulties because an electric field does not break time-reversal symmetry. Here, we demonstrate a coherent precessional magnetization switching using electric field pulses in nanoscale magnetic cells with a few atomic FeCo (001) epitaxial layers adjacent to a MgO barrier. Furthermore, we demonstrate the realization of bistable toggle switching using the coherent precessions. The estimated power consumption for single switching in the ideal equivalent switching circuit can be of the order of 10(4)k(B)T, suggesting a reduction factor of 1/500 when compared with that of the spin-current-injection switching process.     

Fabrication and characterization of giant magnetoresistive elementswith an integrated test coil

Magnetoresistive elements (MREs) containing exchange-biased spin valve multilayers as the magnetoresistive material have been fabricated. Their electrical response has been measured using an integrated test coil. Both parallel and crossed arrangements of the easy axes of the free and biased layers have been studied. Output voltage levels of these elements in response to an ac magnetic field are typically a factor of 7-10 higher than those obtained in similar elements based on a conventional, 30 nm thick anisotropic magnetoresistive (AMR) Ni₈₀ Fe₂₀ film linearized by the “barber-pole” method. The parallel arrangement is found to result in a switching behavior which is characteristic of domain wall movement and contains hysteresis, Barkhausen noise, and strong harmonic distortion. The arrangement with crossed anisotropies is found to display a behavior characteristic of switching by magnetization rotation as evidenced by a strong reduction of hysteresis, Barkhausen noise, and harmonic distortion. Demagnetization effects are calculated in order to quantitatively explain the shape of the response curve and the difference in output voltage when compared to AMR-based MREs     

A computer-aided design procedure for flyback step-up DC-to-DC converters

A flyback step-up dc-to-dc power converter is modeled utilizing a linear magnetic core, transistor switch, diode, filter capacitance, and load resistance. Assuming constant voltage drops across the semiconductor elements when conducting, the circuit is analyzed to obtain an equation for the required number of turns, subject to the constraints of specified output voltage, operating frequency, maximum winding factor, maximum and minimum input voltage, output power, and flux density. Using an interpretive language, a program has been written to run on a minicomputer which searches a data base of magnetic core characteristics obtained from commercial core catalogs and prints a list of windable cores. In an evaluation section of the program, a core from the windable core list is selected by the designer and the losses in the various elements, along with maximum and minimum transistor current are computed. Another program is used to display on a computer graphics device the loci of maximum and minimum flux density in a selected core as functions of input voltage and output power in a perspective plot. Converter circuits derived from this computer-aided design procedure when tested in the laboratory have yielded data in close agreement with that predicted by the program.     

Model for demagnetization-induced noise in thin-film magneticrecording media

A linear, statistical model is described which predicts the power spectrum of measured noise in bulk-demagnetized (i.e. AC-erased) thin-film magnetic recording media. It is shown that the noise is the result of magnetic flux which is ascribed to erasure-induced transitions along the track length in the medium. The noise power spectrum for a rigid disk medium is shown to correspond to the power spectrum of Poisson-distributed induced transitions along the track length, while noise along the track width is sufficiently described in terms of a uniform, average magnetization with small variance. Experimental data from two thin-film disks are used with the model to estimate the Poisson parameter for each disk. It is demonstrated that AC-erased noise from particulate media can be considered as a limiting case of the Poisson model     

Effect of bias field and stress on Barkhausen noise in pipeline steels

Surface Barkhausen noise (SBN) and encircle Barkhausen noise (EBN) measurements have been made on pipeline steel under different positive and negative DC bias field conditions. The effects of bias field on both SBN and EBN are found to be similar. With increasing positive and negative bias the Barkhausen noise (BN) is found to decrease, and at higher bias fields the BN disappears. The results confirm that magnetization in the low-field region (below 0.5 T) takes place by 180° wall motion which gives rise to magnetic BN. Tensile and compressive stresses have been applied in a section of the pipe and SBN measurements made. The SBN voltage is found to increase with tension and to decrease with compression.     

非晶丝微磁化线圈磁电阻抗效应研究

本文研究了铁基及钴基非晶态合金丝在由微磁经线圈所产生的轴向交变磁场的作用下所呈现的磁电阻抗效应，经出了一些测试结果，结果表明，微磁化线圈两端的电压信号峰－峰值随轴向外磁场Ｈｅ的增加而单调减少，钴基非晶丝可呈现巨磁电阻抗效应，利用该效应可制成新型磁敏元件及器件。     

Fe78Si9B13非晶合金磁芯封装及其软磁性能

研究了Fe78Si9B13非晶合金磁芯进行环氧封装及封装后对非晶合金磁芯软磁性能的影响。结果表明对磁芯进行环氧封装,有效改善磁芯的机械强度同时,能改善带材表面的平整度,在带材表面形成一层绝缘层,显著降低了非晶合金磁芯高频下的损耗值,封装后的非晶合金磁芯在Bm=1T,f=1kHz下,损耗值比封装前下降了14%。综合考虑机械强度大小、磁化难易、损耗高低等因素,封装胶浓度为2%时封装效果最佳。     

An integrated superconductive magnetic nanosensor for high-sensitivity nanoscale applications

An integrated magnetic nanosensor based on a niobium dc SQUID (superconducting quantum interference device) for nanoscale applications is presented. The sensor, having a washer shape with a hole of 200?nm and two Josephson-Dayem nanobridges of 80?nm × 100?nm, consists of a Nb(30?nm)/Al(30?nm) bilayer patterned by electron beam lithography (EBL) and shaped by lift-off and reactive ion etch (RIE) processes. The presence of the niobium coils, integrated on-chip and tightly coupled to the SQUID, allows us to easily excite the sensor in order to get the voltage-flux characteristics and to flux bias the SQUID at its optimal point. The measurements were performed at liquid helium temperature. A voltage swing of 75?μV and a maximum voltage-flux transfer coefficient (responsivity) as high as 1?mV/Φ(0) were directly measured from the voltage-flux characteristic. The noise measurements were performed in open loop mode, biasing the SQUID with a dc magnetic flux at its maximum responsivity point and using direct-coupled low-noise readout electronics. A white magnetic flux noise spectral density as low as 2.5?μΦ(0)?Hz(-1/2) was achieved, corresponding to a magnetization or spin sensitivity in units of the Bohr magneton of 100?spin?Hz(-1/2). Possible applications of this nanosensor can be envisaged in magnetic detection of nanoparticles and small clusters of atoms and molecules, in the measurement of nanoobject magnetization, and in quantum computing.