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1.
In magnetic bubble memory packages having a bias field HBsupplied by a Ba-ferrite permanent magnet structure, the magnitude of HBmay be appreciably altered after setting by transient exposure to externally applied magnetic fields Hextas much as 10 times smaller than the field used in setting HB. We examine this effect for a particular magnet design having a permalloy yoke, a gap of 0.270 inches, and a saturation fieldH_{sat} simeq 240Oe. We find that the magnitude of the effect depends upon the ratioH_{B}/H_{sat}and upon the procedure used in setting HB. After setting toH_{B} = 200Oe from saturation with a demagnetizing fieldH_{ext} = -1400Oe, a remagnetizing fieldH_{ext} simeq 1800Oe is required to increase HBby 1%. On the other hand, after setting toH_{B} = 100Oe withH_{ext} = -2300Oe, a remagnetizing fieldH_{ext} simeq 400Oe is sufficient to increase HBby 1%. Setting by demagnetizing from saturation yields superior stability to setting by magnetizing from the demagnetized state, and stability of the set magnet may be further improved by demagnetizing with a ringing (alternating) field. This behavior is explained with a simple model and its importance for magnet design is discussed.  相似文献   

2.
The operation of a bubble-domain straight-line propagation circuit has been simulated successfully. This simulation has been achieved by our approximating the motion of an s = 0 frozen-azimuth bubble placed under a drive fieldH_{Z}(X, Y, T)= -H_{p} cdot cos [2pi(X/R_{X} - n(T)/4)] cdot exp [-(Y/R_{Y})^{2}]. The simulation has been generated from a previously developed numerical scheme to simulate the motion of a bubble, whose domain shape and magnetization structure along its domain wall were variable. The drive field has been modeled after a dual conductor-sheet, current-access propagation structure, which has a bit period RXand a transverse width on the order of2R_{Y}. The entire field contour has been advanced stepwise in the positiveXdirection by an increase of the integern(T), which represents the drive-phase number. The bubble motion has been observed during the first six drive phases to produce operating margin diagrams for drive frequencies of 250 KHz, 796 KHz and 1 MHz. The method of calculation and the results of the simulation are given.  相似文献   

3.
Multidomain ferromagnetic resonance (FMR) for Permalloy magnetic fills (thickness 2700 Å) 83 percent Ni with rotatable anisotropy was experimentally observed with an external magnetic field applied normal to the sample surface. The lower frequency branch of multidomain FMR was excited when the RF magnetic fieldhwas oriented along the film plane; forhoriented parallel to the fieldH_{perp}the higher frequency branch was excited. The dependence of the resonant fieldH_{perp}on the frequency of fieldhfor multidomain and single-domain FMR was determined. Increasing the RF fieldhoriented alongH_{perp}gave rise to oscillations of magnetization with the frequency(1/2)f, wherefis the pumping frequency. The dependence of the amplitude of these oscillations on the strength of the RF fieldhand on the magnetizing fieldH_{perp}was investigated.  相似文献   

4.
The described method for the anisotropy field measurement uses two fields HLand HT. The deviation of magnetization from the easy direction, and hence also sense signals, are proportional to these fields. The ratio of two integrated sense signals atH_{L} = 0andH_{L} neq 0reaches a certain value (∼ 2.5) with fieldH_{T} = H_{k}. In this way, Hkmay be measured by a device designed for the coercive force measurement.  相似文献   

5.
The dependence ot the in-plane drive field at which bubble domains spontaneously nucleate in field-accessed bubble devices has been investigated as a function ofH_{k} - 4piM_{s}and of spacer thickness between the bubble film and permalloy propagation elements. The experiments were carried out on amorphous GdCoMo bubble films with T-bar and Y-bar structures. For a given structure and spacer thickness the nucleation field increases linearly withH_{k} - 4piM. Larger spacer thicknesses also lead to increased nucleation fields. A model based on the Stoner-Wohlfarth astroid is compared to these data and found to be useful in explaining the qualitative trends, but to be in poor quantitative agreement. It is concluded that since the drive field required in a device is proportional to4piM_{s}, Q - 1 = (H_{k} - 4piM_{s})/4piM_{s}must be greater than some minimum value for a given device structure and spacer thickness to permit reliable device operation.  相似文献   

6.
A simple model is presented which allows accurate prediction of bias margins of gap-tolerant half-disk propagation tracks for bubble domains. After this is verified by comparison with experimental margin data, an "isomargin" plot is derived to show how the margin varies as a function ofWandG, whereWis the minimum linewidth andGis the inter-bar gap. The bias margin is shown to decrease along a fairly straight line which goes to zero whenW + Gequals the runout diameter, i.e., whenW+G approx 1.5 W_{s}, where Wsis the bubble stripwidth or average bubble diameter. This agrees with experiment, and means that the minimum resolvable feature for half-disk type patterns must be less than0.75W_{s}, and probably will not be much larger than0.5W_{s}to0.6W_{s}. It is concluded that, if made with perfect Permalloy, T-bars and half-disks should propagate isolated bubbles equally well. The advantages of half-disks over T-bars are 1) the fatal bar-crossing problem of T-bars with multiple bubbles is avoided, 2) the minimum propagation field is lower than for T-bars, and 3) half-disks seem more tolerant of "bad" (e.g., high-coercivity) Permalloy. Also tabulated are the effects on margins of variations in the device parameters of a representative design, as might be encountered in a fabrication process with finite tolerances. A brief discussion of stop-start margins is given in conclusion.  相似文献   

7.
It is shown that the one-dimensional studies of the wall surrounding a bubble domain do not violate some necessary self-consistency requirements. Moreover, it is shown that the ratio of the magnetostatic self energy (which is neglected in these studies) to the total one-dimensional wall energy isT/Q, whereTis of the order of 1 for typical film thickness of a typical bubble material. This justifies the use of the one-dimensional wall for these materials, as long as the quality factorQ = K/(2piMmin{s}max{2})is large.  相似文献   

8.
The anhysteretic remanencebar{M}_{ar}(H_{o},T)of solidified suspensions of magnetic particles with predominant shape anisotropy is calculated from first principles for small dc fields Hoand arbitrary temperatureT < T_{B}(blocking temperature), describing the particle interactions by a mean field and assuming constant decrement of the ac field,2H_{d}per cycle. ForH_{d}< 2H_{o}, the anhysteretic distribution of particle magnetizations is found to be subject to the condition that the net internal dc fieldbar{H}_{i}is a minimum, and, for small Ho, to the condition,bar{H}_{i} = 0. The theory yieldsbar{M}_{ar}(H_{o},T)as a unique function of independently measurable static magnetic material properties, i.e., it contains no adjustable parameters and is hence quantitatively related to experimental data. Further, according to theory, ifbar{M}_{ar}(H_{o},T,T_{m})denotesbar{M}_{ar}as acquired in Hoat T and measured atT_{m}, bar{M}_{ar}(H_{o},T,T_{m} = T)is independent ofTforH_{d} ll 2H_{o}, andbar{M}_{ar}(H_{o},T,T_{m} neq T) = [M_{s}(T_{m})/M_{s}(T)] cdot bar{M}_{ar}(H_{o},T,T_{m} = T). The thermoremanent magnetization acquired in Hoand measured at a temperatureT_{m} ll T_{B},bar{M}_{thr}(H_{o},T_{m}), is related tobar{M}_{ar}(H_{o},T = T_{m}, T_{m})bybar{M}_{thr}(H_{o},T_{m}) = [M_{s}(T_{m})/M_{s}(T_{B})]bar{M}_{ar}(H_{o},T=T_{m},T_{m}), where TBis the blocking temperature below whichbar{M}_{thr}becomes thermally stable. Up to a constant factor of about 2, the theoretical results agree quantitatively with the experimental data on all materials that correspond to the premises of the theory, i.e., solidified suspensions, tapes in particular, of particles having predominant shape anisotropy.  相似文献   

9.
A new principle of operation makes feasible small, cheap potential-independent current comparators whose performance reaches or exceeds the best properties of bulky magnetic amplifiers of the second-harmonic type. Connection of a ferrite-core coil in parallel with a suitable negative resistance generates relaxation oscillationsg(t). Inherently, at large oscillations the coil (i,phi)- characteristic is perfectly symmetric about the origin:phi(-i) = -phi(i). Provided that the negative-resistance (i,u)- characteristic has the same symmetry:i(-u) = -i(u), the oscillationsg(t)are perfectly symmetrical in the sense thatg(t+T/2) = -g(t). Heregrepresents either the coil flux φ, the currentior the voltageu. The time istandTthe oscillation period. External magnetomotive force shifts the coil (i,phi)-characteristics, invalidating (1) and therefore (3). Consequently, the deviation from 50% duty-ratio of the oscillatingq(t)is a sensitive and extremely stable measure of this MMF. Neither core temperature, pressure nor magnetic creep cause any zero drift. Orders of magnitude reached experimentally are: Short-time zero instability and noise:leq 10^{-5}ampere-turn, time resolution:leq 10^{-4}s, zero drift from -70 to +100°C:< 10^{-4}ampere-turn.  相似文献   

10.
We investigated the $(hbox{Bi}_{rm x}hbox{Dy}_{rm y}hbox{Yb}_{3-{rm x}-{rm y}})hbox{Fe}_{5}hbox{O}_{12}$ ternary combinatorial composition spread with the goal of finding new compositions with a large magneto-optical effect for possible use as magneto-optical storage materials. High-throughput magneto-optical characterization of the spread showed that the $hbox{Dy}_{0.6}hbox{Yb}_{0.5}hbox{Bi}_{1.9}hbox{Fe}_{5}hbox{O}_{12}$ composition has the largest Kerr effect in this ternary system. After annealing at 690 $^{circ}hbox{C}$ for 1 h, a scaled-up thin-film sample of this composition has a remanent magnetization as high as 90% of its saturation magnetization, indicating a good storage application potential.   相似文献   

11.
We propose a theoretical design for a magnetic memory cell, based on thin-film ferromagnetic nanorings, that can efficiently store, record, and read out information. An information bit is represented by the polarity of a stable 360$^{circ}$ domain wall introduced into the ring. Switching between the two magnetization states is done by a current applied to a wire passing through the ring, whereby the 360$^{circ}$ domain wall splits into two charged 180 $^{circ}$ walls, which then move to the opposite extreme of the ring to recombine into a 360 $^{circ}$ wall of the opposite polarity.   相似文献   

12.
The magnetic coupling between the magnetization in two nonmagnetostrictive Ni-Fe layers separated by a SiO layer has been investigated by means of a transverse susceptibility measurement. The main results are that 1) the coupling energy Ec per Unit area of the multilayered film has a form ofE_{c}= -A cos (phi_{1}-phi_{2}), wherephi_{1}-phi_{2}is the angle between the magnetization vectors in the two Ni-Fe layers, and 2) the dependence of the coupling constant on the thickness b of the intermediate SiO layer can be interpreted quantitatively by the combination of the coupling energy due to Néel's topography model and that due to the magnetostatic interaction between the magnetic free poles appearing at the edges of the two Ni-Fe layers. The former coupling energy is given byE_{c1} = -frac{p}{2sqrt{2}}omega^{2}M^{2} exp(-sqrt{2}pb) cos (phi_{1}-phi_{2})wherep=2pi/LandLandware the wavelength and the amplitude of the undulation of the interface between Ni-Fe and SiO layers, respectively. The latter is given byE_{c2} = frac{2M^{2}D^{2}}{R} ln (frac{R}{D+b}) cos (phi_{1}-phi_{2})whereDis the thickness of each Ni-Fe layer, andRis the radius of the film.  相似文献   

13.
《IEEE sensors journal》2008,8(9):1539-1545
Sensitive and selective gas measurements are crucial for a large variety of applications. This paper describes the manufacturing and characterization of a photoacoustic gas sensor system. The system is based on a pressure sensor element with a sensitivity of 10 $mu$ V/V/Pa. To demonstrate and evaluate the concept, 12 prototypes for measuring CO$_{2}$ have been manufactured and characterized. Detection limits ranging from 92 ppm to below 6 ppm CO$_{2}$ were obtained with a path length of 10 cm, depending on the measurement time and photoacoustic cell design. Measurements showed no cross-sensitivity towards CO, CH$_{4}$, or humidity in any of the sensors. The temperature drift of the uncompensated raw signal of two sensor designs was below 117 ppm CO$_{2}$ in the range from 25 $^{circ}$ C to 50 $^{circ}$C.   相似文献   

14.
Superconducting Nb3Sn Cavities have potential advantages over rf cavities with Nb surfaces To test possible applications and to improve the understanding of Nb3Sn coatings on Nb, rf cavities have been measured between 1.5 and 8K and between 0.1 and 7GHz. The temperature dependence of the surface resistance R(T) indicates weak superconducting spots with transition temperaturesTmin{c}max{ast} < 1K andTmin{c}max{ast} simeq 2.5K. The normal conducting spotsTmin{c}max{ast} lsim 1K cause the large rf residual lossesR'_{res} propto f^{2}observed up to date. The spots withTmin_{c}max_{ast} simeq 2.5K cause temperature dependences ofR'(T)between 2 and 6K, where RBCS(Nb3Sn) is still negligible. In line withR_{res} propto f^{2}, the lowest rf lossesR_{res} < 2.10^{-9}Omegaand the highest field strengthB_{crit} = 83 m^{T}(wedgeE_{peak} = 29have been observed at the lowest frequency 0.1GHz measured. Surface resistance and penetration depth measurements have shown that grain boundaries or hydrogen clusters do not cause the weak spots observed withTmin{c}max{ast} < 2.5K. The origin and the chemistry of the weak spots withTmin{c}max{ast} lsim 1K, which cause the largeR_{res} propto f^{2}and the lowB_{crit} (T) simeq const, are still not clear. They seem related to the Nb3Sn surface. The weak spots withTmin{c}max{ast} simeq 2.5K consist most likely of Nb6Sn5, which in cooling below 950°C precipitates due to the excess Sn present in Nb3Sn coatings grown in Sn vapor.  相似文献   

15.
An accurate self-adjusting CMOS $RC$ oscillator for capacitive and resistive sensor applications has been designed and manufactured. The oscillator operates with supply voltages from 1.2 to 3 V and achieves an internal accuracy of $pm$ 0.7% with a temperature range from $-20 ^{circ}hbox{C}$ to 60 $^{circ}hbox{C}$. The $RC$ oscillator was fabricated in a 0.35- $muhbox{m}$ standard n-well CMOS process with threshold voltages of 0.5 and $-$0.65 V. Its design and operation are described, and results of measurements performed on the fabricated chips are presented.   相似文献   

16.
A new process-an electron-"radiomagnetic" treatment-for obtaining high-remanence, low-coercive-force loops in magnetic alloys was recently announced. As an example, 2-MeV electron irradiation of 6-mil-thick ring laminations of polycrystalline 5-80 Mo Permalloy with 1017e/cm2in an applied circumferential magnetic field of 0.2 Oe atsim100degC produced record highs in remanence (∼6700 G) for this material. Additional studies of this process have been made to determine some of the controlling factors and the range of application. In particular, the effects of the dose (number of e/cm2) and of the preirradiation magnetic properties were examined. The results show that: 1) for a given dose of1.1 times 10^{17}2-MeV e/cm2, the relative change in remanence (DeltaB_{r}/B_{r}) is always positive, ranging from 10 to 50 percent, but varies inversely with the preirradiation value of remanence (Br); 2) for the same dose, the relative change in coercive force (DeltaH_{c}/H_{c}) also depends upon the preirradiation value of remanence, but in a different way. ForB_{r} < 5000G,DeltaH_{c}/H_{c}is either negative or zero. ForB_{r} > 5000G,DeltaH_{c}/H_{c}is positive, ranging from 20 to 150 percent, and increases linearly withB_{r}; 3) if the dose is reduced tosim0.8 times 10^{17}e/cm2, thenDeltaH_{c}/H_{c}is reduced to a tolerable level (∼10 percent) with no significant sacrifice in the positive gain in remanence and rectangularity. Hence, there are optimum dose ranges in the "radio-magnetic" treatments of alloys, where significant gains in remanence may be obtained without appreciable increases in coercive force.  相似文献   

17.
In a dc motor with permanent magnet stator, the mean no-load working point of the magnet material can, after stabilization by stall current, be represented by a pointB_{m},H_{m}on a recoil line inside the demagnetization curve. The point results from the application during stall of an effective mean field Hadue to armature reaction in addition to the self-demagnetizing field due to circuit reluctance. It is shown that the motor specification and sizes lead to a specific value forH_{m}/H_{a}. The limiting values of this ratio (Hmzero or Hazero) imply that the corresponding optimum magnet designs for minimum magnet volume should be based either on maximum recoil energy or on(BH)_{max}. In practice, the best extreme working point during stall should lie between the points for these two criteria, dependent on the actualH_{m}/H_{a}. In some existing motorsH_{m}/H_{a}has been found to be between 0.5 and 1.5. For such values ofH_{m}/H_{a}, the variation of Bmand ofB_{m},H_{m}with working point is illustrated for high coercivity ferrite and for two grades of cast alnico alloy. A note on design methods is appended  相似文献   

18.
《IEEE sensors journal》2010,10(2):235-242
This paper presents the modeling and simulation of a tin dioxide (${rm SnO}_{2}$) field-effect transistor (FET)-based nanobelt gas sensor. The model results are compared to numerical simulations and experimental data obtained from published results describing the fabrication of single crystal nanobelts grown through thermal evaporation techniques. The fabricated sensor shows good response when exposed to oxygen (${rm O} _{2}$) and hydrogen (${rm H} _{2}$) at room temperature. Gas adsorption causes changes in the electrical contacts due to oxygen vacancies in the bulk. As a result, the ${rm I}$ -${rm V}$ characteristics are very different when the device is exposed to (${rm O} _{2}$) versus (${rm H} _{2}$ ). In the presence of ${rm H} _{2}$, the behavior of the contacts is ohmic and saturation is caused by pinch-off of the channel at the drain contact. However, in the presence of ${rm O} _{2}$ , the behavior of the contacts is Schottky, and device saturation occurs at the source end of the device. Our model is based on a depletion mode MOSFET and it accounts for both ohmic and Schottky contacts when the device is exposed to oxygen or hydrogen. It also provides a possible explanation for the gate bias dependence of the saturation current seen in some published characterization data.   相似文献   

19.
Magnetic measurements were performed on amorphous (Fe, Ni)80B20, (Fe, Ni)80B19Si1, and (Fe, Ni)80P14B6alloy ribbons to yield the values of the magnetic moment per transition metal atom at 0 K and the Curie temperature. A close fit to the moment data, obtained by allowing not only the moments on Ni and Fe atoms to vary with Fe concentrationx, as revealed by neutron diffraction in crystalline alloys, but also the number of electrons per atom npand nbthat P and B atoms, respectively, donate to the transition metaldbands as described by the relationsn_{p} = 1.74 + 0.75 (1 - x)andn_{b} = 0.58 + 1.20 (1 - x), suggests a moment of 0 andsim0.13 mu_{B}per Ni atom in amorphous Ni80P14B6and Ni80B20alloys, respectively. The functional dependence of the Curie temperature onx, when followed closely for low Fe concentrations, gives the critical concentration xcabove which ferromagnetism appears in amorphous FexNi80-xB20and FexNi80-xP14B6alloy series asx_{c} cong 5and 8 at % Fe, respectively. The results of a theory based on coherent-potential approximation have been fitted to the measured values of Curie temperature in order to arrive at the Fe concentration dependence of the exchange interaction (JNiNi) between Ni-Ni pairs. The physical significance of the variation of JNiNiwithxobtained thereby has been discussed.  相似文献   

20.
A method was developed to design high-bandwidth single-ended variable-reluctance position sensors with high accuracy and extremely low temperature drift for use in magnetic bearing control systems. The method was used to design a hermetic radial position sensor with a position sensitivity ({1/L_{0}}{dL/dx}) of 1 percent/µm over the range of 0-50 µm and a temperature drift ({1/L_{0}}{dL/dT}) of less than 0.02 percent/°C over the range of 0-100°C, i.e., less than a 2-µm position error for a temperature variation of 100°C.  相似文献   

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