Magnetostriction Changes Research Articles

Ｆｅ‐Ｍ‐Ｃ（Ｍ＝Ｔｉ，Ｚｒ，Ｈｆ，Ｖ，Ｎｂ，Ｔａ）膜の結晶化挙動

Microcrystalline Fe-M-C (M=Ti, Zr, Hf, V, Nb, Ta) films crystallized from amorphous state are suitable for use in magnetic heads. The crystallization of these films is supposed to be initiated by nucleation of fine M carbides because of the strong affinity of M for carbon. The precipitated Fe-rich phase was found to be a supersaturated solid solution which has a tetragonally deformed lattice, and it gradually changes to bcc phase as the annealing temperature increases. In these alloys, the change in soft magnetic properties with annealing temperature seems to be strongly affected by grain size rather than a change in crystal structure or magnetostriction. The coercivity increased at high anneling temperature caused by grain growth of Fe. The upper limit of annealing temperature is as high as 1000 K for Fe-Hf-C and Fe-Ta-C films which shows a relative high crystallization temperature.

Barkhausen effect and discontinuous magnetostriction in Terfenol-D

Measurements of magnetostriction λ, magnetic Barkhausen effect (MBE), and magnetic induction B have been made as a function of magnetic field H in a number of specimens of Tb0.3Dy0.7Fe1.9 prepared recently at Ames Laboratory. These results showed marked variations in properties from specimen to specimen. For example, the saturation magnetostriction of the materials under a compressive load of 14 MPa (2000 psi) varied from 1500 to 2200×10−6. However, it was noticed that in the high-performance, high-magnetostriction specimens a common feature was a very rapid change in magnetostriction with field in the range 400–500 Oe. Barkhausen measurements taken on two extreme specimens from the group also revealed very different signals, in particular the high-performance material was found to have a distinctive double peak in Barkhausen activity, one peak of which corresponded to the rapid change in magnetostriction, while the other occurred at the flat region of the magnetostriction versus field curve, corresponding to little or no change in magnetostriction.

Forced magnetostriction in amorphous Gd-Fe films

Composition and temperature dependence of forced magnetostriction have been measured for rf-sputtered Gd-Fe films using the cantilever capacitance method. Forced magnetostriction varies remarkably with film composition and temperature, and also depends on the substrate bias voltages applied during sputtering. It has been found that the change of forced magnetostriction coincides well with the change of the parameter δ, where δ is amount of fluctuation in the exchange constant between sublattice moment, and it has been evaluated by using Handrich’s modified molecular field theory. Therefore, we conclude that forced magnetostriction of sputtered Gd-Fe films is strongly related to δ.

Influence of the Tensile Stress on the Magnetostriction Resistivity and Magnetic Anisotropy of Co-Rich Metallic Glasses. TSRO and CSRO Correlation

The influence of tensile stress on the magnetic properties of amorphous alloys is reviewed for (CoFeNi) SiB compositions.(i) The compositional and thermal dependence of magnetostriction is examined as well as its evolution during structural relaxation. The close relation between the observed changes in magnetostriction and electrical resistivity after thermal annealing is pointed out. These results strongly suggest the existence of well defined chemical short range order, CSRO.(ii) The more remarkable characteristics of the anelastic anisotropy induced by stress annealing in the (Co1-xFex)75Si15B10 system are summarised. The compositional dependence of anelastic anisotropy was found to be surprisingly identical to the compositional dependence of the resistivity changes. These results indicate that a maximum degree of CSRO can be reached for the composition rate Co/Fe = 3.(iii) It was recently shown that the magnetostriction constant of some low-magnetostrictive metallic glasses linearly decreases with the applied tensile stress. The typical decreasing rate, dλs/dσ, ranges from −6 to −1 × 10−10 (MPa)−1.The origin of this experimental evidence is discussed by taking into account its relation with the stress induced anisotropy. Some new results dealing with the influence of the tensile stress on the electrical resistivity are also reported.

Relaxation parameters to simulate the changes in magnetostriction in amorphous magnetic alloys

We propose a method for deducing the parameters of the non-linear relaxation distribution model from isothermal measurements. Following this thermodynamic theory, isothermal relaxations can be described as isokinetic processes over a reduced time scale, taking into account non-linear effects, i.e. integrating the sample history. The proposed method leads to the definition of three characteristic parameters of this new time scale. In addition, the model predicts a universal shape of relaxation spectrum for frozen-in fluctuations. Applying this method to magnetostriction changes in Vitrovac® 6025 (Co 67Fe 4Mo 1.5Si 16.5B 11), we are able to simulate various thermal histories starting from high temperature equilibrium in the liquid state. We found good agreement with experiments. Free-energy spectra are determined.

Theory of ferromagnetic hysteresis: evaluation of stress from hysteresis curves

A recent extension of the theory of ferromagnetic hysteresis to include the effects of a constant applied stress uses an effective field H/sub sigma / that depends on the stress and the rate of change of magnetostriction with magnetization. The extended theory is used here to derive a particularly simple expression for the variation with stress of the anhysteretic differential susceptibility at M=O, H=O. The theoretical prediction is compared with experimental results and shows excellent agreement. This expression forms the basis for a novel technique of evaluating stress in ferromagnetic steels. >

Large Barkhausen discontinuity in (Fe1−xCox)-Si,B amorphous wire (abstract)

The magnetostrictive amorphous wires made by the in-water quenching technique have been shown to exhibit the large Barkhausen discontinuities,1 which make them attractive for sensor application.1 We reported earlier that the reentrant magnetic behavior of these wires is attributable to the magnetostrictive anisotropy caused by the residual stresses quenched in during solidification in the water.23 For further understanding of the magnetoelastic effect in amorphous wires, we measured the magnetic properties including the magnetic domain patterns for the in-water quenched (Fe1−xCox)-Si,B amorphous wires. The large Barkhausen discontinuity was observed only for wires having the positive magnetostriction. We found that the compositional variations of the width of labyrinthine domain and the critical field for reverse domain nucleation agree with those expected from the magnetostriction change with composition.

Flash annealing under stress in some Co-rich metallic glasses

Amorphous Fe 40 Ni 40 B 20 , (Co 95 Fe 5 ) 75 Si 15 B 10 (Co 88 Fe 12 ) 75 Si 15 B 10 , and (Co 89 Fe 11 ) 72 Mo 3 Si 15 B 10 ribbons have been annealed by means of short current pulses while a tensile stress was simultaneously applied. The temperature of the ribbons was determined by magnetic measurements and by using a thermocouple attached to the samples. In the temperatures between 300 and 500°C a perpendicular magnetic anisotropy is induced in the Co-rich glasses. The magnitude of this anisotropy varies with the annealing temperature and the thermal history of the sample. Changes in the saturation magnetostriction have been found in the (Co 95 Fe 5 ) 75 Si 15 B 10 alloy. The results are in overall agreement with those obtained by conventional annealing under stress.

Pressure changes and magnetostriction in finite magnetic fields in 3He and other normal fermi liquids.

Calculations of the change in pressure and magnetostriction which are exact to second order in the polarization are presented. From these effects it is possible to extract a combination of the linear field dependence of the Landau parameters and effective masses from a thermodynamic measurement in the normal phase of a Fermi Liquid.

Temperature dependence of magnetostriction in [Co 1− x(FeNi) x] 75Si 15B 10 amorphous alloys

Magnetostriction measurements as a function of temperature and composition are reported for [Co 1 x (Fe 0.5Ni 0.5) x ] 75Si 15B 10 metallic glasses. Single-ion as well as two-ion contributions to λ s are found in the composition range 0< x<0.5. For x=0.12 the magnetostriction changes sign with increasing temperature.

Dislocation drag mechanisms in normal state metals

Dislocation motion between barriers is determined by the electrons and phonons in metals of relatively high purity. This is especially true in the case of close packed metals such as copper or aluminum. At low temperatures, where the phonon density goes to zero, the electrons are the important components of the drag process, and the electron drag can be independently varied by a magnetic field. As the authors show, the change in stress from changing a magnetic field is solely related to the motion of dislocations, with such elementary considerations as magnetostriction and temperature change not being of importance. Furthermore, the experiements show that in the temperature range where the phonons become important, the change in stress with a change in magnetic field goes to zero. This is consistent with the dislocation motion, while travelling between barriers, being determined by the phonons present at that temperature. A straightforward explanation for this observation is that the phonons, with an increased density at the higher temperatures, are not affected by a magnetic field, and their increased density now controls the dislocation velocity. With this increased damping from the phonons the dislocations motion is no longer underdamped and as a consequence the magneticmore » field no longer affects the dislocation drag through the electrons. This and other experiments are described, as well as a discussion of the results in terms of the string model of a dislocation.« less

The influence of processing on magnetic and mechanical properties of Fe-B and Co-B metallic glasses

The influence of cooling rate on the mechanical and magnetic properties of Fe 85B 15, Fe 80B 20 and Co 79B 21 metallic glasses were investigated. In accordance with earlier results it was found that the microhardness decreases, and the tensile strength and bending number increase with the average cooling rate for Fe x B 1− x glassy alloys. The changes in hysteresis loop and the change in magnetostriction were correlated with the results of mechanical investigations.

Zero magnetostriction in amorphous Co-M-Nb alloys with high saturation magnetization

We have examined the dependence of magnetic properties of sputter-deposited amorphous Co-M-Nb alloys upon concentration of M (M = Mn, Fe, Ni, Ti and Mo). Particular interest is directed to the changes in saturation magnetization and magnetostriction (λ s ) of these alloys. It has been found that λ s in amorphous Co alloys with non-magnetic metals (Ti, Zr, Nb etc.) varies from positive to negative values through zero λ s as decreasing the atomic size of these metals. This behaviour is quite different from that of amorphous Co alloys with metalloids, in which λ s is always negative and insensitive to the kind of the metalloids Concerning the concentration trend, it is noted that the values of λ s are almost constant in the wide range of Nb concentration in spite of the large changes of saturation magnetization and the Curie temperature. The addition of Fe and Mn to Co 85 Nb 15 increases the saturation magnetization and meets zero magnetostrictive alloys in (Co 1-x M x ) 85 Nb 15 with M = Fe, Mn and x= 0.02 and 0.05, respectively.

Abatement of Electromagnetic Noise of Vaccum Interrupters

When a 3000A alternating current of commercial frequency (50 or 60Hz) flows to the central conductor in a vacuum interrupter (VI), a magnetostrictive noise of about 77dB(A) is generated on account of a magnetostrictive vibration of the metallic seal rings. From environmental considerations, the elimination of the VI noise is a pressing problem to be solved. In the newly developed low noise VI reported here, magnets have been bonded to the metallic seal rings. They produce a powerful magnetic field to saturate always the magnetic flux density in the ring so as to reduce or almost suppress a magnetostriction change. Repeating many experiments by this method, we have found an optimum condition and developed a 38dB(A) low noise vacuum interrupter at 3kA, 12kV.

On the influence of normal stresses on magnetostriction in (110)[001] silicon-iron sheet

An analysis is made of the system of stress and strain which occurs when a normal compressive stress is applied through an isotropic clamp plate to a silicon-iron crystal which is both magnetically and mechanically anisotropic. The effect of possible domain rotations between different <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\langle100\rangle</tex> axes on the relationships between stress and strain is determined, and hence the magnetostrictive energy changes which rotation would cause. It is thus shown that the effect on domain structure, and hence on magnetostriction, of normal stresses applied through glass, mild steel, or soft rubber differs significantly from the effect of a uniaxial stress. Stresses less than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> N/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> applied through thick glass or through steel tend to maintain the existing domain structure. The calculations also consider the effects of misoriented crystals, and some previously reported experimental results are discussed.

Ferrofluid hydrostatics according to classical and recent theories of the stresses

The hydrostatics of soft polarisable liquids is examined in the context of four ‘classical’ theories of the stresses in fluids, and of recent theoretical work which has resolved the controversy surrounding those theories. The classical stress systems predict various different internal pressures and magnetostrictive density changes, and only the stress system, based on energy, correctly gives the density change. The energy-based stresses proposed by Gans in 1904 generalise for nonlinear fluids the stress system of Helmholtz. All the stress systems predict the same surface variation of the pressure to contain a liquid, and they lead to a common surface-integral method useful for computing force on saturable iron bodies. The modern theories are represented, for equilibrium conditions, by a single and unique stress system which gives no information on internal forces. The meaning of the various ‘pressures’ found in the recent literature is discussed, and the role of density, rather than pressure, as the predictable mechanical variable inside a liquid is illustrated by a thought experiment.

NDRO plated wire preparation, stabilization, and aging

The literature describes plated wire suitable for nondestructive read-out (NDRO) memory operation, prepared from different NiFe electrolytes and process sequences. The NiFe films may be grouped into three categories based on the differences in their Ni-Fe composition fluctuation. In this paper, two types of NiFe electrolytes are studied. The development of NDRO characteristics is shown to require different processing for each electrolyte because of the differences in electrochemical behavior of the electrolytes and the metallurgical structures produced. The stabilization and aging of these films also depend on processing. The maximum temperature used for stabilization depends on the thiourea concentration in the NiFe bath and is independent of the nature of the substrate and the film thickness. Above this maximum temperature, changes in properties depend on the composition gradient in the film and on the differential thermal expansion between substrate and film. Magnetostriction changes during stabilization are observed and explained by interdiffusion with the substrate or homogenization of the film. These changes also reflect the different composition gradients of the films. Aging of wires decreases with decreasing concentration of thiourea; greater stability is shown to be most likely due to the large grain size and low impurity concentration of the NiFe films. Preliminary evidence from films made with saccharin containing electrolytes suggests that similar effects are present.

Effect of elastic stress on the magnetostriction of ferromagnets

An experimental study has been made of the effect of elastic tensile stresses on the magnetostriction curves of polycrystalline nickel, transformer steel, an equiatomic cobalt-platinum alloy, and an Invar iron alloy with 30–40 wt. % nickel. The sign of the magnetostriction changes during the rotation process under the effect of sufficiently high stress. The effect is explained on the basis of the concept of a magnetic “rotation” texture, developed earlier by one of the authors. A change in the magnetostrictive susceptibility for the paraprocess of the Invar alloy is found to be caused by the stress; the signs of the magnetostrictive constants are determined for the hardened cobalt-platinum alloy.

Magnetization and Magnetostriction of Hexagonal Cobalt Single Crystals with Internal Stresses

AbstractMeasurements of magnetization and magnetostrictive changes of the length were carried out on a plastically deformed cobalt single crystal at low magnetic fields. The results are in good agreement with theoretical calculations by Kronmüller et al. [1]. From this it is concluded that the magnetization processes within the closure structure of ferromagnetic domains at the crystal surface have no noticeable influence on the magnetization compared with the processes in the crystal volume.

Magnetoelastic Coefficient and Temperature Relationship in Thin Ni–Fe Films

Measurements of the magnetoelastic strain coefficient of nickel-iron thin films on soda-lime glass substrates have been made at temperatures from −40° to 200°C. The composition of the films ranged from 1% Ni rich to 1% Fe rich, with respect to the nonmagnetostrictive composition near 81% Ni, 19% Fe. Films with positive magnetostriction became less positive, and films with negative magnetostriction became less negative with a temperature increase. In some cases the magnetostriction changed from negative to positive when heated. The composition that displayed the least change in magnetostriction upon heating from −40° to 200°C is 0.1%. Fe-rich as compared to the nonmagnetostrictive composition. Changes in the coercive force and the anisotropy field with temperature are also reported.