Saturation Magnetostriction Constant Research Articles

The influence of substrate on the magnetic properties of MnZn ferrite thin film fabricated by alternate sputtering

Mn0.5Zn0.5Fe2O4 film which has the highest saturation magnetization among Mn1–x Znx Fe2O4 thin films was prepared by the alternate rf sputtering method from two targets with compositions of MnFe2O4 and ZnFe2O4, respectively. The films were deposited on single-crystal Si(100), MgO(100) and SiO2/Si(100) substrates. The as-deposited films were amorphous, and after annealing in a vacuum furnace at 550 °C, polycrystalline MnZn ferrite films with residual amorphous matrix were obtained. The coercivity of all films is low, and the film on the MgO(100) substrate shows a coercivity as low as 27 Oe. The grain size of all films is about 20 nm and is less than the ferromagnetic exchange length (160 nm), so magnetic anisotropies are averaged to lower effective values. Furthermore, the negative magnetostriction constant of crystalline MnZn ferrite and the positive magnetostriction constant of amorphous Fe-based matrix will cancel out and may lead to a low or vanishing saturation magnetostriction constant. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Strong magnetoelectric coupling at microwave frequencies in metallic magnetic film/lead zirconate titanate multiferroic composites

Strong magnetoelectric coupling was observed at microwave frequencies in metallic magnetic film/lead zirconate titanate [Pb(Zr,Ti)O3] multiferroic composites, in which the magnetic films were either FeCoB or FeGaB with relatively high saturation magnetostriction constants between 40 and 70ppm and narrow ferromagnetic resonance linewidths of ∼20Oe at 10GHz. Large electrostatically induced ferromagnetic resonance frequency shifts of 50–110MHz at ∼2.3GHz were observed. These metallic magnetic film/Pb(Zr,Ti)O3 multiferroic composites with large electrostatic tunability of the ferromagnetic resonance frequency provide great opportunities for integrated microwave multiferroic devices.

Soft magnetism, magnetostriction, and microwave properties of FeGaB thin films

A series of (Fe100−yGay)1−xBx (x=0–21 and y=9–17) films were deposited; their microstructure, soft magnetism, magnetostrictive behavior, and microwave properties were investigated. The addition of B changes the FeGaB films from polycrystalline to amorphous phase and leads to excellent magnetic softness with coercivity <1Oe, high 4πMs, self-biased ferromagnetic resonance (FMR) frequency of 1.85GHz, narrow FMR linewidth (X band) of 16–20Oe, and a high saturation magnetostriction constant of 70ppm. The combination of these properties makes the FeGaB films potential candidates for tunable magnetoelectric microwave devices and other rf/microwave magnetic device applications.

Modified small angle magnetization rotation method in multilayer magnetic microwires

The small angle magnetization rotation (SAMR) technique is a widely used method to quantify magnetostriction in elongated ultrasoft magnetic materials. In the present work, we introduce significant optimization of the method, particularly simplification of the required equipment, profiting of the very peculiar characteristics of a recently introduced family of multilayer magnetic microwires consisting of a soft magnetic core, insulating intermediate layer and a hard magnetic outer layer. The introduced modified SAMR method is used not only to determine the saturation magnetostriction constant of the soft magnetic nucleus but also the magnetoelastic and magnetostatic coupling. This new method has a great potential in multifunctional sensor applications.

Study of Giant Magneto-Impedance Behavior in Co–Fe Based Amorphous/Nanocrystalline Materials

Giant magneto-impedance (GMI) behavior have been studied in melt spun Co71−XFeXCr7Si8B14 (X = 0, 2, 3.2, 4, 6, 8, and 12 at%) alloys. The addition of Fe in the system changed the saturation magnetostriction constant from negative to positive values. The GMI property was measured with a driving current of 5 mA and 4 MHz frequency using a spectrum analyzer. The GMI ratio increased with the increase of the applied dc field and became maximum at a field H k known as the anisotropy field of the materials. The maximum of GMI ratio (GMImax) depended on the Fe content and was maximum (12%) for Fe = 4 at% for the alloys in the as-melt spun state. Substantial increase of GMImax to 66% for Fe = 4 at% was observed after annealing the sample at 673 K.

Evolution of Barkhausen jumps in annealed amorphous wire having vanishing values of magnetostriction

A detailed study of the dc hysteresis loops for current and furnace annealed amorphous wires with vanishing saturation magnetostriction constant, λs, is reported. Measurements were conducted on wires of nominal compositions (Co0.94Fe0.06)72.5Si12.5B15 and (Co0.93Fe0.07)72.5Si12.5B15 which had λs values of similar magnitude but opposite sign. The results revealed the establishment and evolution of Barkhausen jumps at different points on the major hysteresis loops. These are interpreted on the basis of the core-shell domain model, widely used in the study of amorphous magnetic wires. The control of these jumps is essential for applications of wires where magnetic noise may be an issue. The influence of annealing conditions on the coercivity and susceptibility of the wires is also reported.

Temperature dependence of the magnetic anisotropy and magnetostriction of Fe100−xGax (x=8.6, 16.6, 28.5)

The temperature dependence of the lowest order magnetic anisotropy constant K1 and the lowest order saturation magnetostriction constant, (3∕2)λ100, were measured from 4 K to 300 K for Fe91.4Ga8.6,Fe83.4Ga16.6, and Fe71.5Ga28.5 and were compared to the normalized magnetization power law, ml(l+1)∕2. Fe91.4Ga8.6 maintains the magnetostriction anomaly of Fe (dλ100∕dT>0) and K1 is a reasonable fit to the ml(l+1)∕2 power law with K1(0K)≅90kJ∕m3. Fe83.4Ga16.6 does not show a magnetostriction anomaly, but fits the power law remarkably well. Fe71.5Ga28.5 possesses a small K1(∼1kJ∕m3) at all temperatures and a large temperature dependent magnetostriction, reaching ∼800ppm at low temperature.

Magnetocrystalline anisotropies and magnetostriction of ultrathin Fe films on GaAs with Cr overlayers

In this article we present data which show that Cr overlayers on epitaxial Fe films on GaAs substrates change the magnetic properties of the films in comparison to Au overlayers. For films thinner than 50 ML, the presence of the Cr overlayer reduced the magnitude of the uniaxial anisotropy in the Fe film, while for a 150 ML film, there was still a strong uniaxial anisotropy present. The anisotropy constants were determined using a modified energy density model, and were found to be smaller than those for Au overlayer films. The absolute magnetizations were measured on a vibrating sample magnetometer. It was determined that for the same thickness of Fe the magnetization with a Cr overlayer was 75% of that for a Au overlayer. This was either due to the Cr alloying with the Fe at the interface, or the Cr forming CrO2 on the surface of the film. The magnetostriction constant was determined using the Villari effect. For all the films the saturation magnetostriction constant was more negative than the bulk Fe value.

Magnetostriction effect of amorphous CoFeB thin films and application in spin-dependent tunnel junctions

CoFeB thin films and magnetic tunnel junctions using them are studied for magnetostriction effect. The single-layer films were sputter deposited with excellent soft magnetic properties including a high saturation magnetization of 1.5T, a near-zero hard axis coercivity, a low easy axis coercivity of 2.0Oe, and an induced magnetic anisotropy field of 32Oe. The saturation magnetostriction constant is measured to be 31ppm. Magnetic tunnel junctions (MTJs) were fabricated and tested for potential strain gauge applications. The gauge factor for the magnetostrictive MTJs, a measure of strain sensitivity, is many times of the best piezoresistive devices.

On the theory of electromagnetic fields radiated by an elastic wave in a ferromagnet

The generation of electromagnetic oscillations by a sound wave in a substance having magnetic order is investigated under conditions of the normal skin effect. The amplitude of the electric field and the phase difference of the electromagnetic and sound waves are calculated as functions of the saturation magnetization, anisotropy energy, magnetostriction constants, and other parameters characterizing the magnetic material.

Magnetostriction and magnetocrystalline anisotropy constants of ultrathin epitaxial Fefilms on GaAs, with Au overlayers

In this paper, we present the first measurements on the variation of the saturationmagnetostriction constant with film thickness of ultrathin epitaxial Fe films on GaAs(100)substrates. Furthermore, we explore whether there is a link between magnetostrictionand the uniaxial anisotropy in these Fe films. The Fe film thickness ranged fromseven monolayers (ML) (having only uniaxial anisotropy) to 50 ML (almost purecubic anisotropy). The anisotropy constants were determined from the normalizedmagnetization loops, using a magneto-optic Kerr effect (MOKE) fitting techniquethat convolutes a magnetic energy density model with the dependence of theMOKE signal on the angle between the pass plane of the analyser and the planeof incidence of the laser light on the sample. Each film was uniformly strainedalong the [011] direction, while the magnetization was measured along the direction using a MOKE magnetometer. From the change in anisotropy field as a functionof strain (Villari effect), the magnetostriction constant in the [011] direction was calculated.It is demonstrated that the saturation magnetostriction constant in the [011] direction issignificantly different to the equivalent value in bulk Fe, and increases in magnitude as thethickness of the Fe film decreases. It will also be shown that the uniaxial anisotropyconstant has a linear dependence on the magnetostriction constant for each film.

Effect of stress and/or field annealing on the magnetic behavior of the (Co77Si13.5B9.5)90Fe7Nb3 amorphous alloy

Variations of coercive field, induced magnetic anisotropy, and saturation magnetostriction constant in (Co77Si13.5B9.5)90Fe7Nb3 amorphous ribbons submitted to stress and/or axial magnetic-field annealing are reported. The annealing was carried out by using the Joule-heating effect (average temperature values of the sample corresponding to the intensity of the electrical current were 273, 378, 409, and 445°C) and the applied stress and axial magnetic field during the thermal treatments were 500MPa and 750A∕m, respectively. As a result of these treatments, a uniaxial in-plane magnetic anisotropy, which affects drastically the soft magnetic character of the samples, was developed.

Influence of Ni on the structural and magnetic properties of NixFe73.5−xSi13.5B9Nb3Cu1 (⩽x⩽25) alloys

A systematic investigation about the influence of Ni content on structure and magnetic properties of melt-spun NixFe73.5−xSi13.5B9Nb3Cu1 (0⩽x⩽25) alloys has been performed. The study has been done in amorphous ribbons as well as after thermal treatments leading to structure relaxation, to partial devitrification into nanocrystalline state, and finally to full structural crystallization. Different characterization techniques have been employed. Structure has been investigated by x-ray diffraction, differential scanning calorimetry, and Mössbauer technique, while magnetic properties as coercivity, saturation magnetostriction constant, or Curie temperature have been studied by induction methods. Two main behaviors have been distinguished depending on the Ni content of the alloys: (i) Low Ni content (up to x=15), when Ni atoms diffuse towards Fe sites in the disordered bcc (Fe,Ni)3Si structure originating reduced structural distortion and small changes in magnetic properties as coercivity and (ii) High Ni content (x=20,25) for which drastic changes are observed in structure (appearance of a tetragonal Fe3NiSi1.5 phase) and magnetic properties (coercivity increases up to two orders of magnitude) particularly after annealing at those temperatures for which optimum nanocrystalline structure is achieved for x=0.

Studies of the magnetoelastic inverse Wiedemann effect in pulsed laser depositedcylindrical cobalt films

Cylindrical soft magnetic Co films, nanostructured with a grain size of 1–2 nm and between and 90 nm in thickness, were produced by the pulsed laser deposition technique. Thesefilms showed a magnetostrictive property. The magnetoelastic inverse Wiedemann effect, orIWE, of longitudinal magnetization as a function of the circular applied magnetic field,Mz–Hϕ, was measured. The IWE made it possible to explain the magnetization processesaccording to an initial reversible rotation of the magnetization followed by magneticwall nucleation and propagation. A magnetization rotation model allowed us tocompare the reversible part and the first irreversible magnetization processescorresponding to the IWE. In this way, the values of the helical magnetic anisotropy,Kh, due to thehelical stresses, σh, generated by an applied torque to the films, were determined.A linear increase of the nucleating magnetic wall field,HN, with the appliedtorque, or with σh, was observed. In addition, the IWE made it possible to establishthe non-dependence of the saturation magnetostriction constant,λs, on the sample thickness and to determine the value of this negative isotropic .

Magnetostriction and surface roughness of ultrathin NiFe films deposited on SiO2

Ni 81 Fe 19 was sputter deposited onto Si single-crystal wafers which had the native oxide layer intact. Dc hysteresis loops were measured using the magneto-optic Kerr effect, and anisotropy fields determined from the susceptibility. Saturation magnetostriction constants were deduced from the change in anisotropy field as the samples were strained, using the Villari effect. The magnitude of the saturation magnetostriction constant λs of these polycrystalline films was observed to decrease as film thickness was reduced, but always remained negative in sign. Surface roughness was measured using an atomic force microscopy. By considering the variation of the magnitude of the saturation magnetostriction constant with a controlled level of surface roughness, we are able to rule out roughness as the cause of changes in λs as films decrease in thickness below 10–15 nm. This is an important further step in the understanding of the contribution of magnetoelasticity in the performance of soft magnetic films in read heads.

Surface, interface and bulk studies of NiFe nanometer films for magnetoresistive heads

Polycrystalline Ni81Fe19 films have been vapor-deposited in a forming field onto a 100-μm-thick borosilicate glass. The free surface and film/substrate interface magnetization has been probed using magneto-optical Kerr effect (MOKE) magnetometry, and bulk measurements have been taken using an alternating gradient force magnetometer. Saturation magnetostriction constants were derived from the strain dependence of the anisotropy field in the MOKE measurements, separating out for the first time free surface and interface effects. The free surface showed a clear uniaxial anisotropy with a low dispersion, while the interface showed a mixture of domain switching and moment rotation. We interpret the data in terms of a gradient in magnetic properties through the sample, and discuss consequences for magnetoresistive heads.

Determination of temperature dependence of saturation magnetostriction for Fe 81Si 3.5B 13.5C 2 amorphous film using strained substrate technique

Measurements of magnetostriction were performed at different temperatures for Fe 81Si 3.5B 13.5C 2 amorphous film using a bending method based on Villari effect. The magnetostriction constant was obtained from magnetic properties measured using a vibrating sample magnetometer. The quantity value of film strain is calculated from a special holder configuration. From the change of magnetic anisotropy field as a function of controlled strain, the saturation magnetostriction constant can be determined with sufficient accuracy. The temperature dependence of magnetostriction of amorphous Fe 81Si 3.5B 13.5C 2 film from 9 to 287 K is reported. It is suggested that a single-ion mechanism of magnetostriction is dominant in this amorphous alloy in a range of temperature considered.

Torsional impedance effect in Fe-rich amorphous wires

An amorphous ferromagnetic wire with a highly positive saturation magnetostriction constant, made of Fe 73.5Si 13.5B 9Nb 3Cu 1, was simultaneously submitted to both, an AC current flowing through it and a torsional stress, in order to induce a helical magnetic anisotropy that modifies the magnetic domain structure and therefore the magnetic response of the sample. We study the torsion-impedance effect in an Fe-rich amorphous wire when it is submitted to different applied torsional stresses in both senses, up to 0.8 π rad/cm, as a function of the drive current frequency, in the range of 10 Hz–2 MHz. The experimental results are explained on the basis of the core-shell magnetic structure model combined with the skin effect.

Origin of Low Coercivity of Fe-(Al, Ga)-(P, C, B, Si, Ge) Bulk Glassy Alloys

The magnetic properties of the glassy Fe-(Al, Ga)-(P, C, B, Si, Ge) alloys have been compared with those of the conventional Fe-based amorphous alloys to clarify the feature of the glassy alloys as a soft magnetic material. The glassy Fe-(Al, Ga)-(P, C, B, Si, Ge) alloys exhibit lower saturation magnetization (Js) than that of the conventional Fe-(B, Si, C) amorphous alloys with the same Fe content. The glassy alloys also have larger saturation magnetostriction constant (� s) than that of the conventional Fe-based amorphous alloys with the same Js. However, the

Magnetostriction of glass-coated Co-rich amorphous microwires and its dependence on current annealing

We present results on the saturation magnetostriction constant of four glass-covered Co-rich amorphous microwires for as-prepared and current annealed samples. The values of the saturation magnetostriction constant ( λ s) were obtained by using the small angle magnetization rotation method. The λ s data obtained in these magnetic materials are consistent with those previously reported in amorphous ribbons and wires with similar composition.