MH Loops Research Articles

Study of Large Barkhauzen Sensor with Application of Step-like Giant Magnetoimpedance Element

A giant magneto-impedance element with step-like impedance properties was obtained for rectangular amorphous Co85Nb12Zr3 soft magnetic thin film with an in-plane uniaxial easy axis at approximately 60 degrees relative to the width of the element. This step-like impedance phenomenon occurred simultaneously with a change in the magnetic domain. We found through experiments that the magnetic field with changes in step-like impedance occurs had an almost constant value, with a standard deviation in the micro-tesla (μT) range, when an alternating magnetic field was applied. There is a possibility of applying this phenomenon to a large Barkhausen sensor with a constant magnetic field where a pulse signal appears. This paper reports a first trial where a step-like GMI element was applied to a large Barkhausen sensor. We present the results of measuring the MH loop for the step-like GMI element with resulting properties of a non-linear leap in magnetization, and also present the results of detecting a pulse signal by using a planar coil fabricated with the step-like GMI element. Some fundamental properties of the pulse signal are also reported, such as its form, variations in its height as a function of the frequency of the externa magnetic field, and variations in the pulse interval as a function of the frequency of the external magnetic field. We found that the domain change in the step-like GMI element is a kind of Barkhausen leap, and can be applied to a large Barkhausen sensor.

Rotation angle of magneto-optical Kerr effect with different capping layer on CoFe film

To understand the influence of rotation angle in magneto-optical effect between conductor and insulator capping layer, we fabricate Co 50Fe 50/Ta, Co 50Fe 50/MgO, and Co 50Fe 50/SiN x bilayers with fixed CoFe thickness and modulated capping layer to systematically study the dependence on the thickness and material of capping layer. We also changed the CoFe thickness with fixed Ta. The switching characteristics were studied using longitudinal magneto-optic Kerr effect (LMOKE) techniques. The hysteresis loops (MH loops) and the coercivity measured by AGM are independent of the capping layer. Our data show the Kerr rotation angle as a function of capping layer thickness. Based on our calculations, the effective rotation angle changes with different capping material. The phenomenon of the increasing Kerr rotation angle is known to be dependent on the dielectric constant and refractive index of the capping layer. A comparison between the rotation angle in LMOKE and the material property has led to a better understanding of the relationship of light refracted in Ta, MgO and SiN x .

Interface and magnetic characterization of FeCoV/NiO/FeCoV trilayers

The interface and magnetic properties of sputter-deposited FeCoV/NiO(tNiO)/FeCoV trilayers were analyzed by X-ray reflectivity, bulk magnetization, and polarized neutron reflectivity measurements. The layer depth profile, interface roughness, interface oxidation, etc. are obtained from specular X-ray reflectivity. The dc magnetization shows a coupled reversal of both FeCoV layers for tNiO < 20 nm, whereas for tNiO ≥ 20 nm, a step appears in the MH loop, which widens until tNiO reaches 40 nm. We investigated the magnetization state of the FeCoV layers during the magnetization reversal process by polarized neutron reflectivity measurements at selected points of the hysteresis loop. We conclude that the exchange coupling between the FM layers is accomplished by a spin twist mediated by the AF.

Ac MH loop measurements on Mn doped YBa2Cu3O7-δ superconductors

Isothermal ac MH (magnetization-field) loops for varying field amplitudes were recorded at 77 K on YBa2(Cu1-xMnx)3O7-δ with x = 0, 0.010, 0.015, 0.020, 0.025, 0.035 and 0.050, YBa2(Cuo.o75Fe0.025)3O7-δ, YBa2(Cu0.075Ni0.025)3O7-δ and YBa2(Cu0.075Zn0.025)3O7-δ samples up to a maximum field amplitude of 80 Oe. Flat band susceptibility, ac losses and flux profiles were deduced from the ac MH loops. The undoped sample exhibited a minimum weak link ac loss and the 5.0% doped sample showed maximum weak link ac loss. Ni and Fe doped samples showed higher granular losses.J cg estimated from the flux profiles decreases monotonically with increasing concentrations of Mn up to 2.5%.

Low power RF sputter deposition of oriented copper ferrite films

Thin copper ferrite films have been deposited on amorphous quartz substrates. The films are annealed in air and either quenched in liquid nitrogen or slow cooled from the annealing temperature. The quenched as well as slow cooled films, show (1 1 1) peaks of copper ferrite along with the (3 1 1) peak. This indicates strong (1 1 1) orientation of the films. From the MH loops, squareness value ( M R / M S ) has been calculated for both type of films. The squareness value of the parallel MH loop is double the value of the perpendicular MH loop.

High M/sub r/ squareness and exchange decoupled perpendicular recording media

CoCr/sub 15/Pt/sub 13/ perpendicular layers with CoCr-alloy/Ti dual underlayers were annealed and it was investigated how the dual underlayer structure influences the characteristics of the CoCrPt perpendicular layer. The Ti layer thickness has a remarkable influence on the Cr diffusion efficiency from the upper underlayer of the dual underlayer into the CoCrPt perpendicular layer. The Cr diffusion efficiency is improved by increasing the Ti layer thickness and the addition of Ta or Pt to the upper underlayer of the dual underlayer. As a result, the magnetic properties were greatly improved. For the CoCr/sub 15/Pt/sub 13/(40 nm)/CoCr/sub 30/Pt/sub 8/Ta/sub 2/(20 nm)/Ti(25 nm) media postannealed at 500/spl deg/C for 30 min., the coercivity and M/sub r/ squareness were 7100 Oe and 0.98 respectively. Also, the slope of the MH loop at coercivity was nearly 1/4/spl pi/.

High frequency, small signal MH loops of ferromagnetic thin films.

A method is presented for transforming the high frequency bias susceptibility measurements of ferromagnetic thin films into the form of a MH loop with, depending upon the measurement geometry, the y-axis zero crossing giving a measure of the coercive force or anisotropy field. The loops provide a measure of the quantitative and qualitative high frequency switching properties of ferromagnetic thin films.

Identification of the relation between the material parameters in the Preisach model and in the Jiles–Atherton hysteresis model

In this article the relation between the material parameters appearing in the Preisach model and those entering the Jiles-Atherton model is discussed. Emphasis is on the variation of the anhysteretic curve and on the magnetization dependency of the pinning parameter, when changing the Preisach distribution function. The discussion rests upon the consideration of the shape of the MH loop on the one hand and upon the identification of the instantaneous loss dissipation on the other hand. The techniques outlined are applied to silicon iron alloys and are compared with results from measurements.

Magnetoresistance and magnetic properties of Co/Ir multilayers on MgO(110) substrates

A Co(12 Å)/Ir(16 Å) multilayer deposited on MgO(110) is found to have a strong uniaxial anisotropy, comparable to bulk hcp-Co. Experimental results suggests the crystallographic relation of (100)[001]Co/(110)[001]Ir/(110)[001]MgO. A remarkable difference is seen between easy and hard axis magnetization processes, due to competition between the in-plane anisotropy and the exchange coupling. Considering the characteristics of the MH loops and magnetoresistance curves, we simulate the magnetization and magnetoresistance processes numerically. The results of our simulation indicate the existence of biquadratic coupling in Co/Ir(110).

垂直磁化膜におけるファンニングモードによる磁気機構の解析

To study the magnetic behavior in a perpendicular magnetic film, the magnetic energy density of the film is calculated on the assumption that the film is a three-dimensional array of ferromagnetic blocks. From the energy density, MH loop, the angular dependence of the coercive force He and the anisotropy field HK are calculated for the fanning and parallel rotation mechanisms. It is found that Hkf>Hcp>Hcf>Hkp,where f and p denote the fanning and parallel rotation mechanisms, respectively. These results for the fanning mode agree with many previous experimental results.

粒子間相互作用を考慮した媒体磁化モデル

A new medium magnetization model that takes account of the magnetic interaction of particles has been developed. It is based on the curling magnetization reversal model, and incorporates Atherton’s function for the mean field interaction. It is very easy to build the mean field function into the algorithm of our medium model. It was shown that the new medium model is very effective for fitting not only the MH loops but also the remanence characteristics of longitudinally oriented Ba-ferrite tape. It is expected that more precise simulation analyses will become possible through the use of this medium model.

Magnetization behaviors in a chain of disks

The magnetic behavior of a chain of N disks are investigated. The critical field Hcri for the discontinuous jump of the magnetization and the coercive force Hc for the fanning mechanism, and the uniaxial magnetic anisotropy constant Ku are estimated as a function of N, the aspect ratio of the disks, and the magnetocrystalline anisotropy constant K1. By comparing the MH loops calculated and the experiments, the values of K1 and N are obtained for an assembly with random orientation of Ba ferrite particles. This value of K1 agrees well with the experimental results obtained by Fujiwara [IEEE Trans. Magn. MAG-23, 3125 (1987)].

The magnetoresistivity, structure, and magnetic anisotropy of RF sputtered and E-beam evaporated NiFe films

Magnetoresistivity, magnetic hysteresis loop, and structure were studied on both RF sputtered (S-films) and E-beam evaporated (E-films) Ni81Fe19 films (4700 Å thick). The E-films were deposited on a rotating substrate (∼385 °C). The S-films were prepared on a stationary substrate with heat sinking. The room temperature magnetoresistivity (ΔR/R) were about 4.0% for E-films and about 3.7% for S-films. The ΔR/R differences for these two films resulted from higher resistivity of S-films. The structure of these films was investigated by TEM and X-ray techniques. The crystalline grain size was found to be 400 Å in diameter for S-films, and 800 Å in diameter for E-films. The x-ray diffraction patterns from a Read thin film camera revealed some preferred crystalline orientation for S-films. X-ray pole figures were taken for a closer measure of this texture. The results indicated that the S-films have (111) texture with their axes normal to the film plane. The magnetic properties for both films were observed with a MH loop tracer. Both films possessed low coercivity (about 1.5 Oe or less). The S-films were found to have in-plane magnetic anisotropy. Film stress and annealing effects were also studied. The differences of the observed resistivity and magnetic anisotropy for both films are attributed to an atomic ordering effect. The correlation of ΔR and texture is also discussed.

Structure-sensitive magnetic properties of RF sputtered NiFe films

X-ray small angle scattering (SAS) and transmission electron microscopy (TEM), together with MH loop measurements, were used to investigate effects of substrate bias on microstructural and magnetic anisotropy of sputtered NiFe films of 80-81 wt.% Ni. Films of ∼4000Å thickness had perpendicular anisotropy H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> ∼210 Oe when prepared with 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-6</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-7</sup> Torr base pressure and without bias, but MH loops showed no evidence of perpendicular anisotropy for bias voltages of -60V or more. SAS for these films correlated closely with values of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</inf> , being intense and anisotropic for 0V bias films but very weak for films sputtered with -60V or -120V bias. This correlation suggests that substrate bias for sputtered films and substrate temperature for evaporated films have similar effects on microstructure and magnetic anisotropy and that the magnetic anisotropy arises from magnetostatic interactions at aligned, crack-like voids. TEM observations were limited to films of 300Å-1300Å thickness. A strong void network and stripe domain pattern were seen only for 0V bias films prepared in poor vacuum. Improved vacuum conditions or application of -120V bias produced much more homogeneous films having in-plane domain structures for this range of thicknesses.