Papers by Keyword: Magnetic Domain

Abstract: As-cast (Fe_0.83Ga_0.17)_100-xY_x (x=0, 3, 6 and 9) alloys were prepared by non-consumable vacuum arc melting furnace under a protective argon atmosphere. The crystal structures and surface morphologies of the alloys were studied by X-ray diffraction (XRD), optical microscope (OM) and scanning electron microscopy (SEM), combined with energy dispersive spectroscopy (EDS), respectively. The surface domain structures were observed by atomic force microscopy (AFM). The magnetostriction coefficients of the alloys were measured by strain gauging method. The results showed that the as-cast Fe₈₃Ga₁₇ alloy was composed only of a single phase of A2 with bcc structure, whereas the ternary Fe-Ga-Y alloys contain multiphase structure, besides the A2 phase, (FeGa)₁₇Y_1.76 new phases are observed as well, and an elemental yttrium phase appeared when the yttrium content increased to x=6 and x=9. Doping with yttrium have an effect on the change of magnetic domain structure of the binary alloy. With increasing x, the magnetostriction coefficient of the (Fe_0.83Ga_0.17)_100-xY_x alloys decreased sharply. The minimum magnetostriction coefficient is reduced to 12 ppm at the magnetic field of 426kA/m when x=9.

Abstract: Fe-Ga alloy is expected as energy harvest material having superior magnetostrictive properties. In this study, we compared angle dependence of amount of magnetostriction with ideal magnetostrictive model using cube-oriented single crystal Fe-18mol%Ga alloy. Magnetostriction in [100] of specimen was measured with changing the direction of statical magnetic field H by strain gauge. As a result, the measured magnetostriction could not fully explaind by traditional energy-based model of magnetostriction. We compared measurement result using strain gauge with calculation result using energy-based model. As a result, there was a large difference in maximum compressive strain value. We established modified energy-based model considering the deviation of magnetic domains so as to match the actual magnetostriction behavior.

Abstract: We carried out in situ tri-axial magnetostriction analysis for cube-oriented Fe-18%Ga single crystal by X-ray diffraction measurement under magnetic field. Periodic change in tri-axial magnetostriction with applied magnetic field direction was clearly observed. However, those values in [100] and [010] directions were not equivalent. Theoretical calculation of magnetostriction considering domain structure revealed this is caused by the non-equivalent volume fraction of initial magnetic domains.

Abstract: Magnetic Barkhausen noise (MBN) is a new technique on non-destructive testing of residual stress. The testing system based on virtual instrument was explored. It can achieve the MBN and deal with it in time. The technique is applied to analyze residual stress in the welding line of iron materials back and forth the heat treatment. Through comparing with the data of blind-hole method, the corresponding change between Barkhausen signals and residual stress is verified.

Abstract: The reversal process of an exchange spring trilayer was studied by micromagnetic simulation, simulating the hysteresis loop and magnetic domain wall structure of a soft/hard/soft ferromagnetic exchange spring. The exchange spring effect was observed, determining the chirality of its spiral magnetization configuration. By simulation of the domain wall structure, we find that reversal nucleation emerge simultaneously in either surface of two soft layers and the magnetic moments of hard layer start rotation at reversible stage.

Abstract: The experiment shows that the Magnetic Barkhausen Noise (MBN) signal strongly depends on the elastic deformation, heat treatment state of surface and microstructure of the material, etc. Using the MBN technology that rely on the material characteristics, MBN can be used for testing the surface hardness of 60kg/m U74 seamless rail made by China Harbin welded rail plant. And the testing result obtained by the MBN method is consistent with the results obtained by the Brinell hardness (HB) method. Consequently, this non-destructive testing technique will have a strong life and an extensive market.

Abstract: The microstructure and magnetic properties of melt-spun nanocomposite (Nd, Dy, Pr)-(Fe,Nb,Zr)-B /α-Fe ribbons have been investigated by XRD, SPM and VSM. The ribbons were prepared at a wheel speed range of 10-30 m/s. The multigrain domain or interaction domain was observed in the samples prepared at 20 m/s wheel speed. The easy magnetized direction c-axis parallel to the ribbon plane for the sample prepared at the wheel speed of 20m/s. The average gain size in this sample is about 18nm and the sample consists of hard magnetic phase (Nd, Dy, Pr) ₂(Fe,Nb,Zr)14B and sofe magnetic phase α-Fe, there is strong exchange-coupling interaction between them. The magnetic properties obtained are B_r=1.28T，H_ci= 504.2kA•m^-1，(BH)_max= 157.8 kJ•m^-3，M_r/M_s =0.76.

Abstract: We performed magnetic imaging of Ni-based ferromagnetic shape memory alloys. The magnetic microstructure was revealed by Lorentz microscopy and electron holography, which are powerful tools based on transmission electron microscopy. Observations of Ni51Fe22Ga27 and Ni50Mn25Al12.5Ga12.5 alloys, both of which have an L21-ordered structure in the parent phase, demonstrated that the antiphase boundaries (i.e., a type of planer defects) caused significant changes in the magnetization distribution due to depression of the atomic order—actually, the magnetization in these alloys depends upon the degree of chemical order. We propose a method which estimates the important magnetic parameters (the magnetocrystalline anisotropy constant and exchange stiffness constant) based on transmission electron microscopy observations. This method should be useful in magnetic measurements of nanometer-scale areas, for which conventional techniques cannot be applied.

Abstract: In this paper we present the results of investigation of spiral dynamic domains of a highly anisotropic iron garnet film with a perpendicular anisotropy in magnetic field with a constant dimensional gradient. The experiment showed how the presence of gradient of constant field affects the main parameters of spiral dynamic domains – geometrical form, life time, amount of orbits.

Abstract: In this paper it is presented a study of the magnetic anisotropy of non-oriented and grain oriented Fe-Si strips with the surface area of 280 x 30 mm2. The measurements were performed with a unidirectional single strip tester on Fe-Si strips cut at angles of 0, 15, 30, 45, 60, 75, 90 with the rolling direction. For the representation of the magnetic field strength at constant magnetic flux density it was used a program that interpolated the experimental results. It was determined the hard and the easy axis of the materials and the influence of the frequency on the anisotropy of the materials.