Rapid Secondary Recrystallization of the Goss Texture in Fe81Ga19 Sheets Using Nanosized NbC Particles

Herein, a simple and efficient method is proposed for fabricating Fe81Ga19 alloy thin sheets with a high magnetostriction coefficient. Sharp Goss texture ({110}<001>) was successfully produced in the sheets by rapid secondary recrystallization induced by nanosized NbC particles at low temperatures. Numerous NbC precipitates (size ~90 nm) were obtained after hot rolling, intermediate annealing, and primary recrystallization annealing. The relatively higher quantity of nanosized NbC precipitates with 0.22 mol% resulted in finer and uniform grains (~10 μm) through thickness after primary recrystallization annealing. There was a slow coarsening of the NbC precipitates, from 104 nm to 130 nm, as the temperature rose from 850 °C to 900 °C in a pure nitrogen atmosphere, as well as a primary recrystallization textured by strong γ fibers with a peak at {111} <112> favoring the development of secondary recrystallization of Goss texture at a temperature of 850 °C. Matching of the appropriate inhibitor characteristics and primary recrystallization texture guaranteed rapid secondary recrystallization at temperatures lower than 950 °C. A high magnetostriction coefficient of 304 ppm was achieved for the Fe81Ga19 sheet after rapid secondary recrystallization.

Improved Dynamic Magnetostriction measurement method based on M-EMAT for the characterization of residual strain

The Dynamic Magnetostriction (DM) measurement method as a nondestructive testing method of ferromagnetic materials, measures the DM curve using electromagnetic acoustic transducer (EMAT) to characterize material and predict the mechanical properties. Lorentz forces and magnetostriction forces contribute mainly to the ultrasonic generation. Only the range of low field, in which the magnetostriction force mechanism is predominant can be used to measure the DM curve, but the boundaries of this range are uncertain. The improved DM measurement method based on shear wave Magnetostriction EMAT (M-EMAT) is proposed and the theory of generation of shear waves is derived. For the M-EMAT, only magnetostriction force mechanism contributed to the generation of shear waves. A theoretical model for the optimization of the transducer is developed, the model is in good agreement with the experimental results. The microstructure changes caused by residual strain will affect the magnetostriction coefficient and the DM curve. Therefore, the DM curves of low carbon steel specimens with different levels of residual strains are measured by the optimized transducer to characterize the residual strain. The normalized results demonstrate that the slope of the DM curve obviously changes with the residual strain. This leads to the conclusion that the DM measurement method can be used to characterize the residual strain of the low carbon steels.

Effect of Al substitution for Ga on magnetostriction enhancement by annealing of as-cast Fe–Ga–Al alloys under low magnetic fields

Samples of Fe82Ga18-xAlx (1.5 £ x £ 15) alloys were prepared using a high vacuum arc melting system and homogenized at 1100 8C for 3 h, 1 000 8C for 120 h, and 730 8C for 168 h. The Fe82Ga18-xAlx(3 £ x £ 13.5) alloys were annealed at 550 8C for 15 min, while being exposed to a low magnetic field. The structure of the alloys was analysed by X-ray diffraction and optical microscopy. The magnetostriction coefficient of each of the samples was measured. It was found that the magnetostriction values of Fe82Ga18-xAlx(3 £ x £ 13.5) alloys were enhanced by magnetic field annealing. The magnetostrictive growth rate of the Fe82Ga15Al3sample was particularly large at 165%, and the Fe82Ga9Al9sample showed the highest magnetostrictive coefficient (up to 114 · 10-6) without compressive stress.

Unveiling hidden multipolar orders with magnetostriction

Broken symmetries in solids involving higher order multipolar degrees of freedom are historically referred to as “hidden orders” due to the formidable task of detecting them with conventional probes. In this work, we theoretically propose that magnetostriction provides a powerful and novel tool to directly detect higher-order multipolar symmetry breaking—such as the elusive octupolar order—by examining scaling behaviour of length change with respect to an applied magnetic field h. Employing a symmetry-based Landau theory, we focus on the family of Pr-based cage compounds with strongly correlated f-electrons, Pr(Ti,V,Ir)2(Al,Zn)20, whose low energy degrees of freedom are purely higher-order multipoles: quadrupoles $${\cal{O}}_{20,22}$$ O 20 , 22 and octupole $${\cal{T}}_{xyz}$$ T x y z . We demonstrate that a magnetic field along the [111] direction induces a distinct linear-in-h length change below the octupolar ordering temperature. The resulting “magnetostriction coefficient” is directly proportional to the octupolar order parameter, thus providing clear access to such subtle order parameters.

Compositional Design of Soft Magnetic High Entropy Alloys by Minimizing Magnetostriction Coefficient in (Fe0.3Co0.5Ni0.2)100−x(Al1/3Si2/3)x System

Developing cost-effective soft magnetic alloys with excellent mechanical properties is very important to energy-saving industries. This study investigated the magnetic and mechanical properties of a series of (Fe0.3Co0.5Ni0.2)100−x(Al1/3Si2/3)x high-entropy alloys (HEAs) (x = 0, 5, 10, 15, and 25) at room temperature. The Fe0.3Co0.5Ni0.2 base alloy composition was chosen since it has very the smallest saturation magnetostriction coefficient. It was found that the (Fe0.3Co0.5Ni0.2)95(Al1/3Si2/3)5 alloy maintains a simple face-centered cubic (FCC) solid solution structure in the states of as-cast, cold-rolled, and after annealing at 1000 °C. The alloy after annealing exhibits a tensile yield strength of 235 MPa, ultimate tensile strength of 572 MPa, an elongation of 38%, a saturation magnetization (Ms) of 1.49 T, and a coercivity of 96 A/m. The alloy not only demonstrates an optimal combination of soft magnetic and mechanical properties, it also shows advantages of easy fabrication and processing and high thermal stability over silicon steel and amorphous soft magnetic materials. Therefore, the alloy of (Fe0.3Co0.5Ni0.2)95(Al1/3Si2/3)5 holds good potential as next-generation soft magnets for wide-range industrial applications.

Effects of a Large Content of Yttrium Doping on Microstructure and Magnetostriction of Fe83Ga17 Alloy

As-cast (Fe0.83Ga0.17)100-xYx (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)17Y1.76 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 (Fe0.83Ga0.17)100-xYx alloys decreased sharply. The minimum magnetostriction coefficient is reduced to 12 ppm at the magnetic field of 426kA/m when x=9.

Fast Measurement of Magnetostriction Coefficients for Silicon Steel Strips Using Magnetostriction-Based EMAT

Strain gauges and optical methods are commonly used to measure the magnetostriction coefficient of a sample. All these methods require a specific size sample and can only realize offline measurement, which is time-consuming. Therefore, we propose a new method using a magnetostriction-based electromagnetic acoustic transducer (EMAT) to measure the magnetostriction coefficient. The amplitude of the ultrasonic waves generated by the EMAT is applied to characterize the magnetostriction coefficient of a sample. A nonlinear magnetostriction finite element model is established, and the simulation results show that the amplitude of the ultrasonic wave generated by the magnetostriction-based EMAT is proportional to the magnetostriction coefficient of the material. Experiments are carried out on silicon steel strips with different silicon contents. The results show that the method can effectively measure their relative magnetostriction coefficients. Furthermore, the structure of the magnetostriction-based EMAT is optimized to maximize efficiency. The excitation and receiving transducers reach their maximum efficiency when the static magnetic flux densities are 3.5 mT and 6.8 mT, respectively. Moreover, the relative error caused by the vibration reaches the minimal size when the lift-off of the receiving coil is set to 3 mm around. This method is fast and can be applied to online measurement.

Magnetic Domain Patterns in Bilayered Ribbons Studied by Magnetic Force Microscopy and Magneto-Optical Kerr Microscopy

The magnetic domain patterns of amorphous bilayered FeSiB/FeNbSiB and FeNbCuSiB/CoSiB ribbons are observed and analysed using the magneto-optical Kerr microscopy (MOKM) and magnetic force microscopy (MFM). Both microscopic techniques are highly sensitive to the sample surface; possibility of Kerr microscopy to visualize the domains separately in both layers is achieved by focusing the laser spot on the ribbon cross section. Wide curved domains as well as fine fingerprint domains were detected at the surface of ribbons due to presence of local stresses coming from the preparation process. With respect to high lateral resolution of MFM and its out-of-plane magnetization sensitivity, the perpendicularly magnetized crossed stripe domain patterns can be selected as well. Coiling of the ribbons on the half-round-end sample holder is often used to induce and control the magnetic anisotropy of these alloys. Changes in the magnetic domain structure at the outer-coiled surface and its dependence on the sign of magnetostriction coefficient are discussed in detail. Finally, the MFM images in the presence of external in-plane magnetic field up to ±40 kA/m are shown.

Enhancing the strain sensitivity of CoFe2O4 at low magnetic fields without affecting the magnetostriction coefficient by substitution of small amounts of Mg for Fe

Strain sensitivity is improved without affecting the magnetostriction coefficient upon substitution of a small amount of Fe by Mg in CoFe2O4.