AC Magnetic Properties Research Articles

Magnetic properties of a melt-textured YBa2Cu3Ox ring with a perpendicular crack

The dc and ac magnetic properties of a melt-textured YBa2Cu3Ox ring with a perpendicular crack is studied. It is found that the crack behaves as a resistively shunted very long Josephson junction. However, besides the expected edge currents, certain inner currents have to occur in the junction. This anomaly may be a general feature of a very long junction with similar values of Josephson and London penetration depths, which is a case not yet studied theoretically.

Nano-particles of La0.9Ca0.1MnO3 manganite: Size-induced change of magnetic ground state and interplay between surface and core contributions to its magnetism

The structure, dc and ac magnetic properties of sonochemically prepared nano-particles of La0.9Ca0.1MnO3 compound were studied as compared to those of the bulk sample of the same composition. It is shown that transition to the nanometer sized scale results in a change of the magnetic order from a mixed antiferro+ferromagnetic to a pure ferromagnetic one due to the improvement of crystallinity and suppression of chemical/magnetic disorder in nano-particles. The surface contribution to its magnetism leads to a super-paramagnetic-like ordering supposedly due to the interfacial exchange coupling via surface tunneling of carriers above the Curie point (TC). Below TC∼90K, a notable contribution of surface spin disorder reduces the spontaneous magnetization of the nano-sample as compared to the bulk-one.

2419 高クロム鋼溶接継手の長時間高温強度に関する研究 : その8 電磁非破壊評価によるType-IV損傷検出性の検討(S13-2 高温材料・構造の強度と破壊(2),S13 高温材料・構造の強度と破壊)

The authors have discussed the feasibility of evaluation of Type IV damages of high Cr steel welds by electromagnetic nondestructive evaluation methods. As the first step, effects of isothermal-aging on magnetic properties were systematically examined. Ac magnetic properties at relatively high frequencies changes in accordance with Larson-Miller parameters of the isothermal-aging specimens of modified 9Cr-1Mo steel. Especially, ac losses at 100kHz correlate well with hardness of the specimens. Base on the findings, eddy current method was applied to the same samples. Signals linking the ac losses correlate well with hardness.

Comparative study of the sensing performance of orthogonal fluxgate sensors with different amorphous sensing elements

A comparative study of the sensing performance of orthogonal fluxgate sensors using different amorphous wires as sensing elements is presented. The sensing elements used are Co-based amorphous wire with and without glass-coating. The results show that the sensor with amorphous wire sensing element made by cold draw is more sensitive when the excitation ac passing through the wire is of low frequency, and the sensor with glass-coated wire is more sensitive when the excitation ac is of high frequency. The results are explained by considering the magnetic properties of the wires, such as the magnetic softness of the wires, indicated by the hysteresis loops, as well as by the magneto-impedance (MI) effect ratios that tell the ac magnetic properties of the wires under the influence of “skin effect”. The MI spectrum results show that the MI ratio of the cold-draw amorphous wire is larger at low frequency and smaller at high frequency, compared to that of the glass-coated wire, which reveals that the circumferential permeability plays a key role in the sensor sensitivity and the skin effect is related to the frequency characteristics.

AC magnetic properties of the soft magnetic composites based on nanocrystalline Ni–Fe powders obtained by mechanical alloying

Nanocrystalline soft magnetic composite materials based on nanocrystalline Ni 3Fe powder ( D=17 nm) and (Ni 3Fe+Fe) mixture have been produced by mechanical alloying. Composite materials have been prepared by covering the nanocrystalline particles with a dielectric polymer binder, then compacted into a toroidal shape and finally polymerized. The frequency dependence of the permeability and losses in the range 1–100 kHz and electrical resistivity were studied in correlation with the dielectric content, tores density and ferromagnetic powder type.

Glass-like and Verwey transitions in magnetite in details

We have measured low field DC and low frequency AC magnetic properties of single crystals of magnetite with continuously reading high-resolution SQUID magnetometer in temperature range from 5 to 150 K . The measurements show hysteresis of Verwey transition in temperature and linear opening of energy gap of about 40 meV above the transition. Below the transition an AC response may be well explained by a thermally activated charge hopping. For frequencies of the driving AC field close to the hopping frequency a spin glass-like behavior is observed. Extracted values of the energy gap, activation energy and attempt period agree with those found from infrared complex conductivity measurements. Characteristic temperature of the glass-like transition coincides with minimum of the spin–spin relaxation time observed by NMR with this sample. Both NMR and our data may be explained consistently on the basis of the fluctuation-dissipation theorem.

Size effects on the magnetic properties of Cu–Nb nanofilamentary wires processed by severeplastic deformation

We report on the influence of the microstructure on the AC and DC magnetic properties ofCu–3.5% Nb nanofilamentary wires. Samples obtained from a single Cu–3.5% Nb wire weresubsequently submitted to different plastic strain levels via drawing so that theirmicrostructure was altered. Noticeable differences are observed in their isothermal DCmagnetization curves that present a double-peak structure. The first peak, which occurs atlow magnetic fields, is attributed to superconductivity induced in the Cu matrix due to theproximity effect. It is argued that the second peak is related exclusively to niobium. Thedependence of these two distinct peaks on the characteristic nanometre length scales ofthe samples, i.e. dimension of the Nb filaments and interfilamentary spacing, arediscussed.

Magnetic properties of nanocrystalline Finemet alloys with Co addition

This report focuses on ac magnetic properties of (Fe 0.5Co 0.5) 73.5Cu 1Nb 3Si 13.5B 9 alloy in the high temperature. The effects of replacing 50% Fe by Co in Fe 73.5Cu 1Nb 3Si 13.5B 9 alloy on the static magnetic properties have also been studied. Addition of Co leads to an increase around 110 K of the Curie temperature of the amorphous phase, much higher than Ge-containing Finemet alloy. The material has much better ac magnetic properties than Hitperm alloy. An excellent stability of initial permeability in high temperature (up to 650 K) and high frequency (up to 5 × 10 5 Hz) can be observed with respect to the Co-free alloy.

Magnetic Properties of Fe-Based Ribbons and Toroidal Cores Prepared by Continuous Joule Heating Under Tensile Stress

Nanocrystallized Fe73.5Cu1Nb3Si 15.5B7 ribbons with controlled permeability were prepared by using continuous stress-annealing by Joule heating (CSA-JH) method. An optimization of the annealing conditions revealed that a completely developed anisotropy perpendicular to the ribbon axis can be obtained stably in the moving velocity range from 1 to 200 cm/min at the current density of 37.5 A/mm2. In particular, the highest velocity of 200 cm/min achieved the significant reduction in effective annealing time. The core made from the above-mentioned ribbon had good ac-magnetic properties such as constant permeability up to 2 MHz and low magnetic loss compared with those for different types of cores with controlled permeability. Consequently, it was clarified that the CSA-JH method is one of effective techniques for production of high performance toroidal cores with controlled permeability

高性能圧粉磁心材料の開発

Conventional soft magnetic materials used for various applications such as high-speed rotary motors were made by laminated steels. However, when these materials were used at high frequencies (1 kHz or higher), there was a decline in the magnetic properties caused by the core loss (heat generation by eddy current).To solve these problems, we developed new soft magnetic materials made of fine magnetic iron powder coated with an insulating layer, to which ultra-trace volume of heat-resistant binder is added with high density, thus obtaining superior magnetic properties using the powder metallurgy (P/M) method.This paper discussed on the DC and AC magnetic properties and the mechanical properties of newly developed P/M soft magnetic materials.

AC magnetic properties of bulk superconductor with FEM analysis and evaluation of exothermic phenomenon

AC magnetic properties of bulk high-temperature superconductor were evaluated with three-dimensional finite element method (FEM) analyses. When an external magnetic field strength increased, the heat was generated in weak link parts and the critical current density decreased greatly in these parts. The critical current densities in the weak link parts were estimated by experimental and analytical results under various external magnetic field strengths. The relation among the external magnetic field strength, the critical current density, and the heat generation were evaluated overall.

Magnetic Properties of Powdered Fe Cores Containing Stainless Steel-making Dusts

Effects of stainless steel-making dusts and binder content on compacting <TEX>$density(\rho)$</TEX> and magnetic properties were evaluated. Cores compacted with the mixture of pure Fe powders, <TEX>$5wt.\%$</TEX> dusts and <TEX>$0.25wt.\%$</TEX> binder showed good AC magnetic properties. For example, permeability<TEX>$({\mu}a)$</TEX> and core loss(P) of the cores containing <TEX>$5wt.\%$</TEX> dusts at 500 kHz were 62 and <TEX>$4008\;{\mu}W/cm^3$</TEX>, respectively. These properties are almost equivalent to those of competitor's products (i.e, Ancorsteel TC 80 produced by <TEX>$H\ddot{o}gan\ddot{a}s$</TEX> Corp.). The powdered cores obtained from the present work are expected to apply for high-performance soft magnetic components such as normal mode choke filter and pulse transformer.

High-temperature AC magnetic properties of FeCo-based soft magnets

The temperature dependence of AC magnetic properties of soft magnetic Co27Cr0.6Ni0.6Febal alloys has been studied. Microstructural characterization indicates that the alloy has a disordered BCC structure which is insensitive to heat-treatment. At low frequencies, the alloy shows a low coercivity Hc, high saturation magnetization Ms, and high magnetic permeability μm. As the frequency increases, all those properties deteriorate due to the damping of magnetic domain walls. On the other hand, Hc and Ms decrease, and μm increases with increasing temperature in the range of 20–600oC. The change of Hc and μm with temperature is attributed to the variation of magnetocrystalline anisotropy K1, which also improves the core loss at high temperature.

Effect of Tensile Stress and Texture on Magnetic Properties of FeCo Laminates

AC and dc magnetic properties and related losses of FeCo alloy sheet samples have been determined under applied tensile stress. Heat-treated strips of alloys Hiperco 50 Hiperco 50-HS and Hiperco 27 with three different orientations (0/spl deg/-45/spl deg/-90/spl deg/) with respect to the rolling direction were tested under tensile stresses up to 200 MPa. In our earlier work, we reported the effect of the compressive stress on the same alloy compositions . Unlike compressive stress, tensile stress decreased the coercivity and increased remanence of the alloys. For the 90/spl deg/-oriented Hiperco 50 alloy with a coercivity of 1.12 Oe under no applied stress, the minimum coercivity of 0.29 Oe occurred at about 100 MPa. The effect of tensile stress on the remanence was most pronounced in the Hiperco 50 HS samples. A gradual decrease in the coercive field of the three Hiperco 50 HS samples was observed up to 200 MPa. On the other hand, a minimum at 25 MPa is observed for the coercivity of Hiperco 27 samples. At the same tensile stress, the remanence ratio had a maximum. The 0/spl deg/-oriented sample exhibited the lowest core loss value of the Hiperco 27 samples.

Effects of substituting calcium for yttrium on the superconducting properties of YBa2Cu3Oz bulk samples

We report systematic studies of AC magnetic susceptibility and transport properties of Y1−xCaxBa2Cu3Oz bulk samples with 0⩽x⩽0.4. Single phase materials, reduction of carrier concentration and decrease of Tc to 83 K were obtained at doping levels up to 20%. For Y0.7Ca0.3Ba2Cu3Oz sample the improvement of grains boundary transport and screening capabilities has been observed as a result of the optimal ratio between carrier concentration and impurity phase BaCuO2 presence. The appearance of bulk pinning and nonlinear effects starting at the highest temperature were detected also.

Effects of substituting calcium for yttrium on the superconducting properties of YBa 2Cu 3O z bulk samples

We report systematic studies of AC magnetic susceptibility and transport properties of Y 1− x Ca x Ba 2Cu 3O z bulk samples with 0⩽ x⩽0.4. Single phase materials, reduction of carrier concentration and decrease of T c to 83 K were obtained at doping levels up to 20%. For Y 0.7Ca 0.3Ba 2Cu 3O z sample the improvement of grains boundary transport and screening capabilities has been observed as a result of the optimal ratio between carrier concentration and impurity phase BaCuO 2 presence. The appearance of bulk pinning and nonlinear effects starting at the highest temperature were detected also.

Structure and magnetic properties of amorphous and nanocrystalline Fe 40Co 40Cu 0.5Zr 9Al 2Si 4B 4.5 alloys

Crystallisation behaviour and magnetic properties of as-spun and annealed Fe 40Co 40Cu 0.5Zr 9Al 2Si 4B 4.5 alloy have been studied. The annealing was performed at 873 K for 15 min. XRD and TEM studies shows the formation of nanocrystalline α-(Fe,Co)(SiAl) particles with 7.5±2 nm in diameter dispersed in an amorphous matrix. The Curie temperature of the as-spun amorphous ribbon is 736 K. Saturation magnetisation of the annealed sample decreases at a rate of 0.5 emu/g/K in the measured temperature range of 300–1000 K. Excellent room temperature AC magnetic properties are achieved for the nanocrystalline sample. The low value of the imaginary part of the permeability and the high cut-off frequency (20 kHz) suggest that the eddy current contribution in the annealed materials is low. The coercivity of the annealed sample remains almost constant at 95 A/m up to the frequency of 20 kHz. High saturation magnetisation, high Curie temperature and excellent soft magnetic properties in the nanocrystalline state suggests that Fe 40Co 40Cu 0.5Zr 9Al 2Si 4B 4.5 alloy is a strong candidate for high temperature magnetic application.

Magnetic order in the lamellar compounds La1−Sr1+CoO4 (0⩽x⩽0.4)

Abstract We have studied the AC and DC magnetic properties of the lamellar compounds La 1− x Sr 1+ x CoO 4 (0⩽ x ⩽0.4). These materials are found to evolve towards an anomalous “cluster-glass”-like behaviour as x increases. The onset of the ferromagnetic order in the bidimensional phases is seen to occur at around 150 K, followed by a blocking process around 125 K. Also, present in the magnetic behaviour of these materials is the signal coming from small intergrowths of a perovskite phase, also detected by TEM, although invisible for powder-X-ray diffraction.

Structure and magnetic properties of high temperature nanocrystalline Fe–Co–Cu–Nb–Si–B alloys

High temperature nanocrystalline alloys were prepared by partial replacement of iron by cobalt in the Finemet type alloy. The (Fe 1– x Co x ) 73.5 Cu 1 Nb 3 Si 13.5 B 9 ( x =0.136–0.68) ribbons were obtained by melt-spinning technique and their chemical composition was determined by means of X-ray microanalyser. The effect of heat treatment, within the temperature range of 733–833 K, on magnetic properties of the alloys was examined. The structure of partially crystallized alloys was investigated using differential scanning calorimetry (DSC), X-ray diffractometry (XRD), and transmission electron microscopy (TEM). The AC (50 Hz) magnetic properties (coercivity, magnetic induction) of the Fe–Co–Cu–Nb–Si–B alloys were also studied. The effect of partial substitution of iron by cobalt on the structure and magnetic properties of the (Fe 1– x Co x ) 73.5 Cu 1 Nb 3 Si 13.5 B 9 alloys annealed in various temperatures and the thermal stability of magnetic properties of the alloys have been discussed.

Magnetic properties of melt-spun and annealed Fe62Co9.5Gd3.5Si10B15 alloy

The structural and magnetic properties of Fe62Co9.5Gd3.5Si10B15 alloy in as-spun and annealed states have been investigated. The presence of a nanocrystalline (Fe,Co)3Gd phase together with an amorphous phase in the as-spun ribbon was recognized. The primary crystallization of the amorphous phase occurred at 928 K. In spite of the presence of (Fe, Co)3Gd nanoparticles, the materials in the as-spun state exhibited a low coercivity of 2.74 A m−1 and the coercivity further reduced to 2.45 A m−1 after annealing at 773 K. The Curie temperature also increased with increasing annealing temperature. Excellent ac magnetic properties were also observed in the annealed specimen. The results indicate that the materials may be used for high frequency application. The good soft magnetic nature of the materials significantly deteriorated after annealing at temperatures above 823 K because of the precipitation of highly anisotropic B-rich phases.