Papers by Keyword: Soft Magnetic Material

Abstract: The amorphous-forming ability (AFA) and the magnetic properties of the amorphous Fe-B-C-Si soft magnetic alloys have been investigated. Though the ternary Fe-B-C alloys exhibit high magnetization, their AFA is poor, which has prevented their practical application. It was confirmed that the addition of Si to the Fe-B-C alloys significantly improves AFA. Furthermore, it has been found that the composition range of the Fe-B-C-Si alloys with sufficient AFA can be identified by focusing on the enthalpy of mixing (ΔH_mix) and δ, which is related to the ratio of atomic radius between the constituent elements, of the alloys. The Fe-B-C-Si amorphous alloys that combine the high saturation magnetization of 175−177 A m²/kg with sufficient AFA to produce thick sheets whose thickness of 70 μm or more have been successfully developed by using the relationship between ΔH_mix, δ and AFA as a guideline. The Fe-B-C-Si amorphous alloys are expected to be applied to core materials for various magnetic components.

Abstract: The thermal and magnetic properties of the ternary Fe-B-C and quaternary Fe-B-C-Si amorphous alloys have been investigated. It has been discovered that the ternary Fe-B-C amorphous alloys with compositions close to Fe_79.3B_14.3C_6.4 exhibit a glass transition prior to crystallization on heating. The alloys also have high mass magnetization of 176–178 A m²/kg at room temperature. In addition, the glass-forming ability (GFA) of the alloys is significantly enhanced by the addition of 4 at% Si while maintaining high magnetization of approximately 170 A m²/kg at room temperature. In was found that the Fe₂₃(B, C)₆ phase (Cr₂₃C₆-type) is formed during crystallization of the quaternary Fe-B-C-Si alloys with the large GFA. It was also confirmed that the amorphous powders of Fe-Cr-B-C-Si alloys could be produced by a conventional water atomization method and exhibit the low core losses of 305–362 kW/m³ at 100 kHz and 100 mT. The quaternary Fe-B-C-Si amorphous alloys with high GFA, high magnetization and low core losses are suitable for a core material of various magnetic components.

Abstract: Surface structure and magnetic properties of thin films of the FINEMET-type alloy modificated by Mo (FeCuNbSiBMo) were studied in the aim of establishing of their dependence on heat treatment conditions. The thicknesses of the films were varied from 10 to 800 nm. Dependence of the microstructure of the films surface on the annealing temperature was analyzed using scanning probe microscopy. Parameters of the topography features were estimated as a function of the films thickness and annealing temperature. Magnetic hysteresis loops were measured using vibrating sample magnetometer and discussed in the focus of surface and thickness influences.

Abstract: Fe-Si alloy with a large Si content of 6.5 wt. % is obtained in nanocrystalline state by mechanical alloying of elemental iron and silicon powders. The mechanical alloying process was carried out using a high energy ball mill in argon atmosphere. Samples were collected after 0.5, 1, 2, 4, 6 and 8 hours of ball milling. The X-ray diffraction (XRD) studies indicate that after 4 hours of milling the Fe-Si alloy is formed. The powder magnetisation decreases upon increasing the milling time up to 4 hours as a consequence of the Fe-Si alloy formation. Upon heating, the DSC studies show the Fe₃Si compound formation in the samples milled for milling times lower than 6 hours. Also, the Curie temperature of the alloy was evidenced.

Abstract: Fe-Si alloy with a Si content of 10 wt. % was obtained in nanocrystalline state by mechanical alloying of elemental iron and silicon powders. The mechanical alloying process was carried out in a high energy ball mill (Fritsch, Pulverisette 4) in argon atmosphere. The X-ray diffraction (XRD) studies indicated that after 4 hours of milling the Fe-Si alloy is formed. The mean crystallites size decreases down to 7 nm after 8 hours of milling. The particles morphology investigated by scanning electron microscopy (SEM) showed an evolution during milling process from two different kinds of particles to a one kind of particles with irregular shape. The magnetisation of powders decreases upon increasing the milling time up to 4 hours as a consequence of the Fe-Si alloy formation.

Abstract: We report an investigation and a theoretical assessment of energy loss prediction in crystalline and amorphous soft magnetic materials. There were tested a sample made from non-oriented silicon iron (NO FeSi) M800-65A, industrial type alloy, cut longitudinally to the rolling direction and a toroidal sample of Co₆₇Fe₄B_14.5Si_14.5 amorphous ribbon. The losses behaviour of the crystalline NO FeSi strip was studied as function of frequency in the range of 5 Hz to 200 Hz at a given magnetic polarization (J_p) of 0.5 T and 1 T. In the case of the amorphous Co-based ribbon the losses variation was studied as function of frequency in the range of 5 Hz to 10 kHz at a given magnetic polarization of 20 mT. Using the concept of loss separation for the data analysis, in the approximation of linear magnetization law and low frequency limit, it can be considered in both cases, that the excess losses can be quantitatively assessed within the theoretical framework of the statistical loss model based on magnetic object theory.

Abstract: A highly sensitive open sample measurement system for soft magnetic strips, ribbons and films is described. It is a system built on a PXI platform combining PXI modules for control signal generation and data acquisition. The physical signals are digitized and the respective data streams are processed, presented and recorded in LabVIEW 7.0.

Abstract: Thermal processing of materials in external magnetic field is employed in order to produce a controllable uniaxial anisotropy and to tailor a domain structure in the series of soft magnetic FeCo-and FeNi-based amorphous/nanocrystalline alloys. Examples of our recent work on the utilization of both longitudinal and transverse magnetic field annealing for tuning the shape of hysteresis loops as well as the giant magnetoimpedance (GMI) characteristics are briefly presented. The beneficial effects of a heat treatment under magnetic field are discussed in terms of the improved application-oriented properties of these soft magnetic alloys.

Abstract: The effect of B₂O₃ fluxing on the glass-forming ability (GFA), the structure and the soft magnetic properties of Fe (-Co)-B-Si-Nb bulk metallic glasses (BMGs) has been investigated. The large Fe-Co-B-Si-Nb BMG specimens with diameters up to 7.7 mm, which is approximately 1.5 times as large as that of the maximum diameter of the copper mold cast one (= 5 mm), were prepared by the fluxing and water quenching. Thus the GFA of the Fe-Co-B-Si-Nb BMG are improved by the fluxing. It was confirmed that the soft magnetic properties of the Fe-Co-B-Si-Nb BMG are also improved by the fluxing. On the other hand, it was found for the Co-free Fe-B-Si-Nb BMG that the B₂O₃ fluxing promotes the precipitation of the α-Fe (-Si) and Fe₂B phases in the central region of the specimens; i.e., the GFA of the Fe-B-Si-Nb BMG is decreased by the fluxing. The Fe-B-Si-Nb BMG specimens show a flat hysteresis loop, indicating a good linear relationship between the magnetic induction and the applied magnetic field. These results of the Fe-B-Si-Nb BMG show that it is possible to develop a new soft magnetic material that exhibits constant permeability, which is necessary for producing inductors and choke coils.

Abstract: Magnetic properties, thermal stability and structure of the alloys - (Fe_0.6Co_0.4)₈₆Hf₇B₆Cu₁ (1), (Fe_0.7Co_0.3)₈₈Hf₇B₄Cu₁ (2) and (Fe_0.7Co_0.3)₈₈Hf₄Mo₂Zr₁B₄Cu₁ (3) obtained in the form of ribbons quenched from the melt were investigated after their nanocrystallization in the course of the thermal (TA) and stress (SA) annealings in the air at different temperatures. In all three alloys SA resulted in the induction of magnetic anisotropy with an easy axis along the direction of the ribbon. It is established that the alloy 3 after SA at 620°C for 20 min has the best thermal stability of magnetic properties, which remained practically unchanged after the subsequent annealing at 550°C for 26 hours. Magnetic properties of the alloys 1 and 2 subjected to SA under the same conditions did not change after annealing at 500°C.