Structure and Magnetic Properties of Hot Pressed NiFe Powder

The aim of this work is to investigate the structure and magnetic properties of compacted microcrystalline NiFe (81 wt.% of Ni) powder. Bulk samples were prepared by compaction of milled NiFe (81 wt.% of Ni) ribbon. We found that after compaction of the powder displacement of domain walls becomes more dominant and the coercivity decreases and is comparable with the coercivity of conventional permalloy. The coercivity of the bulk material before heat treatment is lower than that for powder and that is why we can assume that the magnetic "contact" is restored after compaction. Annealing of bulk samples reduces the losses due to the relaxation of internal stresses induced by milling and compaction

AC Magnetic Field Effect on the Complex Permeability Spectra of Soft Magnetic Fe73Cu1Nb3Si16B7Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7} Powder Cores

In this work, two soft magnetic $Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7}$ powder core samples were investigated. Samples were prepared by milling of amorphous $Fe_{73}Cu_{1}Nb_{3}Si_{16}B_{7}$ ribbon at different temperature conditions: sample R, by milling at room temperature and sample L, by cryomilling at temperature of liquid nitrogen. Influence of applied exciting AC magnetic field with various amplitudes on the complex permeability spectra was studied. Obtained results are explained by the dynamics and relaxation phenomenon of domain walls under the influence of AC magnetic field

Low Frequency Core Losses Components of FeNiMo Powder Compacted Materials

The relations of core losses with the frequency of FeNiMo alloys were investigated. The core energy losses were determined by the measurements of dc and ac hysteresis loops as functions of frequency (1 Hz-50 Hz). The usual three-component concept of separation of core losses consisting of hysteresis, eddy current and anomalous losses was used to explain the influence of the powder particle size on core loss frequency dependences

The Role of Temperature on the Magnetization Process in CoFeZrB/FeCuNbMoSiB Hybrid Ferromagnets

The study presents magnetization process behaviour versus operating temperature up to 100°C in dual-phase ferromagnets in the light of their complex permeability spectra and energy losses from quasi-dc regime up to about 1 MHz upon defined peak induction. The samples consist of two Co- and Fe-based ball-milled-ribbon powders mixed in the same mass ratio. The magnetic characterization has been carried out by a digital hysteresisgraph-wattmeter using complex permeability approach to the linear material. Temperature invoked reduction of anisotropy leads to the decrease of hysteresis losses and significantly affects the low-frequency part of permeability and losses that is ascribed to domain wall movement. The high-frequency behaviour remains unchanged with respect to increase of temperature

Magnetic Properties of Crystalline NiFe Alloy Prepared by High-Energy Ball Milling and Compacting

The structure and magnetic properties of compacted microcrystalline NiFe (81 wt% of Ni) powder is investigated. The powder of NiFe alloy prepared by ball milling of ribbon (prepared by melt spinning) remains single phase material suitable for compaction in order to prepare soft magnetic material. The bulk samples were consolidated by uniaxial compaction of the powder in vacuum. By measuring of AC and DC magnetic properties it was found out that in bulk samples the displacement of domain walls is the dominant magnetization process, while rotation of magnetization vectors prevails in powder material

DC Magnetic Properties of Amorphous Vitrovac Ribbon

Soft magnetic amorphous Co-based materials prepared by rapid quenching method in the form of thin ribbon are well-known due to their excellent soft magnetic properties as high permeability, low coercivity, and low magnetic losses in kHz range. The amorphous Co-Fe-B-Si material Vitrovac® 6155 U55 produced by Vacuumschmelze GmbH & Co. KG belongs to this class of materials and was investigated in as-delivered state. The aim of this work was to study DC magnetization process by various experimental methods. We have measured magnetization curve by fluxmeter based hysteresis graph and hysteresis loops by three different fluxmeter based hysteresis graphs, exhibiting significant differences. The first and the second hysteresis graph perform the hysteresis loops measurement by the point-by-point method, either with commutative or with summing steps. The third one is AC hysteresis graph working at very low frequencies down to 7 mHz, performing the continuous method. The explanation of this result is based on the structural after effect influencing the domain wall displacement. We assumed that the domain structure consists of very small number of domain walls responsible for magnetization process, which was confirmed by the visualization of static domain structure by a computer-controlled setup based on the Kerr effect

The Influence of Preparation Methods on Magnetic Properties of Fe/SiO₂ Soft Magnetic Composites

An analysis of several variants of the Fe/polymer/SiO₂ composites in terms of the impact of iron powder particle shape (irregular, spherical), of the content (0.4-2.0 wt%), of the polymer type (shellac, thermoset SL450) and the method of its application as well as the effect of the preparation procedure of the composites (mixing and/or vacuum-pressure impregnation) on properties of electrical insulating layer (thickness and coherence), electrical resistivity and magnetic properties was carried out. It was found that the main governing factor of the microstructure formation is the shape, surface microgeometry of the iron particles and the insulator layer. These determine not only the uniformity of thickness and cohesion of the insulating layer of the applied polymer or its hybrid modification (polymer+SiO₂ nanoparticles), but also the most suitable method of preparation in terms of the achieved values of electrical and magnetic properties of the composites

Preparation and Characterization of Fe/SiO2SiO_{2} Powder Composites Using Impregnation Method

Fe/$SiO_{2}$ powder composite materials based on irregularly and/or spherically shaped iron powder particles with an addition of $SiO_{2}$ nanopowder were prepared in two ways, (i) by mixing the Fe/$SiO_{2}$ powder with 1.0 wt.% of Shellac dissolved in ethanol and (ii) by vacuum/pressure impregnation of low-temperature sintered Fe/$SiO_{2}$ components with shellac dissolved in ethanol and with thermoplast SL450. $SiO_{2}$ was implemented either as nanopowder or by sol-gel coating. Vacuum/pressure impregnation (VPI) of pre-sintered samples was performed in a steel container. The influence of iron particle shape and processing conditions on the electro-insulating layer was microscopically evaluated and correlated with the values of the electrical resistivity and coercivity. It has been found that the continuity, distribution and thickness of insulating phase is strongly controlled by the shape of iron particles. Using the VPI procedure, the irregular surface of iron particles may cause discontinuities of insulating layer, while the spherical iron particles are well covered with continuous evenly distributed insulating layer

Influence of Film Thickness on the Microstructure and Magnetic Properties of Finemetic Thin Films

The aim of this work was to study the influence of film thickness on the structure and magnetic properties of finemetic thin films after annealing. Thin films with the various thickness (from 20 nm up to 700 nm) were prepared by DC sputtering method. The heat treatments of the films for further structural and magnetic observations were performed at the temperature range 300-500°C for 15 min in vacuum furnace. Structural observations were carried out by transmission electron microscopy. Coercivity was determined from hysteresis loops traced with fluxmeter and Kerr magnetooptical hysteresisgraph. All the experimental results confirm a different magnetic behaviour of the thin films according to their thickness

Isobaric Thermal Expansion and Isothermal Compression of Powdered NiFe Based Alloys Studied by In-Situ EDXRD

The aim of the present work was to study the isothermal compression and isobaric thermal expansion behaviour of ball-milled NiFe (81 wt.% of Ni) and NiFeMo (79 wt.% of Ni, 16 wt.% of Fe) alloy and follow its phase evolution when exposed to high pressure and temperature. In-situ pressure-temperature energy dispersive X-ray (EDXRD) diffraction experiments were performed at the MAX80 instrument (beamline F2.1). The compressibility of NiFe alloy at 400 °C was evaluated for pressure values of up to 3.5 GPa. The EDXRD spectra revealed the presence of cubic FeNi_{3} phase as determined from the shift of (111), (200) and (220) reflection lines in corresponding EDXRD spectra