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Pradeep K.G.,Max Planck Institute Fur Eisenforschung | Herzer G.,Vacuumschmelze GmbH and Co. KG | Choi P.,Max Planck Institute Fur Eisenforschung | Raabe D.,Max Planck Institute Fur Eisenforschung
Acta Materialia | Year: 2014

Rapid annealing (4-10 s) induced primary crystallization of soft magnetic Fe-Si nanocrystals in a Fe73.5Si15.5Cu1Nb 3B7 amorphous alloy has been systematically studied by atom probe tomography in comparison with conventional annealing (30-60 min). It was found that the nanostructure obtained after rapid annealing is basically the same, irrespective of the different time scales of annealing. This underlines the crucial role of Cu during structure formation. Accordingly, the clustering of Cu atoms starts at least 50 C below the onset temperature of primary crystallization. As a consequence, coarsening of Cu atomic clusters also starts prior to crystallization, resulting in a reduction of available nucleation sites during Fe-Si nanocrystallization. Furthermore, the experimental results explicitly show that these Cu clusters initially induce a local enrichment of Fe and Si in the amorphous matrix. These local chemical heterogeneities are proposed to be the actual nuclei for subsequent nanocrystallization. Nevertheless, rapid annealing in comparison with conventional annealing results in the formation of ∼30% smaller Fe-Si nanocrystals, but of identical structure, volume fraction and chemical composition, indicating the limited influence of thermal treatment on nanocrystallization, owing to the effect of Cu. © 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Bjork R.,Technical University of Denmark | Bahl C.R.H.,Technical University of Denmark | Katter M.,Vacuumschmelze GmbH and Co. KG
Journal of Magnetism and Magnetic Materials | Year: 2010

The magnetocaloric properties of three samples of LaFe 13-x-yCoxSiy have been measured and compared to measurements of commercial grade Gd. The samples have (x=0.86, y=1.08), (x=0.94, y=1.01) and (x=0.97, y=1.07) yielding Curie temperatures in the range 276288 K. The magnetization, specific heat capacity and adiabatic temperature change have been measured over a broad temperature interval. Importantly, all measurements were corrected for demagnetization, allowing the data to be directly compared. In an internal field of 1 T the maximum specific entropy changes were 6.2, 5.1 and 5.0 J/kg K, the specific heat capacities were 910, 840 and 835 J/kg K and the adiabatic temperature changes were 2.3, 2.1 and 2.1 K for the three LaFeCoSi samples respectively. For Gd in an internal field of 1 T the maximum specific entropy change was 3.1 J/kg K, the specific heat capacity was 340 J/kg K and the adiabatic temperature change was 3.3 K. The adiabatic temperature change was also calculated from the measured values of the specific heat capacity and specific magnetization and compared to the directly measured values. In general an excellent agreement was seen. © 2010 Elsevier B.V. All rights reserved.

Herzer G.,Vacuumschmelze GmbH and Co. KG
Acta Materialia | Year: 2013

This article surveys amorphous and nanocrystalline alloys for soft magnetic applications. Both materials have much in common, starting from the technique of production and including the key factors that determine their properties. Thus the magneto-crystalline anisotropy randomly fluctuates on a scale much smaller than the domain wall width and, as a consequence, is averaged out by exchange interactions so that there is no net anisotropy effect on the magnetization process, the prerequisite for good soft magnetic behaviour. Superior soft magnetic properties additionally require low magnetostriction, which is true of amorphous Co-based alloys and, more recently, nanocrystalline Fe-based alloys, but at a significantly higher saturation induction and with better thermal stability. Both materials reveal low losses of up to several hundred kilohertz and their B-H loop can be tailored by magnetic field annealing according to the demands of the application. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Dick C.P.,Cologne University of Applied Sciences | Polak C.,Vacuumschmelze GmbH and Co. KG | Waffenschmidt E.,Cologne University of Applied Sciences
IEEE Journal of Emerging and Selected Topics in Power Electronics | Year: 2015

In inductive wireless power transmission systems, often soft-magnetic shielding is used to avoid lossy eddy currents being induced in electrically conducting components like batteries or ground layers of electronic circuits. Datasheet information on such shielding materials are often limited to magnetic permeability and sometimes exemplary loss information. For designing inductive wireless power systems, e.g., at variable frequency, detailed loss information are of interest. Therefore, it is proposed to measure the impact of these materials on the power transmission in a standardized setup, which is closely related to the real application. This consists of two coils, a transmitting and a receiving coil. Here, a configuration as described in the Qi standard for wireless charging of mobile devices published by the wireless power consortium is used as reference. A figure of merit, i.e., the product of the coupling factor k and the geometric average of the coil's quality factors Q, is proposed to qualify materials concerning both: 1) shielding against conducting components on the backside of the receiving coil and 2) establishing a high mutual inductance of the transformer coils, resulting in higher system efficiencies. Furthermore, considerations on the measurement setup as well as qualifications of shielding materials are presented. © 2014 IEEE.

Suzuki K.,Monash University | Herzer G.,Vacuumschmelze GmbH and Co. KG
Scripta Materialia | Year: 2012

Realization of a high-saturation magnetization comparable to that of Fe-Si steel in advanced Fe-rich nanocrystalline soft magnetic alloys is potentially a very effective approach to reducing the emission of greenhouse gasses. This potential has stimulated recent research on the development of new alloys with exceptionally high Fe concentrations. However, some nanocrystalline soft magnetic alloys at the Fe-richest compositions exhibit unexpectedly large values of field-induced magnetic anisotropy (K u ∼ 100 J m -3) which have a detrimental effect on the exchange-softening process in the nanostructures. Our viewpoint is that much attention must be paid to the induced anisotropies in order to utilize the full potential of the exchange-softening effect in Fe-rich nanocrystalline alloys. Possible origins of the large K u value and the approach to suppressing the field-induced effect on K u are discussed. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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