This article provides a summary of the basic properties and the essential phenomenology of application‐oriented soft magnetic materials. Starting from an introductory section, where the magnetization process and the involved energetic aspects are highlighted, the physical rationale for the soft magnetic behavior of the materials is discussed, and a comparative illustration of their main physical, mechanical, and magnetic parameters is provided, the materials are classified according to their composition. We start from pure iron, the historical benchmark for any magnetic material, and pass through the selected alloys and compounds displaying the right combination of properties, including abundance of raw elements and costs, making them attractive for applications. We thus illustrate preparation methods, physical and magnetic properties, and applicative attributes of the following materials: (i) pure iron and low‐carbon steels; (ii) nonoriented and grain‐oriented Fe–Si alloys; (iii) High‐Si, Fe–Al, and Fe–Al–Si alloys; (iv) soft magnetic composites; (v) amorphous alloys; (vi) nanocrystalline alloys; (vii) Ni–Fe and Co–Fe alloys; (viii) soft ferrites. For each material, we summarize (i) compositional features and intrinsic physical and magnetic properties; (ii) metallurgical aspects and preparation techniques; (iii) magnetization process and magnetic hysteresis; (iv) energy losses and their dependence on the magnetizing frequency; (v) dependence of the magnetic properties on temperature and stress; (vi) mechanical properties; (vii) applications.

We report an investigation and theoretical assessment of the DC magnetic properties of high-permeability grain-oriented (GO) Fe-Si laminations under variously directed applied fields. We verified that normal magnetization curves, hysteresis loops, and energy losses depend on the field direction according to the sample geometry. This is explainable in terms of specific 180 and 90 domain wall processes and magnetization rotations. We present a novel phenomenological theory of the magnetization curves and hysteresis losses in GO laminations, excited along a generic direction; the theory is based on the single crystal approximation and pre-emptive knowledge of the magnetic behavior of the material along the rolling (RD) and the transverse (TD) directions. This approach is consistent with the general structure of Néel's phase theory, with the additional consideration of hysteresis and losses. Epstein and cross-stacked sheet testing methods are the two base measuring configurations; all the other testing geometries (single sheet, disk, square) are expected to display intermediate behavior. The devised model provides, through a direct procedure, thorough and accurate prediction of magnetization curves and quasi-static losses in these two basic cases. Its application to the other geometries is equally possible, with only a limited amount of supplementary information.

The sections in this article are Iron, Low‐Carbon Steels, and Silicon Steels Amorphous and Nanocrystalline Alloys Nickel‐Iron and Cobalt‐Iron Alloys Soft Ferrites

Magnetic losses under triangular symmetric and asymmetric induction waveforms have been measured over a broad range of frequencies and predicted starting from standard results obtained with sinusoidal induction. Non-oriented Fe-Si and Fe-Co sheets, nanocrystalline Finemet-type ribbons, and Mn-Zn ferrites have been investigated up to f = 1 MHz and duty cycles ranging between 0.5 and 0.1. The intrinsic shortcomings of the popular approach to loss calculation of inductive components in power electronics, based on the empirical Steinmetz equation and its numerous modified versions, are overcome by generalized application of the Statistical Theory of Losses and the related concept of loss separation. While showing that this concept applies both to ferrites and metallic alloys and extracting the hysteresis (quasi-static), excess, and classical loss components, we relate in a simple way the magnetic energy losses under symmetric triangular induction (square wave voltage) and sinusoidal induction. The loss behavior under asymmetric triangular induction is retrieved from the symmetric one, by averaging the energy losses pertaining to the two different semi-periods. Good comparison with the experimentally measured energy loss versus frequency behavior is demonstrated in all materials.

Extended frequency analysis of magnetic losses under rotating induction in soft magnetic composites J. Appl. Phys. 111, 07E325 (2012); 10.1063/1.3675177Cryogenic hysteretic loss analysis for (Fe,Co,Ni)-Zr-B-Cu nanocrystalline soft magnetic alloysWe report and discuss significant results on the magnetic losses and their frequency dependence in soft magnetic composites. Two types of bonded Fe-based materials have been characterized at different inductions from dc to 10 kHz and analyzed by extending the concept of loss separation and the related statistical theory to the case of heterogeneous materials. Starting from the experimental evidence of eddy current confinement inside the individual particles, the classical loss component is calculated for given particle size distribution. Taking then into account the contribution of the experimentally determined quasistatic (hysteresis) loss, the excess loss component is obtained and quantitatively assessed. Its behavior shows that the dynamic homogenization of the magnetization process with frequency, a landmark feature of magnetic laminations, is restrained in these materials. This results into a partial offset of the loss advantage offered by the eddy current confinement.

Nanoscale zerovalent iron (NZVI), promising for in situ degradation of many environmental contaminants, has been shown to aggregate reducing reactivity and mobility. Aggregation is attributed to the magnetic attractive forces between particles. In this study an alternating gradient force magnetometer (AGFM) is used to measure magnetic properties of NZVI. The magnetization curve is modeled according to the Langevin theory, evidencing a non-superparamagnetic nature of the particles. The measured ratio of remanent and saturation magnetization, 0.16, excludes the possibility of the dispersion being composed of Stoner-Wohlfarth (SW) type structures, probably due to the aggregated state of the particles at the measurement time. An extension of the Stoner-Wohlfarth model is therefore adopted to keep into account particle interaction and domain nucleation and found to be suitable for the system. Extended Derjaguin-Landau-Verwey-Overbeek (DLVO) model is applied to experimental data, under the hypothesis that primary particles behave according to the SW model, proving magnetic attraction to prevail on electrostatic repulsion.

A thermometric-fieldmetric method has been developed by which Fe-Si laminations are characterized under either alternating or rotational excitation up to peak induction B p = 1.85 T in the frequency range 2 HzՅ f Յ 200 Hz. The measurement is performed on circular samples ͑diameter= 140 mm͒ under digitally controlled one-dimensional/two-dimensional flux loci. The power losses at high inductions are determined by measurement of the rate of rise of the specimen temperature. Imperfect adiabatic behavior of the material is accounted for by physical modeling of the thermal diffusion process. The low-to-medium induction range, up to B p ϳ 1.7 T, is covered by conventional fieldmetric measurements, which, in conjunction with the thermometric approach, permit one to achieve a complete characterization of the magnetic sheets versus B p and f.

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