Efficient applications of magnetic cores in sensing and power electronics require low-loss and versatile soft magnetic materials, with excellent response on a wide range of frequencies. This objective is traditionally pursued with ferrite and Permalloy tape cores, available under a variety of properties. Comparable and even superior soft magnetic behavior can, however, be obtained with amorphous and nanocrystalline alloys, with the latter, in particular, combining flexible response to thermal treatments with high magnetic saturation. Broadband precise magnetic characterization of these materials, crucial to their use as inductive cores, is fully appreciated when associated with assessment by physical modeling. Comprehensive measuring approach and significant results obtained in sintered soft ferrites and nanocrystalline ribbons up to 1 GHz are highlighted in this paper. We show how broadband loss and permeability behaviors can be quantitatively interpreted in the framework of the loss separation concept, applied to eddy current and spin damping dissipation mechanisms.

We review the materials paradigm for metal amorphous nanocomposite (MANC) soft magnetic materials to showcase in solid state transformers (SSTs). We report 2D finite element analysis (FEA) of 3-phase SSTs operating at 50 Hz–10 kHz frequencies. We benchmark materials in designs to control high frequency losses and achieve higher power densities. FEA models are solved in the time domain for line frequencies of 50 Hz–10 kHz and 100 KW output power for the first 4 cycles. Transformer topologies are coupled to a power analysis using a Steinmetz parameterization of magnetic losses capturing induction and field scaling for transformer grade Si steel as compared to Metglas, Ferrite, FINEMET, Co- and FeNi-based MANCs. Recently discovered FeNi-based MANCs allow smaller transformers at equivalent power as compared to Si steel, Metglas, and Co-based MANCs. Fe-rich and non-Co containing MANCs also offer economies based on lower raw materials costs compared with Co-based MANCs.

We studied the effect of annealing on magnetic properties and structure of Heusler-type NiMnGa glass-covered microwires with a metallic nucleus diameter of about 22 μm prepared using the Taylor–Ulitovsky method. The as-prepared NiMnGa glass-covered microwires do not present ferromagnetic order at room temperature. Magnetization curves of the as-prepared samples do not present either saturation or coercivity at temperatures above 5 K. After annealing of the microwires, a ferromagnetic ordering is obtained with a Curie temperature of about 300 K which is beneficial for magnetic solid state refrigeration. The hysteresis observed on temperature dependence of magnetization in annealed samples and magnetic softening at about 260 K has been interpreted as the first-order phase transformation. Observed changes have been discussed considering internal stress relaxation after annealing, nanocrystalline structure of the as-prepared and annealed samples, recrystallization process and magnetic ordering of phases identified in the as-prepared sample and appearing under recrystallization. Existence of insulating and flexible glass-coating is beneficial for improvement of mechanical properties but the glass coating considerably affects magnetic properties of NiMnGa microwires. Therefore special attention must be paid to annealing conditions for realization of martensitic transformation.

Significant reductions recently seen in the size of wide-bandgap power electronics have not been accompanied by a relative decrease in the size of the corresponding magnetic components. To achieve this, a new generation of materials with high magnetic saturation and permeability are needed. Here, we develop gram-scale syntheses of superparamagnetic Fe/FexOy core–shell nanoparticles and incorporate them as the magnetic component in a strongly magnetic nanocomposite. Nanocomposites are typically formed by the organization of nanoparticles within a polymeric matrix. However, this approach can lead to high organic fractions and phase separation; reducing the performance of the resulting material. Here, we form aminated nanoparticles that are then cross-linked using epoxy chemistry. The result is a magnetic nanoparticle component that is covalently linked and well separated. By using this ‘matrix-free’ approach, we can substantially increase the magnetic nanoparticle fraction, while still maintaining good separation, leading to a superparamagnetic nanocomposite with strong magnetic properties.

The soft magnetic alloy Fe–Co–2V, also known as Permendur-2V or Hiperco® 50A, was subjected to equal channel angular extrusion (ECAE) at 750–850 °C using two processing routes. Hiperco is a trade name of Carpenter Technology Corporation. ECAE, which is a severe plastic deformation process, refined the grain size to about 1.5–3 μm, compared to 25–70 μm for the conventional Hiperco® bar. The fine-grain microstructure is homogenous throughout the ECAE material, from center to edge, due to the simple-shear ECAE process. Fine-grained Hiperco® has previously only been obtainable in the sheet form. ECAE resulted in yield and tensile strengths of 650–700 MPa and 900–1400 MPa, respectively, representing a 2–3-fold strength increase compared to the conventional bar. The yield strength was demonstrated to fit well to the Hall–Petch relationship established using previous reports on the strength of conventional bar and sheet materials. High ductility, up to 18%, was obtained in the ECAE processed billets and attributed primarily to the partially disordered bcc crystal structure upon quenching from ECAE.

In Part I, equal channel angular extrusion (ECAE) was demonstrated as a novel, simple-shear deformation process for producing bulk forms of the low ductility Fe–Co–2V (Hiperco 50A®) soft ferromagnetic alloy with refined grain sizes. Microstructures and mechanical properties were discussed. In this Part II contribution, the crystallographic textures and quasi-static magnetic properties of ECAE-processed Hiperco were characterized. The textures were of a simple-shear character defined by partial {110} and 〈111〉 fibers inclined relative to the extrusion direction, in agreement with the expectations for simple-shear deformation textures of BCC metals. These textures were observed throughout all processing conditions and only slightly reduced in intensity by subsequent recrystallization heat treatments. Characterization of the magnetic properties revealed a lower coercivity and higher permeability for ECAE-processed Hiperco specimens relative to the conventionally processed and annealed Hiperco bar. The effects of the resultant microstructure and texture on the coercivity and permeability magnetic properties are discussed.

The use of the advanced manufacturing technique of strain annealing for nanocomposite magnetic ribbons enables control of relative permeabilities and spatially dependent permeability profiles. Tuned permeability profiles enable enhanced control of the magnetic flux throughout magnetic cores, including the concentration or dispersion of the magnetic flux over specific regions. Due to the correlation between local core losses and temperature rises with the local magnetic flux, these profiles can be tuned at the component level for improved losses and reduced steady-state temperatures. We present analytical models for a number of assumed permeability profiles. This work shows significant reductions in the peak temperature rise with overall core losses impacted to a lesser extent. Controlled strain annealing profiles can also adjust the location of hotspots within a component for optimal cooling schemes. As a result, magnetic designs can have improved performance for a range of potential operating conditions.

The Fe–18.6% Ga alloy (at.%) has a high magnetostriction and an excellent piezomagnetic (PZM) property. However, Fe–Ga has a poor ductility and the addition of B helps to improve this property. The magnetostriction of the Fe–Ga alloy is not appreciably improved by the addition of B; however, the PZM behavior of Fe–Ga–B is unknown up to now. Then, an Fe–Ga alloy with 2% of B was produced to evaluate the effect of boron addition on the PZM property of the Fe–Ga alloy. The PZM force sensing performance coefficient d33* decreased, but the maximum sensitivity is reached for a fixed magnetic field. In addition, d33* values are among 2 and 5 mT/MPa, which is sufficient for many applications. A better ductility compared to Fe–Ga and a good sensitivity at constant field, makes the alloy Fe–Ga–B a good candidate for application as force sensors up to stresses of 80 MPa.

The influence of heat treatment (homogenization) on the microstructure, mechanical behavior, and soft magnetic properties of a face-centered cubic (fcc)-based high-entropy alloy (HEA), Fe29Co28Ni29Cu7Ti7, fabricated by casting, was investigated in detail. The as-cast Fe29Co28Ni29Cu7Ti7 HEA was composed of a primary fcc phase containing coherent dispersed L12 nanoprecipitates and trace amounts of a needle-like phase. The tensile yield strength (σ0.2), ultimate strength, and total elongation of the as-cast alloy are 917 MPa, 1060 MPa, and 1.8%, respectively. Following homogenization, the alloy having a single fcc phase shows a decrease of ∼ 55% in yield strength and a decrease of ∼ 36% in ultimate strength; however, the total elongation is increased from 1.8 to 52%. Saturation magnetization (Msat) is decreased from 111.54 to 110.34 Am2/kg, by contrast, coercivity (Hc) is increased from 266.65 to 966.89 A/m. The dissolution of precipitates and grain growth are mainly responsible for the changes in magnetic properties and mechanical behavior.

This article focuses on the finite element modeling of toroidal microinductors, employing first-of-its-kind nanocomposite magnetic core material and superparamagnetic iron nanoparticles covalently cross-linked in an epoxy network. Energy loss mechanisms in existing inductor core materials are covered as well as discussions on how this novel core material eliminates them providing a path toward realizing these low form factor devices. Designs for both a 2 μH output and a 500 nH input microinductor are created via the model for a high-performance buck converter. Both modeled inductors have 50 wire turns, less than 1 cm3 form factors, less than 1 Ω AC resistance, and quality factors, Q’s, of 27 at 1 MHz. In addition, the output microinductor is calculated to have an average output power of 7 W and a power density of 3.9 kW/in3 by modeling with the 1st generation iron nanocomposite core material.