Power saving has been a central driving force for the development of new materials. In this framework, soft magnetic composites appear as a feasible concept to be applied in strategic topics for modern society including sensing, energy generation, and conversion. With a unique freedom regarding material selection based on powder metallurgy techniques, this engineering magnetic material class allows novel designs able to drive operation conditions to new limits, unlocking the potential of novel applications. This document reviews soft magnetic composites by using a multidisciplinary approach addressing underlying physics responsible for their magnetic performance, limitations, and future trends.

Nanoparticles were prepared from a NdFeB-based alloy using the hydrogen decrepitation process together with high-energy ball milling and tested as heating agent for magnetic hyperthermia. In the milling time range evaluated (up to 10 h), the magnetic moment per mass at H = 1.59 MA m(-1) is superior than 70 A m(2) kg(-1); however, the intrinsic coercivity might be inferior than 20 kA m(-1). The material presents both ferromagnetic and superparamagnetic particles constituted by a mixture of phases due to the incomplete disproportionation reaction of Nd(2)Fe(14)BH(x) during milling. Solutions prepared with deionized water and magnetic particles exposed to an AC magnetic field (H(max) ~ 3.7 kA m(-1) and f = 228 kHz) exhibited 26 K ≤ ΔT(max) ≤ 44 K with a maximum estimated specific absorption rate (SAR) of 225 W kg(-1). For the pure magnetic material milled for the longest period of time (10 h), the SAR was estimated as ~2500 W kg(-1). In vitro tests indicated that the powders have acceptable cytotoxicity over a wide range of concentration (0.1-100 µg ml(-1)) due to the coating applied during milling.

The influence of the densification step, performed by uniaxial pressing at room temperature, on the coercivity μ ₀ H _c of NdFeB bonded magnets has been analyzed. The mass density does not play any role on μ ₀ H _c of non-cured magnets prepared by the mentioned method. Due to the brittle and intergranular character of the Nd ₂ Fe ₁₄ B-based phase fracture, the nano-sized grains are not affected or the modification is negligible, which maintains μ ₀ H _c unchanged. After curing, the intrinsic coercivity of the magnets is reduced as a function of the compaction pressure increase.

Expressions to simulate the intrinsic demagnetizing curve of permanent magnets are derived from the classical electrical analogy of a 2RLC circuit as an equivalent to a magnet under demagnetization in a closed magnetic circuit. Comparisons between experimental and theoretical intrinsic M x H curves were carried out for hard magnetic materials, and the possibility of using this analogous circuit with two components has also been investigated. The demagnetization curves of permanent sintered magnets have been simulated with time domain analytical expressions obtained using an electric equivalent circuit analogous to a closed magnetic circuit. This has been carried out for magnets measured at room temperature and at 373 K. Equivalent electric parameters influenced the various regions of the demagnetization curve. It has also been shown that it was possible to simulate the demagnetization curve of rare earth magnets and also other types of permanent magnets. The Stoner-Wohlfarth model theoretical curves have also been used as a comparison. At last, the electrical analogous parameters have been systematically varied in order to correlate them to the magnetic properties.