Magnetic oxides are promising materials for alternative health diagnoses and treatments. The aim of this work is to understand the dependence of the heating power with the nanoparticle (NP) mean size, for the manganite composition La_0.75Sr_0.25MnO₃ (LSMO)—the one with maximum critical temperature for the whole La/Sr ratio of the series. We have prepared four different samples, each one annealed at different temperatures, in order to produce different mean NP sizes, ranging from 26 nm up to 106 nm. Magnetization measurements revealed a FC-ZFC irreversibility and from the coercive field as function of temperature we determined the blocking temperature. A phase diagram was delivered as a function of the NP mean size and, based on this, the heating mechanism understood. Small NPs (26 nm) is heated up within the paramagnetic range of temperature ($T>T_c$), and therefore provide low heating efficiency; while bigger NPs are heated up, from room temperature, within the magnetically blocked range of temperature ($T<T_B$), and also provide a small heating efficiency. The main finding of this article is related with the heating process for NPs within the magnetically unblocked range of temperature ($T_c>T>T_B$), for intermediate mean diameter size of 37 nm, with maximum efficiency of heat transfer.

In this work the thermal expansion of $\mathrm{G}{\mathrm{d}}_5\mathrm{S}{\mathrm{i}}_{1.3}\mathrm{G}{\mathrm{e}}_{2.7}$ magnetic nanogranules was studied. A crossover from positive (macro- and microscale in the literature) towards a negative thermal expansion (at nanoscale) is observed. The negative thermal expansion (NTE) behavior was found in two temperature windows: 90–160 K $({\beta }^{\mathrm{LT}}\sim -32.2\mathrm{ppm}{\mathrm{K}}^{-1})$, and within the room temperature 255–340 K, where a giant NTE was observed $(-69\mathrm{ppm}{\mathrm{K}}^{-1})$. The key atomic mechanism driving the NTE is identified as an atomic triplet-chain flexibility. The results suggest that the NTE behavior emerges as a size-reduction effect caused by the intrinsic nanoparticles surface pressure (estimated at 11 kbar), leading to the positive thermal expansion–NTE crossover at the nanoscale.

The coupling between electric, magnetic and elastic features in multiferroic materials is an emerging field in materials science, with important applications on alternative solid-state cooling technologies, energy harvesting and sensors/actuators. In this direction, we developed a thorough investigation of a multiferroic composite, comprising magnetocaloric/magnetostrictive Gd $${}_{5}$$5 Si $${}_{2.4}$$2.4 Ge $${}_{1.6}$$1.6 microparticles blended into a piezo- and pyroelectric poly(vinylidene) fluoride (PVDF) matrix. Using a simple solvent casting technique, the formation and stabilization of PVDF electroactive phases are improved when the filler content increases from 2 to 12 weight fraction (wt.%). This effect greatly contributes to the magnetoelectric (ME) coupling, with the ME coefficient $${\alpha }_{ME}$$α M E increasing from 0.3 V/cm.Oe to 2.2 V/cm.Oe, by increasing the amount of magnetic material. In addition, magnetic measurements revealed that the ME-coupling has influenced the magnetocaloric effect via a contribution from the electroactive polymer and hence leading to a multicaloric effect. These results contribute to the development of multifunctional systems for novel technologies.

The so-called half-metallic magnets have been proposed as good candidates for spintronic applications due to the feature of exhibiting a hundred percent spin polarization at the Fermi level. Such materials follow the Slater-Pauling rule, which relates the magnetic moment with the valence electrons in the system. In this paper, we study the bulk polycrystalline half-metallic Fe2MnSi Heusler compound replacing Si by Ga to determine how the Ga addition changes the magnetic, the structural, and the half-metal properties of this compound. The material does not follow the Slater-Pauling rule, probably due to a minor structural disorder degree in the system, but a linear dependence on the magnetic transition temperature with the valence electron number points to the half-metallic behavior of this compound.