Quantifying Li-content for compositional tailoring of lithium ferrite ceramics

Owing to their multiple applications, lithium ferrites are relevant materials for several emerging technologies. For instance, LiFeO2 has been spotted as an alternative cathode material in Li-ion batteries, while LiFe5O8 is the lowest damping ferrite, holding promise in the field of spintronics. The Li-content in lithium ferrites has been shown to greatly affect the physical properties, and in turn, the performance of functional devices based on these materials. Despite this, lithium content is rarely accurately quantified, as a result of the low number of electrons in Li hindering its identification by means of routine materials characterization methods. In the present work, magnetic lithium ferrite powders with Li:Fe ratios of 1:1, 1:3 and 1:5 have been synthesized, successfully obtaining phase-pure materials (LiFeO2 and LiFe5O8), as well as a controlled mixture of both phases. The powders have been compacted and subsequently sintered by thermal treatment (Tmax = 1100 {\deg}C) to fabricate dense pellets which preserve the original Li:Fe ratios. Li-content on both powders and pellets has been determined by two independent methods: (i) Rutherford backscattering spectroscopy combined with nuclear reaction analysis and (ii) Rietveld analysis of powder X-ray diffraction data. With good agreement between both techniques, it has been confirmed that the Li:Fe ratios employed in the synthesis are maintained in the sintered ceramics. The same conclusion is drawn from spatially-resolved confocal Raman microscopy experiments on regions of a few microns. Field emission scanning electron microscopy has evidenced the substantial grain growth taking place during the sintering process - mean particle sizes rise from about 600 nm in the powders up to 3.8(6) um for dense LiFeO2 and 10(2) um for LiFe5O8 ceramics

FeCo Nanowire-Strontium Ferrite Powder Composites for Permanent Magnets with High-Energy Products

Due to the issues associated with rare-earth elements, there arises a strong need for magnets with properties between those of ferrites and rare-earth magnets that could substitute the latter in selected applications. Here, we produce a high remanent magnetization composite bonded magnet by mixing FeCo nanowire powders with hexaferrite particles. In the first step, metallic nanowires with diameters between 30 and 100 nm and length of at least 2 {\mu}m are fabricated by electrodeposition. The oriented as-synthesized nanowires show remanence ratios above 0.76 and coercivities above 199 kA/m and resist core oxidation up to 300 {\deg}C due to the existence of a > 8 nm thin oxide passivating shell. In the second step, a composite powder is fabricated by mixing the nanowires with hexaferrite particles. After the optimal nanowire diameter and composite composition are selected, a bonded magnet is produced. The resulting magnet presents a 20% increase in remanence and an enhancement of the energy product of 48% with respect to a pure hexaferrite (strontium ferrite) magnet. These results put nanowire-ferrite composites at the forefront as candidate materials for alternative magnets for substitution of rare earths in applications that operate with moderate magnet performance

Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process

[EN] The use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post-annealing at 1100 °C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage ≤ 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post-thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets.This work has been supported by the Ministerio Español de Ciencia e Innovación (MICINN), Spain, through the projects MAT2017-86540-C4-1-R and RTI2018-095303-A-C52, and by the European Commission through Project H2020 No. 720853 (Amphibian). C.G.-M. and A.Q. acknowledge financial support from MICINN through the “Juan de la Cierva” program (FJC2018-035532-I) and the “Ramón y Cajal” contract (RYC-2017-23320). S. R.-G. gratefully acknowledges the financial support of the Alexander von Humboldt foundation, Germany. A.S. acknowledges the financialsupport from the Comunidad de Madrid, Spain, for an “Atracción de Talento Investigador” contract (No. 2017-t2/IND5395)

Efectos del procesamiento cerámico y la adición de nanohilos de FeCo en la obtención de diferentes tipos de imanes permanentes de ferrita más sostenibles y mejorados.

La realización de este trabajo ha sido posible gracias a la financiación del Ministerio de Ciencia e Innovación de España a través de los Proyectos no. MAT2017-86450-C4-1-R, MAT2015-64110-C2-1-P, MAT2015-64110-C2-2-P, MAT2017-87072-C4-2-P, RTI2018-095303-B-C51, RTI2018-095303-B-C53, RTI2018-095303-A-C52 y FIS2017-82415-R y a través del Contrato Ramón y Cajal RYC-2017-23320; y por la Comisión Europea a través del Proyecto H2020 nº 720853 (AMPHIBIAN). El trabajo está financiado también por la Comunidad de Madrid a través del Proyecto S2018/NMT-4321 (NANOMAGCOST).Peer reviewe

Dense strontium hexaferrite-based permanent magnet composites assisted by cold sintering process

The use of rare-earth-based permanent magnets is one of the critical points for the development of the current technology. On the one hand, industry of the rare-earths is highly polluting due to the negative environmental impact of their extraction and, on the other hand, the sector is potentially dependent on China. Therefore, investigation is required both in the development of rare-earth-free permanent magnets and in sintering processes that enable their greener fabrication with attractive magnetic properties at a more competitive price. This work presents the use of a cold sintering process (CSP) followed by a post annealing at 1100 degrees C as a new way to sinter composite permanent magnets based on strontium ferrite (SFO). Composites that incorporate a percentage <= 10% of an additional magnetic phase have been prepared and the morphological, structural and magnetic properties have been evaluated after each stage of the process. CSP induces a phase transformation of SFO in the composites, which is partially recovered by the post thermal treatment improving the relative density to 92% and the magnetic response of the final magnets with a coercivity of up to 3.0 kOe. Control of the magnetic properties is possible through the composition and the grain size in the sintered magnets. These attractive results show the potential of the sintering approach as an alternative to develop modern rare-earth-free composite permanent magnets.(c) 2022 The Author(s). Published by Elsevier B.V. CC_BY_NC_ND_4.

Improvement of the magnetic properties of SrFe12O19 ceramics by tailored sintering with SiO2 addition

[EN] In order to obtain competitive strontium ferrite sintered magnets, SiO2 and CaO are added to avoid exaggerated grain growth. Besides favoring proper densification, these additives prevent the collapse of coercivity associated to grain growth. However, these additives may lead to slight decreases in density and the formation of paramagnetic α-Fe2O3 that hampers magnetization. Here, with the motivation of simplifying the production process, we present a study to maximize the magnetic performance of strontium ferrite ceramics using silica as the sole additive. A microscopic study offers insights into the grain growth mechanism activated by Silica. As a result, a compromise between relative density, coercivity and saturation magnetization is attained. It is found that sintering for 4 h up to 1200 °C with a SiO2 content of 1 wt% leads to the best compromise between coercivity, magnetization and density values. Competitive densities are reported in the absence of CaO, the usual co-additive. In addition, Confocal Raman Microscopy is employed for the first time to characterize the decomposition of strontium ferrite onto α-Fe2O3-Fe2O3.This work is supported by the Spanish Ministerio de Ciencia, Innovación y Universidades through Project no. MAT2017-86450-C4-1-R, RTI2018-095303-A-C52 and through the Ramón y Cajal Contract RYC-2017-23320 and Juan de la Cierva Program FJC2018-035532-I; and by the European Commission through the H2020 Project no. 720853 (AMPHIBIAN)

Greener processing of SrFe12O19 ceramic permanent magnets by two-step sintering

With an annual production amounting to 800 kilotons, ferrite magnets constitute the largest family of permanent magnets in volume, a demand that will only increase as a consequence of the rare-earth crisis. With the global goal of building a climate-resilient future, strategies towards a greener manufacturing of ferrite magnets are of great interest. A new ceramic processing route for obtaining dense Sr-ferrite sintered magnets is presented here. Instead of the usual sintering process employed nowadays in ferrite magnet manufacturing that demands long dwell times, a shorter two-step sintering is designed to densify the ferrite ceramics. As a result of these processes, dense SrFeO ceramic magnets with properties comparable to state-of-the-art ferrite magnets are obtained. In particular, the SrFeO magnet containing 0.2% PVA and 0.6% wt SiO reaches a coercivity of 164 kA/m along with a 93% relative density. A reduction of 31% in energy consumption is achieved in the thermal treatment with respect to conventional sintering, which could lead to energy savings for the industry of the order of 7.10 kWh per year.Spanish Ministerio de Economía y Competitividad through Projects no. RTI2018-095303-A-C52 MAT2017-86450-C4-1-R, MAT2015-64110-C2-1-P, MAT2015-64110-C2-2-P, FIS2017-82415-R and through the Ramón y Cajal Contract RYC-2017-23320; and by the European Comission through Project H2020 no. 720853 (AMPHIBIAN). V.Fuertes holds a Sentinel North Excellence Postdoctoral Fellowship and acknowledges the economic support from the Sentinel North program of Université Laval, made possible, in part, thanks to funding from the Canada First Research Excellence Fund

Boosting the coercivity of SrFe12O19 nanocrystalline powders obtained using the citrate combustion synthesis method

Strontium hexaferrite nanocrystalline powders were synthesized using a citrate combustion method and subsequently subjected to post-synthesis processing with the aim of tuning the micro-nanostructure to improve the magnetic properties. Firstly, the synthesis thermal treatments were optimized in order to minimize the formation of secondary phases, mainly hematite. Secondly, the as-synthesized powders were conditioned by a two-step process: ball milling in wet medium (ethanol) and high-speed mixing. The final processed powders exhibited a saturation magnetization of 74 emu g-1 and a coercivity of 6450 Oe. Following a low-temperature combustion synthesis, the coercivity is one of the largest values reported for strontium ferrites. The combination of the two-step conditioning procedure results in a useful methodology to obtain SrFe12O19 nanocrystalline powders with competitive properties. The morphological, structural and magnetic properties of the processed material make it a promising candidate for hard-soft ferrite-based composite magnets, where large coercivity values are highly desirable.This work is supported by the Spanish Ministerio de Ciencia e Innovación through Project Nos. MAT2017-86450-C4-1-R, RTI2018-095303-B-C51, RTI2018-095303-B-C53, RTI2018-095303-A-C52, and FIS2017-82415-R and through the Ramón y Cajal Contract RYC-2017-23320; and by the European Commission through Project H2020 No. 720853 (AMPHIBIAN). The work is funded as well by the Regional Government of Madrid through Project S2018/NMT-4321 (NANOMAGCOST). C G-M acknowledges financial support from MICINN through the ‘Juan de la Cierva’ Program (FJC2018-035532-I)

Influence of the growth conditions on the magnetism of SrFe12O19thin films and the behavior of Co/SrFe12O19bilayers

11 pags., 12 figs. 1 tab.SrFe12O19 (SFO) films grown on Si (100) substrates by radio-frequency magnetron sputtering have been characterized in terms of composition, structural and magnetic properties by a combination of microscopy, diffraction and spectroscopy techniques. Mössbauer spectroscopy was used to determine the orientation of the films magnetization, which was found to be controlled by both the sputtering power and the thickness of the films. Additionally, the coupling between the SFO films and a deposited cobalt overlayer was studied by means of synchrotron-based spectromicroscopy techniques. A structural coupling at the SFO/Co interface is suggested to account for the expetimental observations. Micromagnetic simulations were performed in order to reproduce the experimental behaviour of the system.This work is supported by the Spanish Ministry of Science, Innovation and Universities through Projects RTI2018- 095303-B-C51, RTI2018-095303-B-C53 and RTI2018- 095303-A-C52 (MCIU/AIE/FEDER,EU) and by the European Comission through Project H2020 No. 720853 (Amphibian) and by the Regional Government of Madrid through project S2018-NMT-4321. C.G-M. acknowledges financial support from MICINN through the “Juan de la Cierva” program (FJC2018-035532-I). Technical support of the technical staff of CIRCE beamline of the ALBA Synchrotron Light Facility is gratefully acknowledged

A simple vibrating sample magnetometer for macroscopic samples

We here present a simple model of a vibrating sample magnetometer (VSM). The system allows recording magnetization curves at room temperature with a resolution of the order of 0.01 emu and is appropriated for macroscopic samples. The setup can be mounted with different configurations depending on the requirements of the sample to be measured (mass, saturation magnetization, saturation field, etc.). We also include here examples of curves obtained with our setup and comparison curves measured with a standard commercial VSM that confirms the reliability of our device.Fil: Lopez Dominguez, Virginia Elena. Universidad Complutense de Madrid; España. Instituto de Ceramica y Vidrio de Madrid; España. Northwestern University; Estados UnidosFil: Quesada, A.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Guzmán Mínguez, J. C.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Moreno, L.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Lere, Martin Enrique. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; ArgentinaFil: Spottorno, J.. Universidad Complutense de Madrid; EspañaFil: Giacomone, Mariel. Universidad Complutense de Madrid; EspañaFil: Fernández, J. F.. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Hernando, A.. Universidad Complutense de Madrid; EspañaFil: García, M. A.. Universidad Complutense de Madrid; España. Instituto de Ceramica y Vidrio de Madrid; Españ