Designing Co Fe nanocrystalline powders for powder metallurgy and soft magnetic applications: Phase evolution, defect structuring and magnetic performance engineering

Soft magnetic applications in the RF range

Potential suitability of NiO-CuO nanocomposite for photoconductive sensor, soft magnetic materials applications and as antimicrobial agent

Hierarchicalnickel nanowires (h-NiNWs) were synthesized by a simplereduction method and their electrical, magnetic, and electromagneticcharacteristics were investigated. These nanowires possess a highmagnetic saturation (Ms) of 51 emu/g andalso a coercivity (Hc) of 34.5 Oe, whichmakes them suitable for soft magnetic sensor applications. Hall transportis being reported for the first time for h-NiNWs, and electrical conductivityat room temperature was studied to assess their applicability as aHall sensor wherein the Hall coefficient RH was found to be −1.39 × 10–12 Ωcm/Oe. Electromagnetic characterization of synthesized h-NiNWs showsexcellent microwave shielding effectiveness of above 24 dB for theKu band (12.4–18 GHz) and a maximum value of 32 dB at 14 GHzfor a sample with a thickness of about 1 mm. A room-temperature-curablescreen-printable ink was formulated using the synthesized magneticnanostructures and printed on different flexible substrates. Printedpatterns show promising ferromagnetic properties, and they could bepotential candidates for soft magnetic sensor applications.

Friction consolidation of gas-atomized Fe[sbnd]Si powders for soft magnetic applications

There is a growing interest on the soft magnetic thin-film applications in the GHz frequency range based on the development of new magnetic thin-film materials as well as the need of miniaturized high performance integrated passives [1]–[4] for the latest IT devices, including CMOS compatible RF integrated inductors and transformers, transmission line devices, electromagnetic noise countermeasure [5], sensors [6],[7], etc.

Nanostructured $\text{Ni}_x\text{Zn}_{1-x}$ Fe2O4 ( $x$ = 1, 0.5) films, about 1.5 µm thick on Si (100) substrates, were deposited using a low-temperature ( $A_{1g}$ vibration mode in Raman spectra of both films reveals a ‘‘far-from-equilibrium’’ crystallographic inversion induced by the MAS process. Its effect on the magnetic characteristics of the films is analyzed here. Both films exhibit in-plane ( $xy$ plane) isotropy with very low room-temperature coercivities, 25 Oe for NF and 35 Oe for ZNF, which is essential for high-frequency, soft magnetic applications. The presence of interparticular dipolar interaction in both films is confirmed from temperature-dependent magnetization measurements made under different dc bias fields. The CMOS-compatible ferrite processing and superparamagnetic Ni-ferrite and NiZn-ferrite thin films presented here can meet upcoming technological needs in on-chip integrated passive devices.

Fe-Co-Ni magnetic thin films with continuously varying compositions have been fabricated by the magnetron co-sputtering method. The films were characterized by high-throughput techniques. The results reveal the correlation between a range of compositions and the electrical properties of the films fabricated at various process parameters.Introduction: Soft magnetic materials are essential elements of electro-magnetic energy transformation technologies and they are widely used in various distribution, conversion, generation devices, such as transformers, motors, converters, generators, actuators, sensors etc. However, it usually takes long time for a new material before its acceptance for commercial application. Therefore, it is very crucial to speed up the discovery of new materials and incorporate them into various systems. High-throughput methods are efficient research methods [1-3] to explore this immense search space to identify new or optimized materials. Fe-Co based alloys received great attention due to high saturation magnetization. And what makes them even more fascinating is that their magnetic and electric properties can be tuned by controlling the alloy composition and microstructure. Among these compositions, Fe-Co-Ni films revealed significant induced magnetic anisotropy, low coercivity and high anisotropy of magnetoresistivity, what makes them a good candidate for technical applications. The resistivity is an important parameter to determine power loss in many soft magnetic applications. In this work we studied the effect of process parameters on the structure and resistivity of compositionally graded Fe-Co-Ni films to find process conditions at which optimum properties are obtained.Experimental details: Fe-Co-Ni films with continuously varying alloy compositions were fabricated by the magnetron sputtering method. Two experimental procedures were designed: a) Fe-Co-Ni films were deposited on SiO2/Si substrates by co-sputtering of permalloy and Co target materials using DC sources at different substrate temperatures (Ts): in particular, ambient temperature, 300 °C and 500 °C; b) the film was deposited at ambient temperature and annealed for 2 hours in vacuum at 500 °C. The base pressure in the chamber was controlled at 4 x 10 - 4 Pa. Depositions were performed in argon gas environment while the pressure was kept approximately at 0.3 Pa. For compositional, structural and electrical properties high-throughput Electron Probe Micro-Analysis (EPMA), X-ray Diffraction, four-point probe measurements were performed to determine chemical compositions, structure and resistivities of the films. Results and discussion: Fe-Co-Ni films with continuously varying alloy compositions were fabricated by magnetron sputtering method. The results of high-throughput Electron Probe Micro-Analysis measurements across Fe-Co-Ni films (Fig.1) revealed that atomic composition of Ni was highest, while Co was lowest in the film fabricated at Ts = 300 °C. The ratios of Co and Ni atomic compositions in deposited graded films were calculated as well. We found that Fe-Co-Ni film fabricated at Ts = 300 °C shows the lowest ratio as compared to other films. XRD measurements and analysis of multiple selected areas on Fe-Co-Ni film fabricated at ambient substrate temperature exhibited amorphous structure. As the substrate temperature increased diffraction peaks appeared, showing a clear change in structure. The diffraction patterns showed that only one FCC phase appeared. The peak intensity increased with temperature and the grain sizes became larger. The increase of peak intensity and average grain size indicated that increasing the substrate temperature from room temperature to 500 °C enhances the crystallinity of Fe-Co-Ni films. As for the annealed samples the intensity of the peak was low, and peak shifted towards lower angles indicating crystal lattice expansion. In addition, oxide peaks have been observed. Fig. 2 shows the measured resistivities as a function of composition of various process parameters. Resistivities of the graded film deposited at Ts =300 °C exhibited higher values than resistivities of the films deposited at ambient, 500 °C, and at ambient temperature followed by annealing at 500 °C. These results indicate that Ni plays important role in tuning resistivities of the films.Conclusion: Fe-Co-Ni films with continuously varying compositions have been fabricated by magnetron sputtering and characterized by high-throughput experimentation methods. The results revealed the correlation between continuously varying alloy compositions and selected properties of the films fabricated at various process parameters. Acknowledgement: This work is supported by the AME Programmatic Fund by the Agency for Science, Technology and Research, Singapore under Grant No. A1898b0043 **

Nanocomposite materials consisting of small crystalline grains embedded within an amorphous matrix show promise for many soft magnetic applications. The influence of pressure is investigated by in situ diffraction of hammer milled Fe89Zr7B4 during heating through the α → γ Fe transition at 0.5, 2.2, and 4.9 GPa. The changes in primary and secondary crystallization onset are described by diffusion and the energy to form a critical nucleus within the framework of classical nucleation theory.

Physical properties of La3+ ion doped Ni[sbnd]Zn based spinel ferrite nanomaterials for technological applications

Magnetic properties of M-type Sr hexaferrite/Fe bilayers

Nanocrystalline (nc) Ni films show pronounced grain growth and suffer from concomitant deterioration of their mechanical and magnetic properties after annealing at relatively low temperatures (T(ANN) ≥ 475 K). This constitutes a drawback for their applicability as coatings or in components of miniaturized devices. This work reveals that the thermal stability of nc Ni is significantly improved by controllably alloying Ni with Cu, by means of electrodeposition, to form a Ni(1-x)Cu(x) solid solution. To tune the composition of such nc alloys, Ni(1-x)Cu(x) films are deposited galvanostatically using an electrolytic bath containing Ni and Cu sulfate salts as electroactive species, saccharine as grain-refining agent, and applying current densities ranging from -10 to -40 mA cm(-2). The enhanced thermal stability is ascribed to segregation of a Cu-rich phase at the Ni(1-x)Cu(x) grain boundaries, which acts as a shielding layer against grain growth. As a result, high values of hardness (in excess of 6 GPa) remain in nc Ni(1-x)Cu(x) for x ≥ 0.3, even after annealing at T(ANN) ≥ 575 K. From a magnetic point of view, Ni(1-x)Cu(x) films possess lower coercivity values than pure nc Ni films, both in the as-prepared and annealed states, thus offering potential advantages for certain soft magnetic applications.

Amorphization of cobalt-rich magnetic alloys by high energy ball milling

Controlling electromagnetic and mechanical behaviors of geopolymer matrix with nano-SiO2@Fe3O4 magnetofluid for soft magnetic applications

Fe-Ga-Tb alloys for soft magnetic applications

La principal desventaja de las aleaciones con memoria de forma ferromagnéticas obtenidas por fundición es su fragilidad. Para superar esta desventaja la metalurgia de polvos es una técnica ideal para la consolidación de las piezas, por lo que este trabajo se orientó a estudiar el efecto generado por los procesos de molienda y sinterizado de polvos sobre la evolución de las fases cristalinas que le confieren la memoria de forma a estos materiales. Para ello se prepararon polvos de la aleación ferromagnética con memoria de forma Ni53.5-Fe19.5-Ga27 a partir de un lingote fundido mediante molienda mecánica, durante dos tiempos diferentes de molienda de 30 y 60 minutos. La evolución de las fases fue estudiada mediante difracción de rayos X (DRX) a alta temperatura (HTXRD), mientras que el sinterizado fue evaluado por medio de ensayos de dilatometría. Los estudios de DRX mostraron que se pueden presentar cuatro fases diferentes en función del tamaño de partícula y de la temperatura de tratamiento térmico. Los polvos de tamaños más gruesos presentaron una estructura B2 acompañados de la fase γ mientras que los más finos presentaban una estructura L21, cuando se trataron por debajo de 1173 K. Por otro lado, los polvos más finos tenían una estructura martensítica modulada M14 después del sinterizado a una temperatura superior a 1273 K. El sinterizado de los polvos fue lento y no indicó claramente un mecanismo de difusión de masa predominante.