The Technical Committee of the IEEE Magnetics Society has selected 7 research topics to develop their roadmaps, where major developments should be listed alongside expected timelines; (i) hard disk drives, (ii) magnetic random access memories, (iii) domain-wall devices, (iv) permanent magnets, (v) sensors and actuators, (vi) magnetic materials and (vii) organic devices. Among them, magnetic materials for spintronic devices have been surveyed as the first exercise. In this roadmap exercise, we have targeted magnetic tunnel and spin-valve junctions as spintronic devices. These can be used for example as a cell for a magnetic random access memory and spin-torque oscillator in their vertical form as well as a spin transistor and a spin Hall device in their lateral form. In these devices, the critical role of magnetic materials is to inject spin-polarised electrons efficiently into a non-magnet. We have accordingly identified 2 key properties to be achieved by developing new magnetic materials for future spintronic devices: (1) Half-metallicity at room temperature (RT); (2) Perpendicular anisotropy in nano-scale devices at RT. For the first property, 5 major magnetic materials are selected for their evaluation for future magnetic/spintronic device applications: Heusler alloys, ferrites, rutiles, perovskites and dilute magnetic semiconductors. These alloys have been reported or predicted to be half-metallic ferromagnets at RT. They possess a bandgap at the Fermi level EF only for its minority spins, achieving 100% spin polarisation at EF. We have also evaluated L10-alloys and D022-Mn-alloys for the development of a perpendicularly anisotropic ferromagnet with large spin polarisation. We have listed several key milestones for each material on their functionality improvements, property achievements, device implementations and interdisciplinary applications within 35 years time scale.Comment: Open Access, 11 pages, 11 figures, advance online publication IEEE Transactions on Magnetic
Nickel zinc ferrite nanoparticles (Ni 0.20 Zn 0.44 Fe 2.36 O 4) have been produced at room temperature, without calcination, using a reverse micelle process. Particle size is approximately 7 nm as determined by x-ray powder diffraction and transmission electron microscopy. Saturation magnetization values are lower than anticipated, but are explained by elemental analysis, particle size, and cation occupancy within the spinel lattice. Extended x-ray absorption fine structure analysis suggests that a significant amount of Zn 2ϩ , which normally occupies tetrahedral sites, actually resides in octahedral coordination in a zinc-enriched outer layer of the particles. This ''excess'' of diamagnetic Zn can thus contribute to the overall decrease in magnetism. Further, this model can also be used to suggest a formation mechanism in which Zn 2ϩ is incorporated at a later stage in the particle growth process.
Core-shell structured polystyrene-gold composite particles are synthesized from one-step Pickering emulsion polymerization. The surface coverage of the core-shell composite particles is improved with increasing gold nanoparticle (AuNP) hydrophobicity and concentration. At high surface coverage, the AuNPs exhibit an ordered hexagonal pattern, likely due to electrostatic repulsion during the emulsion polymerization process. In addition to core-shell structured polystyrene-gold composite particles, an intriguing observation is that at low AuNP concentrations, asymmetric polystyrene-gold nanocomposite particles are simultaneously formed, where a single gold nanoparticle is attached onto each polystyrene particle. It is found that these asymmetric particles are formed via a "seeded-growth" mechanism. The core-shell and asymmetric polystyrene-gold composite particles prove to be efficient catalysts as they successfully catalyze the Rhodamine B reduction reaction with stable performance and show high recyclability as catalysts.
Plasma synthesis has previously been shown to be a viable route to producing nanocrystalline magnetite and Ni ferrite nanoparticles. In this work nanocrystalline powders of Mn and Mn–Zn ferrites have been synthesized using a 50 kW–3 MHz rf (radio frequency) induction plasma torch. We investigate these materials for soft magnetic applications. High-energy ball milled Mn + Fe powders and (Mn+Zn) +Fe powders (<10 μm) in the stoichiometric ratio of 1:2 were used as precursors for the ferrite synthesis. Compressed air was used in the oxygen source for oxidation of metal species in the plasma. X-ray diffraction patterns for the plasma-torched Mn ferrite and MnZn ferrite powders were indexed to the spinel ferrite crystal structure. An average grain size of ∼20 nm was determined from Scherrer analysis confirmed by transmission electron microscopy studies. The particles also exhibited faceted polygonal growth forms with the associated truncated cuboctahedral shapes. Room-temperature vibrating sample magnetometer measurements of the hysteretic response revealed saturation magnetization Ms and coercivity Hc of Mn ferrite are 23.65 emu/g and 20 Oe, respectively. The Néel temperatures of Mn ferrite powders before and after annealing (500 °C, 30 min) were determined to be 200 and 360 °C, respectively. Inductively coupled plasma chemical analysis and energy dispersive x-ray analysis data on the plasma-torched powders indicated deviations in the Mn or Zn contents than the ideal stoichiometry. MnZn ferrite was observed to have a Néel temperature increased by almost 400 °C as compared with as-synthesized Mn ferrite but with a larger coercivity of ∼35 Oe.
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