Non-acicular modified high coercivity iron oxides for high density magnetic recording and the processes of making the same

[[abstract]]The non-acicular modified maghemite and magnetite have high coercivity of, for the maghemite, up to 2200 Oe, saturation and residual magnetization of 63-85 emu/g and 43-52 emu/g, respectively; for the magnetite, the corresponding values are 800-1600 Oe, 82-87 emu/g, and 44-51 emu/g, respectively; while retaining same squareness ratio and same chemistry with conventional iron oxides, fine particle size of around 50 nm, easier dispersion and coating, invaried properties after curing, and low value of temperature coefficient of coercivity (0.24-0.37%/.degree. C. for the maghemite and 0.20-0.33%/.degree. C. for the magnetite), have been invented. They are thus especially suitable for high density recording. The modified maghemite and magnetite are prepared by precipitating from aqueous solution containing Fe, Mn, Co and Zn ions at proper ratio using an organic alkali as precipitant, followed by specific heat treatment sequences.[[fileno]]2020337060007[[department]]材料科學工程學

A Review of the Self-Powered Wiegand Sensor and Its Applications

Self-powered magnetic sensors are fundamental for the development of Industry 4.0, the Internet of things (IoT), wireless sensor networks, unmanned vehicles, smart cities, and sustainability. This review aimed to elucidate the working principles, materials, manufacture, output properties, and perspectives of Wiegand sensors. A Wiegand sensor is composed of a magnetic sensing wire, which is called a Wiegand wire, and a pick-up coil for the output of an electrical signal and energy. The Wiegand sensor requires an external magnetic field of about 70 Gauss to induce Wiegand wire flux changes, which, in turn, generate an output pulse in the pick-up coil. Output energy of more than 3000 nJ per single pulse (open circuit) can be harvested. The output pulse is derived from the large Barkhausen effect. Therefore, the behavior of the sensor output is independent of the triggering and sensing frequencies. The objective of this review article was to comprehensively highlight research endeavors devoted to Wiegand sensors. Furthermore, application scenarios of current research results are highlighted to find potential gaps in the literature and future contributions. Perspectives and research opportunities of Wiegand sensors are proposed

Soft Magnetic Properties of High-Entropy Fe-Co-Ni-Cr-Al-Si Thin Films

Soft magnetic properties of Fe-Co-Ni-Al-Cr-Si thin films were studied. As-deposited Fe-Co-Ni-Al-Cr-Si nano-grained thin films showing no magnetic anisotropy were subjected to field-annealing at different temperatures to induce magnetic anisotropy. Optimized magnetic and electrical properties of Fe-Co-Ni-Al-Cr-Si films annealed at 200 °C are saturation magnetization 9.13 × 105 A/m, coercivity 79.6 A/m, out-of-plane uniaxial anisotropy field 1.59 × 103 A/m, and electrical resistivity 3.75 μΩ·m. Based on these excellent properties, we employed such films to fabricate magnetic thin film inductor. The performance of the high entropy alloy thin film inductors is superior to that of air core inductor

Effects of cathode rotation and substrate materials on electrodeposited CoMnP thick films

In this study, rotating-cathode electrodeposition was performed to deposit 30 μ m thick CoMnP films on various substrate materials at room temperature. The electrodeposition configuration and parameters realized a constant current efficiency of about 95%, which was under activation control rather than mass-transport control. Compositional analysis indicated that the deposited thick films were Co-rich with a Co content 92–95 wt.%, regardless of deposition parameters. X-ray diffraction revealed that cathode rotation physically altered the preferred orientation of Co crystallites. The texture of Co crystallites changed with the cathode rotational speed from distinct hexagonal close-packed (HCP) (002) to a heterogeneous phase mixture of HCP (110) and face-centered cubic (FCC) (220). The substrate materials physicochemically affected the relationship between rotational speed and microstructural evolution. The microstructural texture changed nonlinearly with the cathode rotational speed when the films were deposited on catalytic substrate materials, suggesting a substantial influence of the substrate activation nature. Due to magnetocrystalline anisotropy, the resultant films exhibited hard magnetic properties while depositing at the optimal cathode rotational speed. Stationary-cathode electrodeposition resulted in rough CoMnP films with Co grains of 8–18 nm and high Mn content. These films exhibited unique in-plane magnetic properties compared with the films deposited with electrolyte agitation. This study is the first to investigate the combined effects of cathode rotational speed and the activation nature of substrates on the growth behavior of electrodeposited Co-rich CoMnP thick films. The results can be extended to electrodeposition of other Co-based alloys, such as CoP, CoNiP, CoWP, CoPtP, and CoNiMnP

Anisotropic electrical conduction of vertically-aligned single-walled carbon nanotube films

Anisotropic electrical conduction measurements have been carried out for thin films of vertically-aligned single-walled carbon nanotubes (VA-SWCNTs) grown by an alcohol catalytic CVD process. Combined with controlled synthesis and structure characterization by optical spectroscopy, the influence of the aligned structure on the electrical conduction has been identified. The out-of-plane conductivity of the films was measured to be about 0.56 S/mm, independently of the film thickness. On the other hand, the in-plane conductivity was found to be more than an order of magnitude smaller, which gives rise to highly anisotropic electrical conduction, reflecting the high degree of alignment in the VA-SWCNT films. The in-plane conductivity decreases with increasing film thickness, in contrast to the film of random SWCNT networks, which exhibit thickness-independent in-plane resistance. The thickness-dependent in-plane conductivity can be expounded by a growth model of vertically aligned SWCNT films in which a thin layer of nanotube networks form on top of films at the initial stage of the growth. Such electrical anisotropy of VA-SWCNT films can be useful in miniaturized sensing devices. (C) 2010 Elsevier Ltd. All rights reserved

Formation of Simple Crystal Structures in Cu-Co-Ni-Cr-Al-Fe-Ti-V Alloys with Multiprincipal Metallic Elements

Crystalline solid solutions are typically formed in conventional alloys based on one or two host elements. Here, in this research, four alloys containing multiprincipal metallic elements (≥5 elements) were prepared by casting, splat quenching, and sputtering. Their microstructures and crystal structures were investigated. It was interestingly found that solid solutions with simple fcc or bcc crystal structure were also practically formed in these alloys with multiprincipal elements. All different atoms are regarded as solutes and expected to randomly distribute in the crystal lattices without any matrix element defined