Perpendicular magnetic anisotropy in amorphous ferromagnetic CoSiB/Pt multilayers

Influence of a Reduction Process on the Phase Component and Magnetic Properties of NdFeB Magnetic Nanoparticles

NdFeB magnetic nanoparticles with a main phase of Nd₂Fe₁₄B have successfully been synthesized. The preparation includes the following processes. First, the NdFeB intermediate was synthesized by a wet-chemical method. The NdFeB intermediate was annealed at 800 °C, which resulted in the formation of an NdFeB oxide. Then, the NdFeB oxide was reduced into NdFeB nanoparticles by a second-step reduction annealing with a CaH₂ reductant. The second-step reduction annealing temperature was a key factor in preparing the NdFeB nanoparticles. A lower reduction temperature of 900 °C could not completely reduce the NdFeB oxide into Nd₂Fe₁₄B. There were some residual unreduced nonmagnetic phases in the prepared materials, which resulted in obvious decreases of coercivity. A sufficiently high second-stage reduction temperature resulted in an increased reduction, and more of the Nd₂Fe₁₄B phase could be obtained. In this work, nanoparticles with a uniform morphology and an increased Nd₂Fe₁₄B phase could be obtained at an optimum reduction temperature of 940 °C, achieving a high coercivity of 5.4 kOe.

Electrical and Optical Properties of Co75Si15B10 Metallic Glass Nanometric Thin Films

Co-based (Co₇₅Si₁₅B₁₀) thin-film metallic glass (TFMG) with nanometric thicknesses (100~300 nm) was investigated for its structural, electrical, and optical properties. The TFMG structure was examined using scanning electron microscopy and X-ray diffraction, while electrical properties were examined using inductance/capacitance/resistance spectroscopy, cyclic voltammetry, and Hall effect measurements. In addition, optical absorption/reflection/transmittance measurements were performed to examine optical properties. Results revealed that Co-based TFMGs, which have an amorphous structure without surface defects, behave like a dielectric material, with higher resistivity and much lower carrier concentration than pure cobalt (Co) thin films of the same thickness, despite its mobility being modestly larger than its Co counterparts. Meanwhile, the optical investigation of TFMG enabled us to determine the complex relative permittivity (complex relative dielectric constant) ϵr˜ at a visible wavelength (632.8 nm). Moreover, unlike normal metals, TFMGs exhibited a large positive value of the real part of ϵr˜, while exhibiting properties of substantial absorption of light (absorption coefficient α). It was also found that the Co-based TFMG gained optical transparency for thicknesses less than 5 nm. TFMGs demonstrated the nearly thickness-independent properties of the electrical and optical parameters probed, a feature of high-index, dielectric-like material with negligible size effects, which may have applications in micrometer-scaled optoelectronic and magneto-optical devices.