Investigation of (Fe,Co)NbB-Based Nanocrystalline Soft Magnetic Alloys by Lorentz Microscopy and Off-Axis Electron Holography.

The relationship between microstructure and magnetic properties of a (Fe,Co)NbB-based nanocrystalline soft magnetic alloy was investigated by analytical transmission electron microscopy (TEM). The microstructures of (Fe0.5Co0.5)80Nb4B13Ge2Cu1 nanocrystalline alloys annealed at different temperatures were characterized by TEM and electron diffraction. The magnetic structures were analyzed by Lorentz microscopy and off-axis electron holography, including quantitative measurement of domain wall width, induction, and in situ magnetic domain imaging. The results indicate that the magnetic domain structure and particularly the dynamical magnetization behavior of the alloys strongly depend on the microstructure of the nanocrystalline alloys. Smaller grain size and random orientation of the fine particles decrease the magneto-crystalline anisotropy and suggests better soft magnetic properties which may be explained by the anisotropy model of Herzer.

Nanoscale-driven crystal growth of hexaferrite heterostructures for magnetoelectric tuning of microwave semiconductor integrated devices.

A nanoscale-driven crystal growth of magnetic hexaferrites was successfully demonstrated at low growth temperatures (25-40% lower than the temperatures required often for crystal growth). This outcome exhibits thermodynamic processes of crystal growth, allowing ease in fabrication of advanced multifunctional materials. Most importantly, the crystal growth technique is considered theoretically and experimentally to be universal and suitable for the growth of a wide range of diverse crystals. In the present experiment, the conical spin structure of Co2Y ferrite crystals was found to give rise to an intrinsic magnetoelectric effect. Our experiment reveals a remarkable increase in the conical phase transition temperature by ∼150 K for Co2Y ferrite, compared to 5-10 K of Zn2Y ferrites recently reported. The high quality Co2Y ferrite crystals, having low microwave loss and magnetoelectricity, were successfully grown on a wide bandgap semiconductor GaN. The demonstration of the nanostructure materials-based "system on a wafer" architecture is a critical milestone to next generation microwave integrated systems. It is also practical that future microwave integrated systems and their magnetic performances could be tuned by an electric field because of the magnetoelectricity of hexaferrites.