Aluminum Nano-polycrystalline Substance with Ferromagnetics and Application to High-Frequency Core Inductor

It has showed in experiments that aluminum nano-polycrystalline substances are ferromagnetic. A magnetic hysteresis curve measured by SQUID suggested the ferromagnetism. Al bulk is normally thought to be non-magnetic body. Authors also fabricated core inductors using Al nano-polycrystalline substances and measured the inductances of cored inductors with frequency dependence. Al nano-polycrystalline substance was fabricated by sintering Al nanopaste with Al nanoparticles. Al nanoparticles were prepared by using laser ablation in liquid. The structures and components of the sintered Al nano-polycrystalline substances were analyzed by SEM and EDX. It has been shown that inductor using Al nano-polycrystalline substance with low volume resistivity, which is the same order of metal, works at low frequencies below 500 Hz, while inductor using substance with high volume resistivity works at high frequency of 5 MHz. Our analysis of Al nano-polycrystalline substance with high volume resistivity revealed relative permittivity of 7 at frequency of 1 MHz. It has been expected that these inductors to work at frequency of a few GHz because the magnetic resonance frequency of the Al nano-polycrystalline substances were evaluated to be 5.6 GHz and the high volume resistivity results in suppressing the eddy currents.