| Nanocrystalline composite soft magnetic materials, which consist of nanoscale crystalline ferromagnetic phases (typical 10 nm) homogeneously dispersed in an amorphous matrix are derived from crystallizing amorphous ribbons. The excellent soft magnetic properties, such as extremely low coercivities, high permeabilities, low energy losses, etc, have attracted the major interest and research activity in both academic community and industrial community in the past two decades. In this thesis, two classes of nanocrystalline composite soft magnetic alloys are developed from their amorphous precursors, accompanying the analysis on their sturctural evolution, thermal kinetics and variou magnetic properties.;FeCoB based nanocrystalline composite soft magnetic alloy is developed, in collaboration with Magnetics Division at Spang & Company, for application in high frequency and high temperature. This class of nanocrystalline composite alloy has the nominal composition (FeCo)80Nb4[BGe(Si)] 15Cu1. The crystallization products are bcc FeCo for primary crystallization at 410°C and (FeCoNb)23B 6 for second crystallization. The average grain size is below 10 nm after annealed at 500°C for 1 hour. After transverse field annealing at its primary crystallization temperature, the core loss significantly decreased to the value which can comparable with other commercial soft magnetic alloy.;Another class of nanocrystalline composite soft magnetic alloy is Fe based and Boron free alloy. This class of soft magnetic alloy with the nominal composition Fe79ZrxSi20- xCu1 was developed for low cost on raw materials. The nanocrystalline phase alpha-Fe(Si) with average grain size 10 nm was observed in this kind alloy annealed at 460°C for 1 hour. Cu acts as the nucleation agent for making the precipitated nanocrystals uniform and very fine. The measurement of core loss shows the alloy annealed at 460°C for 2 hour has the relatively core loss which can be comparable that of other commericial nanocrystalline soft magnetic alloy.;Moreover, the analysis on hysteresis behavior and magnetic domain under different annealing conditions are discussed. The Preisach Distribution evaluated by first order reverse curves (FORCs) indicates the reversible process is dominant when the grain size at the sample is close to 10 nm. The irreversible part should be ascribed to the pinning sites by the grain boundaries which is significant when the large grains exist in the sample. |
