Scripta Metallurgica et Materialia最新文献

Systems of small magnetic particles embedded in a nonmagnetic matrix were prepared by high energy ball milling. Besides carefully chosen milling conditions, in situ chemical reactions were used to control the properties of the product.

Nanocomposites of iron particles in metal oxides (Al₂O₃ and ZnO), and magnetite particles in copper metal were prepared by reaction milling. The samples were characterized by X-ray diffraction and magnetic methods. A few hours of ball milling resulted in the completion of most chemical changes. Iron nanoparticles were formed with lattice strains of about 0.005; coercivities up to 400 Oe were achieved. The magnetization of the iron particles is 25–40% less than that expected for bulk iron.

Extrinsic magnetic properties play a major role in determining the performance of magnetic thin films used as magnetic recording media. These extrinsic properties are the ones which are largely determined by the microstructure of the thin magnetic films. In this paper we discuss various ways that the crystallographic texture of thin films can be controlled. We begin with a discussion of the origin of crystallographic texture of underlayers. Next, the origin of crystallographic texture of magnetic thin films by means of epitaxy with the underlayer is discussed. The control of other microstructural features such as grain size and perfection by means of underlayers and interlayers is briefly introduced. Examples from recent research are included.

In this work morphological, crystallographic and magnetic properties of iron nitride powders prepared by room temperature mechano-chemical processing, were studied by SEM, XRD and VSM methods. Nitridation reaction occurs during ball milling of a stoichiometric mixture of αFe powder and highly reactive complex amine compounds: piperazine, pyrazine and pyrazole in the molar ratio 3:1 (Fe:N). The amount of nitride phase produced, depends on milling time, annealing temperature and on the chemical reactivity of the amine compound with iron. Calculation of crystal lattice parameters show that prepared nitrides are similar to stoichiometric Fe₃N hcp type structure. Lattice expansion was found for hexagonal planes due to increase in nitrogen concentration. Magnetic hysteresis parameters were found to be very sensitive to changes in chemical composition. As the amount of nitrogen increases magnetic remanence and coercivity increase but magnetization and calculated average magnetic moment per Fe atom decrease.

Recent developments in high-frequency magnetic thin films are overviewed. The topics discussed are multi-layered nanocrystalline films and two-phase granular alloy films with high electrical resistivity. First, it is shown that Fe/Fe-Hf-C multilayers are promising high-frequency films with saturation magnetization Bs = 20kG and permeability μ′= 6,000 up to 10~20MHz, which are at the highest levels among these types of magnetic thin films. Second, it is shown that (Fe,Co,Ni)-(Si,B,Zr etc.)-(F,O,N) granular alloy films posses uniquely high electrical resistivity ρ as 10³~10 μΩ-cm together with high Bs of about 10kG, and consequently exhibit remarkable frequency dependence of μ′ and loss μ″ up to 500MHz. These new-types of thin films are possible candidate materials for future high-frequency devices such as “magnetic integrated circuits”. The properties are attributed to the two-phase granular structure, consisting of metallic grains and less conductive intergrains.