Microstructure and Magnetic Properties of Nanocrystalline Fe 93-x-y Z r7 B ,x Cu y Alloys
- PDF / 388,792 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 35 Downloads / 233 Views
ABSTRACT An unconventional technique combining Mossbauer spectroscopy with the effects induced by magnetic radio-frequency fields (if collapse and if sidebands) is employed to study the microstructure and magnetic properties of nanocrystalline clusters of bcc Fe formed by annealing amorphous Fe93-xyZr7BxCu (x=6, 8, 12, y=0, 2) alloys at 500-6000 C. The rf-M6ssbauer experiments allow us to distinguish magnetically soft nanoclusters from magnetically harder microcrystalline phases. The dependence of the bcc Fe phase formation on the alloy composition is discussed. The M6ssbauer results are supplemented by DSC measurements.
INTRODUCTION Recently, a new class of soft magnetic materials with high saturation magnetization and low magnetostriction has been developed by utilizing the first stage of crystallization of amorphous Fe-based alloys. It was found that by annealing the amorphous FeSiB-based alloys containing Cu and Nb the nanocrystalline bcc Fe(Si) phase is formed which exhibits excellent soft magnetic properties [1]. Addition of Cu decreases the crystallization temperature and increases the nucleation rate, and a small amount of Nb limits the grain growth. The good soft magnetic properties of nanocrystalline alloys are well explained by the reduction of the effective magnetic anisotropy due to refinement of the grain size [2]. A nanocrystalline bcc Fe phase was obtained in ternary FeZrB alloys which reveal superior magnetic properties (higher saturation magnetization and permeability) as compared with FeCuNbSiB alloys [3]. Annealing of the amorphous precursor causes formation of nanoscale grains of bcc Fe which exhibit high saturation magnetization combined with low anisotropy and coercive fields and vanishing magnetostriction. Addition of 1-2% Cu to FeZrB alloys decreases the crystallization temperature and increases the nucleation rate. Boron enhances thermal stability of the nanocrystalline bcc phase [4] and affects the homogeneity of the bcc precipitates [5]. The structure and magnetic properties of nanocrystalline alloys have been extensively investigated by various experimental techniques including the Mossbauer spectroscopy which was successfully used for phase identification. However, information regarding the grain size and magnetic anisotropy is not available by conventional Mossbauer measurements. Therefore in the study of the microstructure and magnetic properties of the FeZrBCu alloys we applied an unconventional technique which combines the Mossbauer effect with the phenomena induced by an external radio-frequency field (if collapse and sideband effects) [6]. The collapse of the magnetic hyperfine splitting occurs due to fast magnetization reversal induced by an external radio-frequency (rf) magnetic field. If the frequency of the if field is larger than the Larmor precession frequency and the if field is strong enough to overcome local magnetic anisotropy, then the magnetic hyperfine field is averaged to zero at the Mossbauer nuclei. The if-collapsed spectra consist of a single line or a quadrupol
Data Loading...
