Zuxiong Xu

Structural defects and internal stress field distribution in nanocrystalline Fe73.5Cu1Nb3Si13.5B9

Abstract The positron annihilation Doppler broadening technique and micromagnetism method have been employed to investigate structural defects in nanocrystalline Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 alloy. The results show that the precipitation of α-Fe(Si) in the amorphous matrix involves few defects at the early stage of crystallization, while at the second stage a large amount of defects associated with grain boundaries becomes dominant. The pinning centers resulting from quasi-dislocation dipoles have an intense influence on the soft magnetic properties. In view of these structural defects, the optimum soft magnetic properties of nanocrystalline Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 can be explained.

The amorphous-to-nanocrystalline transformation in Fe73.5Cu1Nb3Si13.5B9 studied by thermogravimetry analysis

Abstract The magnetic properties and isothermal crystallization process of amorphous Fe 73.5 Cu 1 Nb 3 Si 13.5 B 9 alloy have been investigated by means of the thermogravimetry analysis method (TGA) and X-ray diffraction measurements. The TGA curves for samples annealed at various temperatures indicate three distinct regions corresponding to the different magnetic characteristics of the as-quenched, the nanocrystalline and the polycrystalline structures. The results of a kinetic analysis show that Cu element plays an important role in the nucleation of ultrafine grains. The formation of Cu-rich regions reduces the activation energy for the nucleation of α-Fe(Si), so that the α-Fe(Si) phase can nucleate and precipitate preferentially in the Cu-rich regions. A comparison with isothermal DSC analysis shows that more information about nucleation at the early stage of crystallization can be obtained by the TGA method.

Interfacial structure of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 studied by positron annihilation

Nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloy prepared by the crystallization of amorphous alloy has been studied by using the positron annihilation technique. Positron parameters, i.e., lifetime τ1, τ2, and line shape parameter S are obtained as a function of the annealing temperature. The results show that there exist two types of defects at the interfaces of nanocrystalline Fe73.5Cu1Nb3Si13.5B9 alloy: vacancy‐like and vacancy‐like group microvoids characterized by the lifetime τ1 and τ2. The former is in overwhelming majority. The changes of the structural defects corresponding to different stages, structural relaxation, and crystallization are discussed.

The interfacial structure of nanocrystalline Fe73.5Cu1Mo13Si13.5B9 studied by Mössbauer spectroscopy

Abstract Nanocrystalline Fe73.5Cu1Mo3Si13.5B9 prepared by crystallization of the amorphous alloy was investigated by using Mossbauer spectroscopy and X-ray diffractometry. The present study focuses on the interfacial composition and the important role of the interfacial component in the development of the nanocrystalline structure. On the basis of a newly developed fitting program, the amorphous phase is denoted by a low field component and a high field one. Upon crystallization, the former, which corresponds to the boundary regions adjacent to the grains become more significant. The different stages associated with the crystallization are discussed.

MOSSBAUER STUDIES OF MAGNETIC TEXTURE IN NANOCRYSTALLINE FE73.5CU1NB3SI13.5B9 ALLOY

Mössbauer measurements have been carried out using non-polarized absorbers in order to investigate the magnetic texture in nanocrystalline Fe73.5Cu1Nb3S13.5B9 prepared from the amorphous state by crystallization. The results indicate a significant variation of magnetic domains in ribbons with the annealing temperature. Upon crystallization the component of the magnetization vector oriented parallel to the long axis of ribbons increases significantly and becomes dominant. The non-field annealing-induced magnetic texture probably arises from the shape anisotropy and intensely influences the initial magnetization process.

Compositional evolution and magnetic properties of nanocrystalline Fe81.5Cu0.5Mo0.5P12C3Si2.5

The amorphous alloy Fe81.5P12C3Cu0.5Mo0.5Si2.5 has been prepared and the crystallized alloy exhibits an ultrafine structure with a grain size of about 20 nm and excellent soft magnetic properties. The coercivity and the core loss as low as 6.7 A/m, 0.26 W/kg, respectively, and the maximum permeability as high as 10.2×104 at an optimal annealing temperature of about 360 °C were obtained. By means of x‐ray diffraction, transmission electron microscope, and Mossbauer spectroscopy measurements, microstructures of the alloy were investigated as a function of the annealing temperature. The primary crystallization produces ultrafine grains of α‐Fe(Si) solid solution with a grain size of about 20 nm precipitated in the residual amorphous matrix. The Si in the α phase was estimated near to be completely disorder ranged and the Si concentration was determined to be about 2%–5%. The Fe3P phase appears in the residual amorphous phase upon annealing at 420 °C.

Neutron diffraction and Mössbauer effect study of the structure of DySixFe11−xCoN alloys

DySixFe11−xCo (x=0.5, 1.0, and 1.5) alloys and their nitrides are studied by x‐ray diffraction, Mossbauer effect and neutron diffraction experiments. The results show that both Si and Co atoms can occupy the 8f and 8j sites, and more preferentially occupy the 8f sites. Nitrogen atoms as interstitial atoms enter into the 2b site. The nitrides have high Curie temperatures. The results of Mossbauer spectroscopy indicate that nitriding increases the hyperfine fields of all Fe sites.

Structure and magnetic properties of nanocrystalline ferromagnets (I): Effective anisotropy

The role of effective anisotropy in nanocrystalline ferromagnets is investigated. These alloys are prepared by annealing amorphous ribbons and have excellent soft magnetic properties. A two-phase model is established considering the role of the intergranular amorphous phase. The results indicate a strong dependence of effective anisotropy on the structure and magnetic parameters of the amorphous phase as well as on the size of a grains. In view of the new model, the magnetic hardening beyond the optimally annealing temperature seems to be ascribed to the deterioration in magnetic properties of interfacial amorphous phase.

Studies of Mössbauer spectrum on Sm2(Fe,Ga)17C1.5 alloy

X‐ray‐diffraction patterns and Mossbauer spectra of Sm2(Fe,Ga)17C1.5 alloys have been studied. The results of x‐ray‐diffraction patterns and Mossbauer spectra indicate that little α‐Fe and carbonides appear in Sm2(Fe,Ga)17C1.5 alloys. The addition of a few Ga atoms show that the thermal stability in Sm2(Fe,Ga)17C1.5 alloys is getting better. Structural analyses indicate C atoms as interstitial atoms occupying the 9d site. Ga atoms seem to substitute partially for Fe atoms and occupy preferentially the 18h site.

Neutron‐diffraction study on the structure of Nd(TiFe)12Nx and Nd(TiFeCo)12Nx alloys

The preference of nitrogen atoms in Nd(FeTi)12Nx and Nd(FeTiCo)12Ny alloys have been studied by neutron diffraction. The results show that Ti atoms are preferentially to occupy the 8i sites, but Co atoms enter the 8f rather than the 8i site. Nitrogen atoms occupy the 2b sites in Nd(FeTi)12Nx and Nd(FeTiCo)12Ny.