Ji-Jun Sun

57Fe Mossbauer study of metastable 304 stainless steel film with BCC structure

The metastable 304 stainless steel film with BCC structure, fabricated by using a vapour quenching method, is strongly ferromagnetic. The effect of the local environment on the hyperfine parameters, and the influence of the heat treatment and pressure on stability in the metastable phase, were studied by means of conventional and high-pressure 57Fe Mossbauer spectroscopy. Each non-iron nearest-neighbour atom (Cr, Ni and Mn) of Fe atoms decreases the hyperfine field by an average of about 2.3 T and the isomer shift by about 0.01 mm s-1. Moreover, each non-iron next-nearest-neighbour atom is estimated to reduce the hyperfine field by an average of about 1.2 T. It is found that the transformation from the metastable BCC state to the FCC state begins near 500 degrees C and is completed near 800 degrees C. No FCC phase appears under a pressure smaller than 36 kbar. In both cases, however, the magnetization direction of the sample is observed to reorientate, and shows a stronger tendency to the out-of-plane after annealing and under pressures up to 8 kbar, while it is closer to the in-plane under pressures larger than 8 kbar.

57Fe high pressure Mössbauer and X-ray studies of Gd2Fe17C x interstitial compounds

The unit cell volume dependence of the Curie temperature of Gd2Fe17 is studied by means of high-pressure Mössbauer spectroscopy. From the pressure dependence of the average isomer shift of Ge2Fe17 at room temperature, the contribution of the pure magnetovolume effect to the change of the average isomer shift is derived. By combining the Mössbauer measurements of Gd2Fe17Cx with different C concentrations at room temperature, the change ofIS in Gd2Fe17Cx is dominated by the magnetovolume effect. The contribution of the chemical bonding effect is about 24% of that of the magnetovolume effect, but with negative sign.

Preparation and Mössbauer study of Gd2Fe17Cx (x≤2) with higher carbon concentration by melt quenching

Carbides Gd2Fe17Cx with composition up to x=2 were successfully prepared. The single phase Gd2Fe17Cx (x=1.5, 2.0) carbides with higher carbon concentration were first obtained by the melt quenching technique. 57Fe Mossbauer spectra of all compounds were measured and the results show that the average hyperfine field and isomer shift increase with increasing carbon concentration in the studied composition range. The effects of the interstitial carbon atoms on the hyperfine parameters are discussed. According to the result of the quadrupole splitting, the easy magnetization direction at room temperature for all carbides was determined.

Magnetic hyperfine fields in Y2Fe17?x Si x compounds

Y2Fe17−xSix compounds withx=0, 0.5, 1.0, 1.5, 2.0, 2.5 and3.0 were investigated by magnetic measurement andNMR. It is found that with increasing Si content the Curie temperatureTC increases while the average Fe magnetic moment μFe decreases. NMR study indicates that Si preferentially substitute the Fe atoms at 4f sites, which is responsible for the increase ofTC.

Magnetism and hyperfine fields in melt-spun R-Fe-B alloys with a low R concentration (R≡Y, Pr, Nd, Gd or Dy)

The hyperfine fields and magnetic properties of amorphous and crystallized R(x)Nd(4-x)Fe(77.5)B(18.5) (R = Y, Pr, Gd or Dy; 0 less than or equal to x less than or equal to 4) alloys have been investigated by means of magnetization measurements, zero-field spin-echo nuclear magnetic resonance (NMR) and the Mossbauer effect (ME). It is found that the Curie temperatures of amorphous alloys change slightly on the addition of R, but the coercive fields of crystallized alloys decrease monotonically with increasing x for R = Y, Pr and Gd. A small addition of Dy increases the coercivity; full substitution of Nd by Dy leads to low coercivity owing to the formation of the magnetically soft Dy3Fe62B14. NMR, ME and x-ray diffraction indicate that the samples with R = Pr and Gd for 0 less than or equal to x less than or equal to 4 and R = Y and Dy for 0 less than or equal to x less than or equal to 2 consist of Fe3B with a body-centred tetragonal (BCT) structure and a small amount of alpha-Fe. Furthermore, the NMR results indicate that the B-11 hyperfine fields of sn Fe3B increase linearly from 25.3 kOe (34.7 MHz) to 26.3 kOe (36.0 MHz) on the addition of Dy or Gd, but that of alpha-Fe does not change with increasing R concentration; the Mossbauer spectra show that the relative intensity of the subspectrum corresponding to Fe-57 at Fe-III(8g) sites in BCT Fe3B is about 5% weaker than those of the other two, implying that about 5 at.% Fe atoms in this site are substituted by other atoms. According to this, it may be reasonable to assume that R atoms enter into BCT Fe3B.

Mössbauer study of Gd2Fe17C2.0 compound by the melt quenching

Carbide of composition Gd2Fe17Cx compound with higher carbon concentration x = 2 was successfully prepared by the melt quenching. Fe-57 Mossbauer spectra of the carbides (x = 0, 1, 2) were measured at room temperature, the results show that the changing tendency of average hyperfine field and isomer shift is consistent with that of the carbides with x < 1.5. The effects of the interstitial carbon atoms in the Gd2Fe17 compound on the hyperfine parameters were discussed.

Mössbauer study of Y2Fe17N x (x < 3) nitrides

Abstract57Fe Mössbauer spectra of Y2Fe17Nx nitrides were measured. The hyperfine field (Hhf) and the average isomer shift for Y2Fe17 increase obviously after nitrogenation. Forx≥1.1, however, the averageHhf varies only slightly, while the increase ofHhfat each iron site is somewhat different and more pronounced at 4f dumbbell sites than at the other sites when the nitrogen concentration is increased. This means that the influence of the nitrogen atoms on the local magnetic properties of the iron atoms depends sensitively on the configuration of the nearest-neighbor atoms around the iron atoms. The results are compared with the89Y NMR spectra of Y2Fe17Nx.

Nuclear magnetic resonance and Mössbauer effect studies of melt-spun PrxNd4−xFe77.5B18.5 alloys

The effect of Pr substitution on the phase composition and B-11 and Fe-57 hyperfine fields (Hfs) in the samples of Nd4Fe77.5B18.5 has been investigated by means of-zero field spin-echo nuclear magnetic resonance (NMR) and Mossbauer effect(ME). It was found that the phase components had not been influenced by the addition of Pr atoms. The samples annealed at 670 degrees C for about two min. consist of a mixture of body-centered-tetronagonal Fe3B(bct-Fe3B) and alpha-Fe. Furthermore, B-11 NMR peaks of bct-Fe3B broaden to the high-frequency side in the rare earth elements-contained samples compared with pure bct-Fe3B. The substitution of Pr for Nd has not an obvious effect on B-11 hyperfine field.

The effect of Gd substitution on the magnetic properties and hyperfine fields of melt-spun Nd4Fe77.5B18.5 alloys

The hyperfine fields (HFS) and magnetic properties of amorphous and crystallized GdxNd4-xFe77.5B18.5 (0<or=x<or=4) alloys have been investigated by means of magnetization measurements, zero-field spin-echo nuclear magnetic resonance (NMR) and Mossbauer effect (ME). For comparison, the x-ray diffraction (XRD) pattern of Nd4Fe77.5B18.5 annealed at 670 degrees C for a short time is also presented. It is found that the Curie temperatures of amorphous alloys increase slightly on addition of Gd, but the coercive fields of crystallized alloys decrease monotonically with increasing x. NMR, ME and XRD indicate that these samples consist of Fe3B with a body-centred tetragonal structure (BCT Fe3B) and a small amount of alpha -Fe, with no Nd2Fe14B and Nd1.1Fe4B4 phases. Furthermore, the NMR results indicate that the 11B HFS of BCT Fe3B increase linearly from 25.3 kOe (34.7 MHz) for x=0 to 26.3 kOe (36.0 MHz) for x=4, but that of alpha -Fe does not change with increasing Gd concentration; the Mossbauer spectra (MSs) show that the relative intensity of the subspectrum corresponding to 57Fe at FeIII(8g) sites in BCT Fe3B is about 5% weaker than those of the other two, implying that about 5 at.% Fe atoms in this site are substituted by other atoms. According to this, it may be reasonable to assume that the R atoms enter into the BCT Fe3B.

A 57Fe high-pressure Mossbauer study of the ferromagnetic intermetallic compound Gd2Fe17

The effect of pressure up to 5.5 GPa on the magnetic behaviour of Gd2Fe17 has been investigated using the Fe-57 high-pressure Mossbauer effect technique. We show that the decrease of the average magnetic hyperfine field at 300 K can be well explained by the decrease of Curie temperature with pressure, while the Fe local magnetic moment remains almost stable in this pressure range. The decrease of the isomer shift with increasing pressure indicates a corresponding increase of the selectron density at the Fe-57 nucleus, which is mainly caused by the volume compression of the 4s conduction electrons.