P. Deppe

A NMR and Mössbauer study of Nd2Fe14B

Mossbauer spectroscopy and spin echos nuclear magnetic resonance were used in order to study the hyperfine fields (HF) at the six Fe sites and the B site in Nd2Fe14B. At 4.2 K hyperfine fields and Fe magnetic moments for the different sites in the range 307–372 kOe and respectively 2.05–2.48 μB have been found. The transferred HF of 31.25 kOe at the B site has a strong local character, being determined by the six next‐nearest Fe atoms in the corner of the trigonal prism in which B atoms are located.

Susceptibility and Mössbauer studies of magnetic rare earth-iron-silicides

Abstract Ternary rare earth-iron-silicides of the Sc 2 Fe 3 Si 5 structure type have been studied by means of susceptibility measurements between 1.2 and 300 K and the Mossbauer effect at 4.2 K and room temperature. The compounds RE 2 Fe 3 Si 5 with RE = Gd—Er are antiferromagnetic with Neel temperatures below 11 K. Above 60 K, the susceptibilities follow a Curie- Weiss law with effective magnetic moments per RE atom approximately equal to the free ion values. 57 Fe Mossbauer effect measurements of the above series and the superconductors forming with Sc, Y and Lu show quadrupole split spectra with small positive values of the isomer shift, indicating the absence of any magnetic moment at the iron site. There is no significant paramagnetic contribution to the 57 Fe hyperfine field below the Neel temperature in the case of the antiferromagnetic compounds in applied fields up to 50 kG.

A 57Fe Mössbauer study of Nd2(Fe1−xCox)14B

A Mossbauer study of the compositional series Nd2(Fe1−xCox)14B confirmed the preferential occupation of j2 sites by the Fe atoms at least for x>0.6 and the strong dependence on x of the relative amount of Fe distributed on this type of site. The j2‐site preference of Fe also influences the hyperfine field of Fe at the j2 site as a consequence of the higher concentration of Co around the j2 sites as compared to that of a statistical distribution.

Hyperfine interactions and magnetization of (Fe1−xCox)80B20 amorphous alloys

Mossbauer spectra of ternary (Fe1−xCox)80B20 ferromagnetic amorphous alloys were taken at 300, 77, and 6 K. The relatively broad distributions of the Fe57 hyperfine field could be fitted to quasi‐symmetrical Gauss profiles with a relative half‐intensity line width of 8–10%. Whereas the average hyperfine field HF at 6 K decreases slowly with x for x≳0.1, the isomer shift increases with x stronger than in the case of (Fe1−xNix)80B20 amorphous alloys. The saturation magnetization Ms has been measured in the temperature range 4–300 K. A linear dependence of HF (at 6 K) on the average magnetic moment μ holds over the whole investigated compositional range according to the equation HF = aμFe+μb where μFe is the moment of Fe in Fe80B20, a≃134 kOe/μB and b≃10 kOe/μB. A small enhancement of HF takes place only in the range 0<x<0.2 as does the average magnetic moment, but for both HF and μ the changes are much smaller than the crystalline FeCo alloys. The dependence of Ms on T is in very good agreement with the Blo...

Magnetic and M&#246;ssbauer investigation of amorphous (Fe x Ni 1-x ) 80 B 20 alloys

A Mossbauer and magnetic study of the amorphous systems (Fe x Ni 1-x ) 80 B 20 and (Fe x Ni 1-x ) 80 B 19 Si 1 in the temperature range 4.2 - 300 K has been undertaken. Besides the average hyperfine fields at the iron sites, in three cases61Ni average hyperfine fields have also been determined. It is concluded that at high Ni concentrations the atomic magnetic moments for both Fe and Ni decrease, the latter decreasing stronger and collapsing close to Ni 80 B 20 . The ratio D/T c , with D the spin wave stiffness constant obtained from the coefficient B of the Bloch law which describes satisfactorily the low temperature dependence of the saturation magnetization and hyperfine fields, has a rather pronounced discontinuity between 30 and 40 at% Ni, possibly due to some changes in the short range order.

A Mössbauer study of Al and Ga substituted magnetite

A Mossbauer study of Fe3−xAlxO4 and Fe3−xGaxO4 has been undertaken. Measurements at low temperatures in magnetic fields enabled us to better separate the Fe(A) and Fe(B) subspectra and to determine the cation distribution on tetrahedral and octahedral sites. Whereas Al up to x=1.4 shows a strong preference for B sites, giving rise to a normalization of the spinel structure with Fe2+ located mainly in tetrahedral sites, Ga distributes over both A and B places without tendency towards normalization at least below x≲1.2.

A neutron and Mössbauer study of TlFexS2 compounds

Abstract Structural and magnetic properties of monoclinic TlFeS 2 and tetragonal TlFe x S 2 (1.3⩽ x ⩽1.8) are reported. All compositions are antiferromagnetic. In tetragonal TlFe x S 2 three inequivalent iron moments are identified reflecting the surrounding Fe vacancy arrangement.

Hyperfine fields and magnetic moments of RE2Fe14B

Abstract Mossbauer spectroscopy and spin echo NMR were used in order to determine transferred hyperfine fields at B and Gd sites and the hyperfine fields and magnetic moments of the 6 crystallographically different Fe atoms in the structure of RE 2 Fe 14 B with RE = La, Ce, Gd.

Mössbauer spectroscopy of R2Fe14B and related compounds

The Mössbauer Spectroscopy (MBS) has been widely used in the last 4 years for the study of the recently discovered ternary compounds R2Fe14B where R means Y, Th or a rare earth element. The strong interest for this class of intermetallics arose drastically after the discovery of the exceptional properties of Nd2Fe14 as an ideal material for permanent magnet applications.The newest results about hyperfine fields BHF, quadrupole splitting EQ and isomer shifts I.S. at the 6 crystallographically different Fe sites and at the 2 R sites in the R2Fe14B and their impact on the understanding of the local magnetic moments and magnetocrystalline anisotropy will be reviewed.In the case of RFe12−xMx compounds where M=V, Ti, Si, Mo, W, Cr, complex Mössbauer spectra were obtained because of the presence of 3 crystallographically inequivalent Fe sites and the presence of differents amounts of the M component on one or more of these sites.

A mössbauer spectroscopy study of R2Fe14B1 − xCx

Abstract When boron is replaced with carbon in R2Fe14B, the iron hyperfine fields are reduced by as much as 7% at room temperature because of a lowering of the iron moments. This reduction results mainly from an increased electron transfer into the iron minority spin band by substituting carbon for boron. In the samples investigated, about 25% of the iron is present in phases other than R2Fe14X (X ≡ B or C).