Mossbauer spectroscopy magnetic hyperfine field

Some uranium magnetic compounds were measured by Mossbauer spectroscopy. The hyperfine fields in these compounds were determined by Mossbauer spectroscopy [6,7,9,11]. In most of the uranium compounds, the relationships between the hyperfine field and ordered magnetic moment obey a linear correlation as shown in Fig. 7.5. The hyperfine coupling constant of the uranium compounds is about l50T//i,B. 

Measurements of the magnitude of the magnetic Hyperfine Field by Mossbauer spectroscopy revealed small values at small interatomic distances and much larger values at... 

Ban] Mossbauer spectroscopy Magnetic properties (hyperfine field distribution), Cr2oFes4Ni26, from 13 to 295 K... 

Mossbauer spectroscopy has also been used to elucidate the magnetic structure in several amorphous alloys of Dy and 3d metals (Arrese-Boggiano et al., 1976 Chappert, 1979). In these cases, too, several of the Mossbauer lines were found to be broadened if compared to crystalline materials of about the same composition. Results for Dy-Fe alloys are reproduced in fig. 87. Arrese-Boggiano et al. first derived the distribution in magnetic hyperfine fields from the widths of those lines that are not affected by the quadrupole interaction (see fig. 85). The results were used subsequently in the determination of the distribution of the quadrupole interaction from the width of the remaining lines. The magnetic structures proposed by these authors correspond to Dy moments essentially distributed over all directions within a hemisphere (see also section 6.2.1). 

Mossbauer Absorption Spectroscopy. Spectra were acquired at room temperature in a constant acceleration spectrometer using a Co in Rh source. Isomer shifts are relative to the NBS standard sodium nitroprusside. Magnetic hyperfine fields were calibrated with the 515 kOe field of a-FcjO, at RT. Mossbauer parameters were determined by fitting the collected spectra with reference sub-spectra consisting of Lorentzian-shaped lines using a non-linear iterative minimization routine. 

A more promising quantity to be measured in this aspect seems to be the magnetic hyperfine field (Bhf). which can be probed layer by layer because of the isotope specificity of the Mossbauer spectroscopy (MS) (at least in the case of Fe films and surfaces). This is important in view of the expected oscillating character of Bhf close to the surface and its dependence on temperature, which exactly follows the temperature dependence of magnetization. 

The third prominent interaction in iron Mossbauer spectroscopy is the magnetic hyperfine interaction of the Fe nucleus with a local magnetic field. As explained in detail in Chap. 4, it can be probed by performing the Mossbauer experiment in the presence of an applied external magnetic field. 

McCammon et al. have studied fine nickel particles using Ni Mossbauer spectroscopy [22]. The measured average hyperfine field of 10 nm particles at 4.2 K was 7.7 T for nickel foil, it was found to be 7.5 T. Application of an external magnetic field of 6 T caused a reduction of the hyperfine splitting to 1.5 T as a consequence of the negative hyperfine field at Ni nuclei. 

Mossbauer spectroscopy is also able to give local moment orientations, with respect to the crystalline lattice, or the correlations between moment orientations and local distortion axis orientations in a chemically disordered or amorphous material. This arises from the interplay between the structural (electric field gradient) hyperfine parameters and the magnetic hyperfine parameters. In this way, the spin flop Morin transition of hematite, for example, is easily detected and characterized (e.g., Dang et al. 1998). The noncollinear magnetic structures of nanoparticles can also be characterized. 

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