Mössbauer spectroscopy of magnetic small particles with emphasis on barium ferrite

Ferromagnetic and ferrimagnetic particles have been of scientific and technological interest for several decades. The study of nanometer clusters or particles is currently a developing subject. Such materials may be in a non-equilibrium or quasi-equilibrium phase; different properties as compared to the bulk and indeed even new physical phenomena may be expected. Some ways to synthesize clusters and fine particles are described. Mössbauer spectroscopy is shown to be particularly useful for the study of nanometer particles; an outline of how it actually works is given. As an illustration, barium ferrite small particles, a material of topical interest, is considered in detail. In particular, methods of preparation, the crystal and magnetic structure, the magnetic characteristics, recently obtained Mössbauer results, and potential and realized applications are reviewed.     

61Ni Mössbauer spectra of fine Ni particles

We report the first measurements of fine Ni particles from⁶¹Ni Mössbauer spectroscopy. The average hyperfine field of the 10 nm particles at 4.2K is measured to be 7.7(4) T, compared to the measured value for Ni foil of 7.5(3) T. Application of an external field of 6 T to the fine particles causes a reduction of the hyperfine splitting to 1.5(6) T, a consequence of the negative hyperfine field at Ni nuclei. These results are discussed in terms of fine particle effects.     

Low-temperature Mössbauer studies of FeNb2O6

Fe⁵⁷ Mössbauer spectra of FeNb₂O₆ were obtained from 15.0K down to 1.9 K. The isomer shift, 1.42±0.01 mm sec^?1 relative to Cr, was found to be temperature independent, whereas the magnitude of the quadrupole splitting was observed to decrease slightly with temperature. The quadrupole splitting and the hyperfine field at 1.9 K are -2.41±0.01 mm sec^?1 and 34.6±0.3 kOe respectively. The directions of the hyperfine fields experienced by the Fe nuclei are in the a-c plane symmetrically displaced with respect to the crystallographic axes.     

Design and synthesis of a diverse morpholine template library

Efficient and general procedures have been developed for the solution-phase preparation of substituted morpholine derivatives, and a library has been produced around generic structure 1. This library was designed with proprietary modeling software for use as a general screening library. The 30 R1 reagents were phenols, and the 275 R2 reagents were taken from five different reagent classes, giving a variety of product classes in the final library of 8250 potential products. All of the library members were generated from a common intermediate, mesylate (5), which was synthesized efficiently, in bulk, in three steps from N-benzylethanolamine (2). High-throughput chemistry using robotics was carried out to produce the 7907 library members, which were individually characterized by reversed-phase LC/MS analysis.     

On the hyperfine field of γ-Fe2O3 small particles

The smaller magnetic hyperfine field of γ-Fe₂O₃ small particles below the superparamagnetic blocking temperature compared to that found in larger crystals is discussed in terms of surface and of intrinsic size effects by using Mössbauer spectroscopy.     

Magnetic structure of ion-implanted bubble garnets

The surface magnetic structure of bubble garnet films implanted with 80 keV Ne⁺ ions has been investigated by conversion-electron Mössbauer spectroscopy in conjunction with backscattered X-ray Mössbauer spectroscopy. For lower doses (～1–3 × 10¹⁴Ne⁺cm^-2) a ferrimagnetic component with in-plane magnetization coexists with a smaller paramagnetic phase in the implanted layer; for a dose of 5 × 10¹⁴Ne⁺cm^-2 only a paramagnetic phase is observed.