Ferromagnetic resonance , metal

For ferromagnetic cobalt particles in zeolite X, spin-echo ferromagnetic resonance has been used to obtain unique structural information (S6). In addition, study of the catalytic signature of metal/zeolite catalysts has been used by the groups of Jacobs (87), Lunsford (88), and Sachtler (47,73,89). Brpnsted acid protons are identified by their O—H vibration (90,91) in FTIR or indirectly, by using guest molecules such as pyridine or trimethylphosphine (92,93). An ingenious method to characterize acid sites in zeolites was introduced by Kazansky et al., who showed by diffuse reflection IR spectroscopy that physisorbed H2 clearly discerns different types of acid sites (94). Also, the weak adsorption of CO on Brpnsted and Lewis acid sites has been used for their identification by FTIR (95). The characterization of the acid sites was achieved also by proton NMR (96). 

Another route to trapping small Fe and Co particles within the supercages of faujasite zeolites is the metal vapor solution condensation ( metal atom solvate ) method, used by Nazar and Ozin 148). When characterized by Fe Mossbauer and ferromagnetic resonance spectroscopies, Fe particles in the size range of 5-12 A are located in the zeolite supercage and its 12-member ring entrance. In using these Fe -NaY or Co -NaY catalysts for... 

Ferromagnetic resonance (FMR) spectra of cobalt metal were recorded at X-band frequencies on a Vartan E-4 spectrometer. DPPH and weak pitch were used as standards for g factor. Transmission electron microscopy (TEM) was done with JEOL 200CX microscope using 160 KeV electrons. 

The technique using non-magnetic metallic single crystals in NMR was long ago introduced by Jones and Williams (1962), when they analysed the anisotropy of the nuclear magnetic resonance in white tin. It is only 14 years ago, however, since the techniques appropriate for the NMR of ferromagnetically ordered metallic single crystals were introduced by Fekete et al. (1975). However, the requirements for the sample preparation are relatively severe. Otherwise the full... 

Morke W., Lumber R., Schubert U., Breitscheidel B. Metal complexes in inorganic mataials 11 composition of highly dispersed bimetallic Ni Pd alloy particles prepared by sol-gel processing electron microscopy and ferromagnetic resonance study. Chem. Mate. 1994 6 1659-1666... 

Finally, the use of simple valence bond theory has led recently to a significant discovery concerning the nature of metals. Many years ago one of us noticed, based on an analysis of the experimental values of the saturation ferromagnetic moment per atom of the metals of the iron group and their alloys, that for a substance to have metallic properties, 0.72 orbital per atom, the metallic orbital, must be available to permit the unsynchronized resonance that confers metallic properties on a substance.34 38 Using lithium as an example, unsynchronized resonance refers to such structures as follows. 

The model of a degenerate gas of spin polarons suggests that if the direct or RKKY interaction between moments is weak and EF too great to allow ferromagnetism then the moments might all resonate between their various orientations. This would mean that it is possible in principle to have a heavily doped magnetic semiconductor or rare-earth metal in which there is no magnetic order, even at absolute zero. This possibility is discussed further in Section 8 in connection with the Kondo effect. 

XPS measurements demonstrated that loaded Ni is predominantly located between the layeres of the catalyst and little remains on the external surface.15) For sensitivity reasons, a sample with 1 wt% Ni-loading was used. Comparison of the Ni2p3/2 peak intensity in the catalyst with that in a reference sample (which was also 1% Ni-loaded KNb03 with almost the same BET surface area as that of K4Nb6017) has shown that the surface concentration of Ni in the former is about 100 times less than that of the reference sampled EXAFS spectra for 1 wt% Ni-loaded samples both before and after the reduction procedure, as well as for Ni and NiO as standards, indicated that after reduction by H2 at 500°C for 2 b the loaded Ni was completely reduced to the metallic state.15) Even after reoxidation by 02 at 200°C for 1 h, most of the Ni remained metallic. (By XPS, the Ni, which remained on the external surface, was found to be in the oxidized form.) The formation of metallic nickel on a 0.1 wt% Ni-loaded catalyst was also confirmed by ESR measurements.7 The appearance of an intense resonance line after the reduction and reoxidation indicates the formation of ferromagnetic metallic nickel in the sample. 

Electron paramagnetic resonance experiments also support the existence of ferromagnetic iron particles. X-ray powder diffraction experiments, electron microscopy, and surface analysis measurements show the existence of both metals on the surface before and after reduction. We know the particle size again is quite large, although there is a wide digtribution in these samples, ranging from 30 A to about 150 A. 

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