Effective internal magnetic field

An explanation for the recorded measurements of the paramagnetic susceptibilities was sought in a simple molecular-field model, by postulating an effective internal magnetic field - - AM and using the results found for TmSb. 

On the other hand, internal magnetic fields at the iron nucleus arising from the magnetic moments of unpaired valence electrons can be much stronger than any applied field and their effect can easily exceed the quadrupole interaction. For instance, Mossbauer nuclei in magnetic materials such as metals or oxides may experience fields of 30-50 T even without applied field. Similarly, the typical... 

These spectra, taken at variable temperatures and a small polarizing applied magnetic field, show a temperature-dependent transition for spinach ferredoxin. As the temperature is lowered, the effects of an internal magnetic field on the Mossbauer spectra become more distinct until they result at around 30 °K, in a spectrum which is characteristic of the low temperature data of the plant-type ferredoxins (Fig. 11). We attribute this transition in the spectra to spin-lattice relaxation effects. This conclusion is preferred over a spin-spin mechanism as the transition was identical for both the lyophilized and 10 mM aqueous solution samples. Thus, the variable temperature data for reduced spinach ferredoxin indicate that the electron-spin relaxation time is around 10-7 seconds at 50 °K. The temperature at which this transition in the Mossbauer spectra is half-complete is estimated to be the following spinach ferredoxin, 50 K parsley ferredoxin, 60 °K adrenodoxin, putidaredoxin, Clostridium. and Axotobacter iron-sulfur proteins, 100 °K. 

The first term in Eq. (II.1) is due to the effect of internal magnetic fields at the site of the nucleus in the crystalline substance under investigation. 

Nuclear spins are sensitive to the chemical environment of a nucleus. Electrons moving near the nucleus establish an internal magnetic field that modifies the local effective field felt by each proton to a value different from that of the externally applied field. The resulting chemical shift causes protons within different structural units of the molecule to show NMR peaks at different values of magnetic field. All protons in chemically equivalent environments will contribute to a single absorption peak in the spectrum. The relative area under each absorption peak is proportional to the number of protons within each equivalent group. In order to standardize procedures, chemical shift values are recorded relative to the selected reference compound tetramethylsilane (TMS) by adding a very small amount of... 

Starting with the simplest case, when no electric quadrupole interaction is present and when either an externally controllable magnetic field, Ho, is applied or, as in the case of metallic iron, when there is an internal magnetic field, Hint, we shall be concerned with Zeemann splittings of the nuclear levels as indicated in Table 1. The energy level positions Em are then dependent upon the effective magnetic field etf =i o + int ... 

The total spin-density imbalance is also affected by change in volume, so that there is a small effect on an internal magnetic field with pressure [13] (see Section 3.5). Compression can also affect the quadrupole splitting by decreasing the radial extent of the valence electrons, but redistribution of electrons between the different orbitals may also occur. 

From the foregoing description of the origins of the internal magnetic field, it might be assumed that all compounds containing unpaired valence electrons would show a hyperfine magnetic splitting effect. There is, however,... 

In the disordered iron-rich alloys (0-10 at. % Si) nearest-neighbour effects from Fe atoms with 8, 7, and 6 Fe neighbours are found, analogously to the dilute Fe-Al disordered alloys [31, 102, 103]. The internal magnetic field decreases stepwise as the number of Si neighbours increases. The alloys with 14-27 at. % Si are ordered in the FesAl-type lattice. Once again the decrease in field and small increase in chemical isomer shift are compatible with a transfer of electrons to the iron 3[Pg.322]

If the point symmetry group of the lanthanide ion does not possess an inversion, the magnetization linear in an external electric field may be observed, and the dielectric susceptibility of the sample may be also radically affected by an external or internal magnetic field. Electric field effects on the EPR spectra of the lanthanide ions in insulators are well known (see, for example, Sakharov 1979, 1980), and here we shall consider only the alteration of the dielectric properties of the crystal due to the ordering in the lanthanide subsystem. Dielectric measurements are often used to plot the phase boundaries of the lanthanide magnets in the magnetic field. The eneigy of the lanthanide ion in the quasistatic electric field is presented in eq. (9). The effective even dipole moment of the ion can be written as follows... 

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