Crystal fields magnetism

There has been a considerable effort in the physics and chemistry communities to use INS methods to study magnetic dynamics, which can often be described as spin waves. Measurements of spin wave dispersion curves can provide information about the interactions between atomic magnetic moments, the so-called exchange interactions. There have been comparatively few INS measurements on magnetic minerals. INS methods have been used to produce spin wave dispersion curves for hematite. Crystal field magnetic transitions in cobalt bearing cordierite, and spinel phases have also been studied by INS. ... 

The magnetic properties of Pu compounds in different oxidation states are reviewed. New measurements on Pu(C8H8)2, PuFi, [(C2Hs)itN]2PuCl6, and [ (C2H5)itN]itPu(NCS)s are presented. The interpretation of the data is based on intermediate, j-j mixed crystal field states and orbital reduction due to covalency. Especially in the case of the organometallic compounds a large orbital reduction is found. 

Due to the intermediate coupling the sign of the crystal field matrix element 6 is reversed compared to the pure Russell-Saunders state. Thus for 8-fold cubic coordination a F7 ground state was found. From EPR measurements on Pu3"1" diluted in fluorite host lattices, a magnetic moment at T=0 K can be calculated, ranging from li ff = 1.333 (in Ce02) to y ff = 0.942 (in SrCl2) (24,... 

As seen in Fig. 8 the experimentally determined magnetic moments at room temperature are in general much lower than the free ion values. To extract the contribution of orbital reduction, the influence of intermediate coupling, crystal field effects and j-j mixing must be considered. 

K over the temperature range 6 to 40°K. Below 6°K, the deviation of the data from the straight line indicates lower crystal field levels. At higher temperatures, the magnetism becomes too weak to measure by the magnetometer. 

The effects of the bonding electrons upon the d electrons is addressed within the subjects we call crystal-field theory (CFT) or ligand-field theory (LFT). They are concerned with the J-electron properties that we observe in spectral and magnetic measurements. This subject will keep us busy for some while. We shall return to the effects of the d electrons on bonding much later, in Chapter 7. 

There will exist an equilibrium between the two states. If the ener between the two states, E, is of the order of kT, then the relative populations of the two states will vary with the temperature of the sample. In the Fe(III) dithiocarbamate series of complexes, [FeCRiRgdtcla], AE can be varied by suitable choice of substituents Ri and Rj. Although these are well removed from the FeSg molecular core, they can appreciably affect the electronic parameters of the central iron atom and of the surrounding crystal field of the sulfur atom by way of the conjugated system of the ligand (237). The results of the spin crossover are reflected in magnetic susceptibility data. 

FefNOafa 9H2O, which are connected by a screw dyad axis parallel to the [010] direction. The crystal field axes Z[ and Zj form the angles 61 and O2 with the applied magnetic field. (Reprinted with permission from [41] copyright 1978 by Elsevier)... 

In amorphous frozen solutions with only one type of species (e.g. [Fe(H20)g] ) the crystal field interaction of the Fe " ions may be similar, but the orientations of the crystal field axes in general differ. When magnetic fields are applied, this... 

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