Resonance fields, angular dependence

FIGURE 5.5 Angular dependency of axial y-value. The angle 0 between B0 and the molecular z-axis and the axial value are plotted versus the resonance field for a typical tetragonal Cu(II) site with gN = 2.40 and g = 2.05 v = 9500 MHz. 

In Fig. 11 is plotted the angular dependence of the resonant magnetic field for chromium(lll) acetylacetonate in a single crystal of the cobalt(III) compound. This system has hv0 D for an -band spectrometer. The orientation of the crystal was that of orientation II in Fig. 6, in which the magnetic field is in the plane defined by the threefold symmetry axes of the two molecules in the unit cell. The angle given in Fig. 11 is the angle between... 

In a system of nanoparticles, thermal fluctuations of their magnetic moments severely reduce the anisotropy of the resonance magnetic field, resulting in superparamagnetic spectra narrowing. This reduction is the more pronounced the smaller is the particle size. Therefore, the SPR spectra of macroscopically isotropic nanoparticle systems characterised by a distribution in size usually maintain a distinct shape asymmetry characteristic of powder patterns of randomly oriented anisotropic particles. From an inspection of such spectra, one can conclude that the angular dependence of the resonance magnetic field of individual particles is not completely reduced. 

Figure 7. Angular dependence of the resonance field of the 11B-NMR spin echo spectrum in the commensurate phase. B c-axis. 0 is the angle between the crystal o-axis and the applied-field direction.

Secondly, in both cases of the films specific angular dependence of the resonance field is observed especially for the films obtained in external MF. As one can see (Figure 4) the additional peak of EMR spectra of magnetic films form imder MF action shifts toward lower field if the measuring field is parallel to the sample plane and towards higher if the field is perpendicular. The orientation dependence of the shape of EMR line and its resonant position results from the predomination of imiaxial type of magnetic anisotropy due to the formation of motionless anisotropic linear structures. 

According to the basic EPR resonance Equahon 1.9, the frequency required for the EPR transition depends only on B and Xb since the g value in this equation is isotropic. However, since the EPR spectrum in the solid state will depend on the relative orientation of the applied field with respect to the paramagnetic species in the powder. Equation 1.9 must be modified to include this angular dependence ... 

The angular dependence plots illustrating the variation in the resonant field positions are thus shown in Figure 1.10c. The most intrinsic feature in the powder pattern of a rhombic g tensor consists of the fact that while only very few orientations contribute to the spectrum at B gi and B g3 (single crystal-like case), several intermediate orientahons reveal the same resonance as B g2 resulting in a maximal absorption at this field. 

The orientational distribution fimction P (cos 0) enters the shape of the wideline spectrum 5(f2) in a slightly hidden way. The angular dependence of the resonance frequency is given by (3.1.23) via the orientation of the magnetic field in the principal axes system XYZ of the coupling tensor (cf. Fig. 3.1.2), while the orientational distribution function specifies the distribution of the preferential direction n in a molecule-fixed coordinate frame (Fig. 3.2.2(a)). Figure 3.2.3 shows the relationship between the different coordinate frames and the definition of the relative orientation angles. 

NMR can provide detailed information about type and timescale of slow molecular motion. Slow molecular reorientational processes can be probed by making use of the angular dependence (3.1.23) of the resonance frequency. Slow molecular translation can be investigated with NMR by measuring the particle diffusion and flow in magnetic field gradients (cf. Section 7.2.6) [Call, Cal2, Karl, Kiml, Stil]. 

Fig. 7.19 The angular dependence of the ESR resonance fields 6q for triplet exdtons in anthracene crystals on rotating Bq in the plane b = 0. = 2jt 35 GHz, T= 300 K. After [17],...

Fig. 7. Angular dependence in the ab plane of the average fields for resonance in the high-held ODMR spectrum of C-benzophenone in 4,4 -dibromodiphenylether showing that the principal transverse axes of g are parallel to the corresponding axes of D and that g,, - < g,y (Mucha, 1974).

Fig. 1. Angular dependence of the resonance magnetic field of Tm nuclei in a TmES crystal at a temperature of 4.2 K and a resonance frequency of 7.5 MHz.

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