Paramagnetic field dependence

The reaction of bis(benzene)vanadium [12129-72-5] with TCNE affords an insoluble amorphous black soHd that exhibits field-dependent magnetization and hysteresis at room temperature, an organic-based magnet (12). The anion radical is quite stable in the soHd state. It is paramagnetic, and its intense electron paramagnetic resonance (epr) spectmm has nine principal lines with the intensity ratios expected for four equivalent N nuclei (13) and may be used as an internal reference in epr work (see Magnetic spin resonance). 

Powder spectra of paramagnetic compounds measured with applied fields are generally more complicated than those shown in Fig. 4.14. Large internal fields at the Mossbauer nucleus that are temperature- and field-dependent give rise to this complication. If, however, the measurement is performed at sufficiently high temperature, which is above ca. 150 K, the internal magnetic fields usually collapse due to fast relaxation of the electronic spin system (vide infra, Chap. 6). Under... 

In large applied magnetic fields at low temperatures, the ionic spins in a paramagnetic sample are to a large extent aligned and this leads to a field-dependent narrowing of the distribution of dipolar fields, i.e. and (Air ) decrease with... 

Fig. 16. Magnetic field dependence of the resistivity for a 200-nm thick film of Ga Mn.t As with x = 0.053 in the high-temperature paramagnetic region. The solid lines show the fitting using eq. (2) (Omiya et al. 2000).

When any substance is placed in a magnetic field, the field produced within the sample will either be greater than or less than the applied field, depending on whether the material is paramagnetic or diamagnetic. The difference between the two (A//) can be expressed as... 

The information content of nuclear longitudinal relaxation measurements in both paramagnetic and diamagnetic systems can be greatly increased by performing such measurements as a function of the magnetic field. For paramagnetic species, the reason is apparent from the functional form of the equations discussed in Chapter 3 and from the relevant experimental data, reported in Chapter 5. The field dependence of a relaxation rate is called relaxation dispersion, and is abbreviated as NMRD. In principle, NMRD would be helpful for any chemical system, but practical limitations, as will be shown, restrict its use, with a few exceptions, to water protons. 

The third-rank diamagnetic and paramagnetic contributions to electric field dependent magnetic susceptibility and nuclear magnetic shielding, to first order in... 

---