Diamagnetic field

Figure 2 The Meissner Effect, or the levitation of a strong magnet by the internal diamagnetic field of a high Te superconductor. 

Comparison of our results with the correlation curve for OHO bridges shows that the [NHN]+ curve s maximum is shifted toward higher values of (5 and the isotope effect is somewhat higher. The difference between OHO and NHN in DMAN H+ cations, reflected in Fig. 19.4, may result from two effects. The first, discussed by Scheiner [10, 33], is due to different covalent radii and a slightly different charge distribution. The second effect should be ascribed to the diamagnetic field of the naphthalene 7t-electron system. 

The diamagnetic field is associated with the electronic ground state wave-function in the absence of an external field, is generally aligned in a direction nearly antiparallel (opposite) to that of the external field, and tends to cause an upfield shift of the nuclear resonance. The paramagnetic field is associated with the perturbed electronic functions, is generally in a direction nearly parallel with the external field, and tends to cause a downfield shift. 

It was shown in Section 5.2 that the diamagnetic field is proportional to the external magnetic field and is in the opposite direction to it. Thereby,... 

The two primary causes of shielding by electrons are diamagnetism and temperature-independent paramagnetism (TIP). Diamagnetism arises from the slight unpairing of electron orbits under the influence of the magnetic field. This always occurs so as to oppose the field and was first analysed by Lamb [7]. A simplified version of his fomuila. 

Other frequently used resonators are dielectric cavities and loop-gap resonators (also called split-ring resonators) [12]. A dielectric cavity contains a diamagnetic material that serves as a dielectric to raise the effective filling factor by concentratmg the B field over the volume of the sample. Hollow cylinders machmed from Ilised quartz or sapphire that host the sample along the cylindrical axis are conunonly used. 

It is a white crystalline, brittle metal with a pinkish tinge. It occurs native. Bismuth is the most diamagnetic of all metals, and the thermal conductivity is lower than any metal, except mercury. It has a high electrical resistance, and has the highest Hall effect of any metal (i.e., greatest increase in electrical resistance when placed in a magnetic field). 

The NMR spectrum of the syn isomer shows evidence of a diamagnetic ring current, based on both the relatively low-field position of the vinylic hydrogens and the upfield shift of the methylene hydrogens. The anti isomer shows much less pronounced shifts. The X-ray crystal structure of the syn isomer shows a moderate level of bond alternation, ranging ftom 1.36 to 1.45 A (Fig. 9.4A). In the anti isomer, bond alternation is more pronounced, vith the double bond in the center ring being essentially a localized double bond (Fig. 9.4B). 

---