Paramagnetic susceptibility, related magnetic moment

Magnetic susceptibilities of solutions — These are useful parameters for determining equilibrium constants for reactions involving spin changes. The Evans nmr method utilizes the observed shift in the resonance line (say of a proton of t-BuOH or hexamethyldisilox-ane) in solution when a paramagnetic substance is added. The paramagnetic shift A/ is related to the magnetic moment (jj, of the solution at TK by the approximate expression... 

The magnetic susceptibility is thus a temperature-dependent property of a bulk substance. It is meaningless to specify the susceptibility of a single molecule or complex ion. For convenience, inorganic chemists prefer to answer the question How paramagnetic is this substance in terms of the magnetic moment peff defined by the relation ... 

Example 6. For paramagnetic materials the magnetic susceptibility may be measured experimentally and used to give information on the molecular magnetic dipole moment, and hence on the electronic structure of the molecules in the material. The paramagnetic contribution to the molar magnetic susceptibility of a material, xm, is related to the molecular magnetic dipole moment m by the Curie relation... 

In the chromia-alumina catalyst system we are primarily concerned with the phenomena of paramagnetism and antiferromagnetism, both of which are due to the magnetic moments of the chromium ions. The magnetic susceptibility (y) of a paramagnetic material such as chromia-alumina is related to the absolute temperature (T) according to the Curie-Weiss law... 

Another check is provided by the diamagnetic susceptibility Xm, of the molecules in the vapour state (Banyard i960). This is the sum of a paramagnetic term Xnt oe to the magnetic moment associated with excited states, which can be calculated from spectroscopic data, and a purely diamagnetic term Xr which is related to the electron distribution in the ground state by... 

In most molecules with symmetrically disposed orbits and paired spins the effects cancel out, but where there is an unbalanced moment a substance shows what are called paramagnetic properties, and orientates itself in line with a magnetic field. The susceptibility, of a body is defined by the relation y = IjH, where H is the applied field and I is the magnetic moment per unit mass. The magnetic moment is called forth by the field in so far as this orientates the permanent moments. Orientation becomes less easy as thermal motion increases, and consequently the susceptibility decreases with increase of temperature, sometimes in accordance with the law jT. 

Diamagnetic materials are not related to a magnetic moment on the atomic scale without magnetic field, in contrast to para- and ferromagnetic substances. In more than half of the elements of the periodic table, paramagnetism dominates and thus the susceptibility offers a positive value. 

---