Magnetic Evans balance

The most common way to ascertain the magnetic properties of materials is to measure their molar magnetic susceptibility, The magnetic susceptibility is related to the effective magnetic moment according to Equation (15.10) and is mea-sured using either a Gouy balance or an Evans balance. 

Grind your prepared complex into a fine dry powder and pack it into the tube of a Gouy or Evans balance and measure its magnetic susceptibility and hence its effective magnetic moment and suggest its structure. 

A room temperature magnetic moment of S.9 PB is observed. The manual of the commo cial Evans balance gives data for Mn(Il) chloride. 

Various adaptations that rely on force methods have been commercialised (the so-called Evans-Johnson-Matthey balance) or designed from readily available parts and described in the literature. The Evans method uses NMR and can provide variable temperature data on molecules in solution, but the technique is limited to a window where solvents stay liquid and solutes stay in solution. The one development that has been crucial to the more recent rapid development of this research field is the availability of relatively inexpensive and easy-to-use, variable temperature, variable field instrumentation, specifically the Superconducting Quantum Interference Device (SQUID) magnetometer. With a SQUID, it is possible, even for relatively inexperienced users, to determine the magnetic properties of a sample (typically 10-20 mg) as a function of temperature and applied field (down to 1.8 K and... 

Evans, D.F. J. Chem. Soc. (A) 1%7,1670. Simple Gouy-Rankine magnetic balance. 

Prepare or use a magnetic susceptibility standard in the Gouy balance or the Evans instrument. Use the standard to find the constant C in the eqn. 2.6 or C in eqn. 2.11. Grind each of the prepared complexes to a fine powder. Pack the balance tube with the powder to the mark and follow the instructions as in Sec.2.1.3. Calculate the magnetic susceptibility and the effective magnetic moment of each powder and comment on your results. 

Magnetic susceptibilities were determined with a Gouy balance or using a nmr method originally employed by D.F. Evans (1959). This last method has been used successfully with minor modifications for some organolanthanides (D.F. Evans, 1971). The nmr method, which is very simple to use, is quite applicable in the case of species soluble in an organic medium. 

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