27 No. 3
Practical Guide to Measurement and Interpretation of Magnetic Properties (IUPAC Technical Report)
S. Hatscher, H. Schilder, H. Lueken, and W. Urland
Pure and Applied Chemistry
Vol. 77, No. 2, pp. 497-511 (2005)
In today’s magnetochemistry, superconducting quantum interference device (SQUID) magnetometers are widely used. Automated measurements of high accuracy are state of the art and have the aim to fully characterize magnetic properties of compounds and materials. The findings serve to determine electronic configuration of the magnetic center, interatomic exchange interactions, diamagnetic contributions, metallic character, superconductivity, spin-glass behaviour, superparamagnetism, and more. To take full advantage of experimental data, special attention should be given to: appropriate units, purity of the sample, measurement conditions, suitable graphical presentation of the results, and adequate models. This practical guide collects subjects that should be taken into consideration in order to present reliable magnetochemical results in a standardized way, to allow correct statements about the electronic structure of the substance under investigation, and to allow comparison between measurements. We presuppose that the reader is familiar with the basic laws and terminology of magnetochemistry.
This report points out rules to protect the magnetochemist from pitfalls in both measurement and interpretation of magnetic data. Carefully chosen magnetic field strengths during magnetic susceptibility measurements guarantee the recording of genuine data. With the help of examples, the effect of too strong applied fields is demonstrated producing magnetic saturation and, for example, quenching of weak ferro- or antiferromagnetic spin-spin couplings. In consequence, the data run the risk of being misinterpreted unless model susceptibility equations are applied that take the field dependence of χm into consideration. Recommendations are given for the presentation of experimental and theoretical data. The limited applicability of the most overworked formula in paramagnetism, the Curie-Weiss law χm = C/(T –θ), is clearly presented (magnetically condensed systems, pure spin magnetism). While rough and ready susceptibility formulae are applicable to specific 3d and 4f systems, the complex situation for the remaining d and f centers, including actinides, demands computer programs that consider simultaneously interelectronic repulsion, ligand field potential, spin-orbit coupling, interatomic exchange interactions, and applied magnetic field.
last modified 7 April 2005.
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