Magnetism Diagrams for Transition Metal Ions

The study ofmagneticproperties as a method to determine molecularand electronic structure of the ground state has a long tradition, in particular as far as metal complexes and solids of the transition metals are concerned. In the early days of the development, the emphasiswas placedon the observation ofdeviationsfrom the "spin-only" magnetic moment, the underlying assumption being that the value of themomentatroomtemperaturewouldsufficetodetermine boththeoxidationstate of the metal and the stereochemistry of the complex. The increasing number of deviations from these simple rules shifted the interest of researchers to the more detailed study ofthe temperature dependence of the magnetic moment. Most of the experimentalresults was then limited to measurementson powderedsubstancesand totemperatures between 77 and 300 K. Although themajorityofdataarestillofthis type, magnetic studies down to or even below 4. 2 K have become more common within the last few years as the sophistication of the equipment has increased. In addition, the investigation of magnetic anisotropies and principal magnetic suscep- tibilities received a new impetus.In order to make the best possible use of the theory, magnetism diagrams based on calculations by the ligand field theory were produced. As a rule, these diagrams show the effective magnetic moment as a function of the temperature and of any N additional parameters of interest. The first magnetism diagrams applicable to d electronicconfigurationswerepublished 30 yearsago byKotani. Thesediagrams are limited to the configurations (t2g)N, N = 1 to 4, in octahedral symmetry.