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The results of electron spin resonance experiments on a series of transition metal ions in single crystals of corundum are reviewed and interpreted in terms of crystal field theory emphasizing three topics: (1) The strength of the cubic crystal field, (2) the axial field as an indicator of position of the impurity ion, and (3) Jahn-Teller effects in the ground state. The 4d and 5d ions which were examined, i.e., Ru3+, Rh3+, and Ir3+ are found to be strong crystal field cases. In addition, the increased charge of Ni3+(3d7) is shown to be sufficient to drive it to a strong crystal field case (t26e) with S = ½ compared to Co2+ (3d7) which is t25e3 with S = 32. The parameter v which measures the trigonal field potential, was found to be +850 cm−1 in Ru3+ in good agreement with other ions such as Co2+ and V3+ whose cubic field ground states are also orbitally degenerate. In contrast, the determination of v from ESR data on ions with singlet ground states such as Cu3+ and Ni2+ is regarded as less reliable. The Jahn-Teller effect was observed for Pt+ (or Pt3+), Ni3+, and Cu2+.

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A new approach to critical dynamic scaling of g" is presented wherein P/zv, zv, and T, may all be separately determined independent of each other. Application is made to Cdo.6Mn0. 4Te where by use of this new procedure it is shown that the data in the critical region above T, are inconsistent with activated dynamics. This new procedure applied to other systems, reveals frequent underestimates of zv and overestimates of T,. Apparent systematic deviations from scaling which are found near and below T, are brie8y discussed.Dynamic scaling of the ac susceptibility Z'(tu, T) +iZ"(m, T) has been used extensively as supporting evidence for critical behavior associated with phase transitions in random magnetic systems. In conventional dynamic scaling the relaxation time z is related to the correlation length g-( t ( " via r-g'-)

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