Electron spin resonance studies of Cr3+ impurities in soda alum

The electron spin resonance of Cr3+ impurities was studied in two types of crystals which grew out of a saturated solution containing a mixture of sodium sulfate, aluminum sulfate, and chromium sulfate dopant. One of the crystals was identified as soda alum, NaAl(SO4)2∙12H2O, which has cubic symmetry, while the other was a monoclinic crystal of undetermined structure. In soda alum, four differently oriented, but otherwise equivalent, magnetic complexes of chromium were found. Each complex exhibited an axial distortion along one of the crystal body diagonals. In the monoclinic crystal, two differently oriented, but otherwise equivalent, magnetic complexes of chromium were found. Each of the complexes exhibited a strong rhombic distortion but none of the magnetic axes coincided with the crystallographic axes. However, the complexes were related by twofold symmetry to the monoclinic b axis. The ESR results of the two crystals were fitted to suitable spin Hamiltonians and the pertinent parameters were determined. The crystallographic parameters (a, b, c) of the monoclinic crystal were determined by X-ray analysis.