An electron-spin-resonance study of substitutional disorder in -doped

Electron spin-resonance (ESR) spectra of ions in (CYA) crystals have been measured at X-band microwave frequency. The spectra are only observed below 50 K: they are very broad and easily saturated by low microwave power at 4.2 K. The ESR lines, which vary in position with orientation of the magnetic field relative to the crystalline axes, have been fitted to a tetragonal spin Hamiltonian with the principal components observed to be close to those of ions in and . The associated microwave absorption is due to the lowest crystal-field level of the ground state of the ion in CYA. The measured g-tensor components and for in CYA can be explained in terms of the ground-state wavefunction composed of and components of mixed by the crystal-field terms and . The inhomogeneous broadening of the asymmetric ESR lines reflects a distribution of g-values, which is produced by tilting the principal z-axis of the effective spin away from the crystal c-axis and a distribution of the ground-state spin levels in of the ions through the random occupation of ions at the appropriate site in the disordered CYA lattice.