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Rare-earth doped crystals of lanthanum oxysulfide were found to exhibit strong photoconductivity which increases rapidly with temperature. Correlation of photoconductivity to luminescence spectra of La2O2S : Eu shows that thermal quenching of the luminous emission from 5D states leads to the production of photocarriers, the majority of which are most likely holes. Special features of La2O2S : Eu photoconductivity indicate the important role which the charge-transfer states play in the luminescence mechanisms.

The excitation of microwave ultrasonics by ferromagnetic resonance in magnetic thin films at 10 Gc/sec has been analyzed on the basis of a spatial inhomogeneity in the internal field as treated by Kooi.1 Four types of magnetoelastic interaction processes were studied experimentally in thin Permalloy films at X band: phonon excitation by spin waves (M→P), spin-wave excitation by phonons (P→M), re-excitation of spin waves by phonons which were originally produced by spin waves (M→M) and the attenuation of piezoelectrically generated and detected phonons by spin waves (P→P). Observations were made in films with compositions varying from 77% Ni to 85% Ni. In each film distinct spin-wave modes were observed and a one-to-one correspondence between the spin-wave modes and the phonon modes could be determined. A value for the magnitude of the transverse magnetoelastic constant was obtained from the measurements of the P→P process. Using the measured value of b2, conversion coefficients were computed for the M⇆P and M→M processes. Comparison with experiment yields a discrepancy of approximately 5 dB for the M⇆P processes and about 15 dB for the M→M process for the modes n<6. The calculated value of the magnetoelastic constant, the mode number dependence of the spin-wave—phonon interaction intensities for the M⇆P and M→M processes, and the frequency dependence of the M→M process strongly favor the volume inhomogeneity model over the surface spin pinning model. The results of this work are reported in greater detail elsewhere.2

The intensities of paramagnetic resonance lines in SrTi0 3 have been correlated to the iron concentrations. Evidence for attributing the origin of the resonance in titanates to iron impurities (Fe 3+ ) rather than to the domain structure was obtained. In SrTi0 3 , resonance experiments over the temperature range 300°K to 1.9°K show a slow continuous increase of the tetragonal component of the crystalline field down to the ferroelectric region. From intensity considerations the absolute signs of the crystalline splitting parameters have been determined.

Using the group-theoretical approach of Blume and Orbach, a Hamiltonian is derived for interaction between coherent acoustic waves and rare-earth ions in cubic coordination. This Hamiltonian is found in partial agreement with the phenomenological spin-phonon Hamiltonian for effective spin 5=\ ions. Observations were made of the transmission of longitudinal and transverse 10-kMc/sec acoustic waves through rare-earth-doped CaF 2 as a function of an applied magnetic field. Magnetic-field-dependent attenuation of acoustic waves was observed for only two ions, Eu 2+ and Dy 3+ . In other cases only the upper limits of the acoustic absorption could be determined, and from these, lower limits of the direct-process relaxation time T\ were estimated. These lower limits were found approximately three orders of magnitude longer than the T\ values measured in CaF 2 at liquid-helium temperatures by the conventional pulse-saturation technique; an explanation of the discrepancy for some cases is suggested.146 268