Transmission electron spin resonance in dilute rare-earth aluminum alloys

We report transmission-electron-spin-resonance (TESR) measurements on dilute alloys of Er, Tm, and Lu in aluminum. We have derived theoretical expressions for the effects of the exchange and crystal-field interactions on the resonance properties of the Er and Tm alloys. A computer fit of these expressions to the data yields values for the crystal-field parameters and the sign, magnitude, and a measure of the $k$ dependence of the exchange interaction for each alloy. Combining the TESR results with direct EPR measurements on Al:Er, we obtain the free-ion $g$ value of ${\mathrm{Er}}^{3+}$ and a measure of the electron-electron enhancement in the host. The TESR measurements also yield the outer-shell spin-flip scattering cross sections ${\sigma }_{\mathrm{sf}}$ for Er, Tm, and Lu. Corresponding resistivity measurements indicate that the outer-shell scattering properties of these impurities are quite similar, in that they are all characterized by roughly the same value for the ratio $\frac{{\sigma }_{\mathrm{sf}}}{{\rho }_r}$.