Electron-Spin Resonance of Rare Earths in Aluminum

The electron-spin resonance of Gd, Dy, and Er has been observed in dilute Al-based alloys. From the temperature-dependent linewidth and the sign of the $g$ shift, a value of the exchange integral $J_{f-s}=+0.11\mathrm{}\pm 0.02$ eV was extracted for Al: Dy and Al: Er. This value is in agreement with that extracted from the reduction of $T_c$ in Al: Er, on the assumption of little influence of the crystalline field. The more concentrated Al: Gd alloys exhibited a strong magnetic-resonance bottleneck, which was partially opened by (i) reduction of the Gd concentration and (ii) by introducing a third element. The exchange integral was found to equal $J_{f-s}=+0.17\mathrm{}\pm 0.03$ eV for Al: Gd, and values were obtained for the spin-lattice relaxation rate of the conduction electrons from band effects, the Gd impurities themselves, and the third elements (Ag, Au). A "residual" positive $g$ shift $\Delta g_1=+0.05\mathrm{}$ was noted for Al: Gd (as well as for a number of other dilute Gd alloys), and is tentatively attributed to polarization of the screening electrons of $d$-like character.