Microwave magnetic-transmission resonance in gadolinium

Transmission-resonance experiments are described in paramagnetic and ferromagnetic gadolinium with a Curie point $T_C\cong 289$ °K. In these experiments, utilizing the spin-transmission-resonance technique, transmission resonance occurs not by diffusion of spins, but by modulation of the microwave penetration depth under resonance conditions. The effect is related to "antiresonance" previously observed in some cases of ferromagnetic resonance, but is much more pronounced in the transmission technique. A simple theory, due to VanderVen, and the solution of the boundary-value problem, due to Alexandrakis, accurately describe the results for paramagnetic gadolinium, and the fitted data yield several experimental parameters, in particular the relaxation time, as well as the susceptibility and resistivity. However, preliminary results indicate that these theories are inadequate to describe the transmission signals in ferromagnetic cases, even though they are adequate to fit the conventional absorption-resonance signals.