We report on the theoretical and experimental study of spin-dependent electronic transition rates which are controlled by a radiation-induced spin-Rabi oscillation of weakly spin-exchange and spin-dipolar coupled paramagnetic states ($S=\frac{1}{2}$). The oscillation components [the Fourier content, $\mathbf{F}\left(s\right)$] of the net transition rates within spin-pair ensembles are derived for randomly distributed spin resonances, with an account of a possible correlation between the two distributions corresponding to individual pair partners. Our study shows that when electrically detected Rabi spectroscopy is conducted under an increasing driving field $B_1$, the Rabi spectrum, $\mathbf{F}\left(s\right)$, evolves from a single peak at $s={\Omega }_R$, where ${\Omega }_R=\gamma B_1$ is the Rabi frequency ($\gamma$ is the gyromagnetic ratio), to three peaks at $s={\Omega }_R$, $s=2{\Omega }_R$, and low $s\ll {\Omega }_R$. The crossover between the two regimes takes place when ${\Omega }_R$ exceeds the expectation value ${\delta }_0$ of the difference in the Zeeman energies within the pairs, which corresponds to the broadening of the magnetic resonance by disorder caused by a hyperfine field or distributions of Landé $g$ factors. We capture this crossover by analytically calculating the shapes of all three peaks at an arbitrary relation between ${\Omega }_R$ and ${\delta }_0$. When the peaks are well developed their widths are $\Delta s\sim {\delta }_0^2/{\Omega }_R$. We find a good quantitative agreement between the theory and experiment.

• Received 30 July 2012

DOI:https://doi.org/10.1103/PhysRevB.87.155208