Strong spin–phonon coupling in Gd-filled nanotubes

To develop one-dimensional spintronic devices, we synthesize Gd-filled double-walled carbon nanotubes where the long spin-coherence time of a paramagnetic gadolinium (Gd3+) ion and the discrete phonon modes of a carbon nanotube can be combined. Here, we report Raman observation of spin–phonon coupling in the Gd-filled double-walled nanotubes by analyzing the low-temperature dependence of the dominant phonon modes (G-band). A G-band (w+G ext and w +G int) phonon frequency hardening is observed below a critical temperature of TC ∼ 110 K coinciding with the onset temperature of superparamagnetic behavior confirmed through magnetization studies. This anomalous behavior is ascribed to phonon renormalization induced by spin–phonon coupling interaction. The estimated spin–phonon coupling constant values are 12.2 and 5.0 cm−1 for G +ext and G +int phonon modes, respectively, analyzed by comparing the phonon frequency variation (Δw) to magnetization as a function of temperature. Realizing a spin–phonon coupling (three times higher than for other multiferroic compounds) interface and modulating it in a one-dimensional system have potential benefit when designing effective molecular qubits.