Strong spin–phonon coupling in Gd-filled nanotubes

Abstract

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 (ωGext+andωGint+) 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 Gext+ and Gint+ phonon modes, respectively, analyzed by comparing the phonon frequency variation (Δω) 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.

Carbon Nanotube Devices for Quantum Technology

“…In another study, Gd 3+ ions were used to fill double-wall CNTs (DWCNTs) and spin-phonon coupling was investigated with low-temperature Raman spectroscopy. The spin-phonon coupling strength was shown to be about three times higher than that for other multiferroic compounds [102]. Mechanically interlocked Cu 2+ and Co 2+ metalloporphyrin dimer rings around a SWCNT, or a mechanically interlocked nanotube (MINT), have also been demonstrated, as shown in the transmission electron microscope (TEM) image in Figure 6a.…”

“…While single spins can serve as qubits, coupling to mechanical motion of CNTs can enable detection and manipulation of spin qubits [101]. To achieve strong coupling between spins and phonons, CNTs can be either functionalized with magnetic ions [102] or molecules [103], or interfaced with solid-state qubits such as NV centers in diamond [104].…”

Observation of High Magnetic Bistability in Lanthanide (Ln = Gd, Tb and Dy)-Grafted Carbon Nanotube Hybrid Molecular System

“…The origin of such large magnetic anisotropies can be traced back to the exchange interactions between the metal ion and the π-electronic systems of the MWCNTs. The local spins (molecular magnets) with a proximity to the itinerant conduction electrons of the nanotubes develop either a ferromagnetic or an anti-ferromagnetic ordering through a variety of exchange interactions including Coulomb, spin-exchange [33] and weak intra-or inter-molecular interactions [40]. Further, competition between these interactions is mediated by the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction.…”

“…In 2018, we reported the Kondo effect with enhanced magnetic properties in a Gd-MWCNT system [25], and thereafter demonstrated how the magnetic properties could be tuned by the careful chemical functionalization of MWCNTs [32]. Later, we showed how spin relax through interaction (spin-phonon coupling) with the discrete phonon spectrum of CNTs [33]. Herein, we report the magnetic anisotropy and magnetization dynamics observed by replacing the central ion in the Ln-EDTA (Ln = Gd III , 1; Tb III , 2 and Dy III , 3)-grafted MWCNT molecular system.…”