Tuning Magnetic Properties of a Carbon Nanotube-Lanthanide Hybrid Molecular Complex through Controlled Functionalization

Molecular magnets attached to carbon nanotubes (CNT) are being studied as potential candidates for developing spintronic and quantum technologies. However, the functionalization routes used to develop these hybrid systems can drastically affect their respective physiochemical properties. Due to the complexity of this systems, little work has been directed at establishing the correlation between the degree of functionalization and the magnetic character. Here, we demonstrate the chemical functionalization degree associated with molecular magnet loading can be utilized for controlled tuning the magnetic properties of a CNT-lanthanide hybrid complex. CNT functionalization degree was evaluated by interpreting minor Raman phonon modes in relation to the controlled reaction conditions. These findings were exploited in attaching a rare-earth-based molecular magnet (Gd-DTPA) to the CNTs. Inductively coupled plasma mass spectrometry, time-of-flight secondary ion mass spectrometry and super conducting quantum interference device (SQUID) measurements were used to elucidate the variation of magnetic character across the samples. This controlled Gd-DTPA loading on the CNT surface has led to a significant change in the nanotube intrinsic diamagnetism, showing antiferromagnetic coupling with increase in the Weiss temperature with respect to increased loading. This indicates that synthesis of a highly correlated spin system for developing novel spintronic technologies can be realized through a carbon-based hybrid material

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