The rapid development of big data and quantum technology has created an urgent demand for high-density information storage and quantum carriers. However, as microelectronic devices approach the atomic scale, traditional bulk magnetic materials are inevitably constrained by the physical barrier of the "superparamagnetic effect," leading to the loss of magnetic memory. In this context, single-molecule magnets (SMMs), precisely constructed using coordination chemistry, have successfully broken through traditional magnetic limits due to their slow magnetic relaxation and magnetic hysteresis at the single-molecule level. Building upon this, if single-molecule magnets can further act as a sensory bridge between magnetic fields and strain, they can broaden the application of such materials in other fields through magnetoelastic coupling. Recently, Professor Zheng Yanzhen's team discovered a single-molecule magnetic ring whose shape responds to changes in the magnetic field during their research on single-molecule magnets, naming it a single-molecule magnetostrictor.
Traditionally, magnetostriction phenomena originate primarily from magnetic domain inversion or changes in the magnetic anisotropy axis. The latter can be generated by paramagnetic materials and can also be observed in molecular magnets; however, magnetostriction induced by magnetic exchange coupling interactions has not yet been demonstrated. Because the {Fe 8 Gd 8 } molecule crystallizes in a cubic space group and both Fe(III) and Gd(III) possess half-filled magnetic orbitals, the contribution of magnetic anisotropy to the magnetostrictive effect of this crystal is extremely limited. To accurately isolate the core Fe 3+ -Gd 3+ magnetic exchange coupling from the complex spin system, the research team introduced isostructural substitution models containing diamagnetic ions ({Fe 8 Y 8 } and {Sc 8 Gd 8 }) for "background subtraction". Facing a Hilbert space of up to 10 13 , the team employed Quantum Monte Carlo (QMC) simulations based on the Stochastic Series Expansion (SSE) method. Using High-Frequency/High-Field Electron Paramagnetic Resonance (HF-EPR) spectroscopy, the team determined that the g -value of the {Fe 8 Gd 8 } molecule is 2.03, confirming that the single-ion anisotropy is negligible. Meanwhile, in low-temperature (0.2 K to 10 K) heat capacity measurements, the system did not exhibit any λ-type specific heat anomalies indicative of long-range magnetic ordering. This rules out the two magnetostriction mechanisms typically found in traditional materials: "magnetic domain rearrangement" and "single-ion anisotropy". Utilizing a high-resolution capacitive dilatometer under conditions of 2K and a 7T magnetic field, the saturation magnetostriction ( λ s ) of {Fe 8 Gd 8 } reached 50 ppm, a value comparable to that of classic industrial-grade polycrystalline iron and polycrystalline nickel metals. Subsequently, the team combined QMC simulations with the mean-field approximation, achieving a perfect alignment between theoretical calculations and experimental strain data. This work demonstrates that the pronounced low-temperature magnetostriction effect observed in the {Fe 8 Gd 8 } crystal is driven by the intramolecular ferromagnetic coupling between Fe(III) and Gd(III). The resulting large spin ground state exhibits a rapid response to the applied magnetic field, inducing macroscopic crystal striction—a phenomenon characterizing what can be termed a 'single-molecule magnetostrictor'.
This research achievement, titled "Single-molecule magnetostrictor: an {Fe 8 Gd 8 } cubic crystal exhibits temperature-dependent magnetostriction," was published online in the National Science Review . Doctoral student Li Dongyang and Researcher Qin Lei from Xi'an Jiaotong University are the co-first authors. The corresponding authors are Professor Zheng Yanzhen and Assistant Professor Zhai Yuanqi from Xi'an Jiaotong University, as well as Researcher Fu Zhendong from the Songshan Lake Materials Laboratory. This work was supported by the National Natural Science Foundation of China and other related funds.
National Science Review
Experimental study