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Equilateral spin triangles have long been a topic of interest in quantum magnetism, offering a fertile ground to explore phenomena such as frustration [1], spin-electric coupling [2], and multiferroic ordering [3]. Despite substantial progress, realizing ideal triangular spin networks remains a challenge, often hindered by structural distortions. The organic compound TNN·CH₃CN overcomes these limitations with its isotropic organic radical spins, free from Jahn-Teller effects, allowing uniform exchange interactions. This makes TNN·CH₃CN an ideal candidate for investigating the novel multiferroic phases predicted by Kamiya and Batista [3].
In this work, we focus on the 1/3 magnetization plateau (1.25 < B < 8.49 T), where TNN·CH₃CN exhibits a twofold-degenerate S=1/2, Sz=1/2 ground state [4]. This intriguing phase exhibits ferroelectric order below 0.35 K without a conventional spin-ordering transition, offering a unique window into the interplay between spin and electric properties in triangular spin systems. By employing polarized neutron diffraction (PND) and muon spin relaxation (μSR) techniques, we investigate the emergence of collective spin behavior within the plateau [5].
The results align well with theoretical predictions and highlight the trimer formation at low temperatures, where the initially independent paramagnetic spins couple below 5.5 K.
[1] J. F. Nossa and C. M. Canali, Phys. Rev. B, 89, 235435 (2014).
[2] S. Nakatsuji et al., Science, 309, 1697-1700 (2005).
[3] Y. Kamiya and C. D. Batista, Phys. Rev. Lett., 108, 097202 (2012).
[4] C. P. Aoyama, PhD thesis, University of Florida (2015).
[5] M. Pardo-Sainz, PhD thesis, University of Zaragoza (2024).
