arXiv subjects

Itsuki Shimamura

Publications and source records attributed to Itsuki Shimamura.

3 recordsLinked to original sources

arXiv2026

Realization of a triangular spin necklace in a verdazyl-based Ni complex

We successfully synthesized a verdazyl-based complex, ($m$-Py-V)$_3$[Ni(NO$_3$)$_2$], in which Ni$^{2+}$ ions and verdazyl radicals form a one-dimensional, triangular spin necklace consisting of spin-1/2 and spin-1 units. Molecular orbital calculations reveal strong antiferromagnetic (AF) interactions between inversion-related radical pairs that form spin-1/2 singlet dimers. The remaining verdazyl and Ni$^{2+}$ spins form frustrated triangular units, creating a distinctive spin network. Magnetic susceptibility and specific heat measurements identify a phase transition to an AF order. The application of magnetic fields suppresses the phase transition signal, suggesting field-induced decoupling of the spin-1 moments. Electron spin resonance measurements are used to evaluate the easy-axis anisotropy of spin-1, which may promote the AF order. This work provides a rare example of a geometrically frustrated quantum spin chain realized via molecular design, thereby offering a platform for exploring frustration-driven quantum phases in low-dimensional materials.

cond-mat.str-el↗

arXiv2025

Experimental benchmark of the quantum-classical crossover in a spin ladder

We report a spin-(1/2, 5/2) three-leg ladder realized in a radical-Mn polymer, exhibiting an antiferromagnetic transition and magnetization curves accurately described by classical mean-field theory. Although the underlying spin model intrinsically supports strong quantum fluctuations, as confirmed by quantum Monte Carlo simulations, the real system shows an anomalously complete suppression of quantum behavior. These findings provide a key experimental benchmark for the quantum-classical crossover and suggest that lattice topology can play a crucial role in tuning the balance between quantum and classical physics in strongly correlated systems.

cond-mat.str-el↗

arXiv2025

Gapless behavior in a two-leg spin ladder with bond randomness

We successfully synthesized [Cu$_2$(AcO)$_4$($p$-Py-V-$p$-F)$_2$]$\cdot$4CHCl$_3$, a verdazyl-based complex with a paddlewheel structure comprising two Cu atoms, which induces strong antiferromagnetic (AF) exchange interactions between Cu spins, generating a nonmagnetic singlet state at low temperatures. Two primary exchange interactions between radical spins generate a spin-1/2 AF two-leg ladder. In addition, two possible positional configurations of the F atom in the complex create four different overlap patterns of molecular orbitals, introducing bond randomness in the spin ladder. The observed experimental behaviors, such as the Curie tail in the magnetic susceptibility and the gapless gradual increase in the magnetization curve, are attributed to a broad distribution of excitation energies and a few orphan spins in the random-singlet (RS) state that are stabilized by bond randomness. The low-temperature specific heat exhibits a temperature dependence with $\propto 1/|{\rm{ln}}T|^3$, demonstrating the formation of the RS state in unfrustrated systems. We also consider the effect of restricted patterns of exchange interactions and one-dimensional nature of the system on the RS state.

cond-mat.str-el↗