A Nonequilibrium Atomic‐Scale Simulation for Time‐Evolutional Spin Dynamics of a Radical Bridged Trinuclear Ni(II) Complex

A nonequilibrium atomic‐scale simulation for time‐evolutional spin dynamics on molecular magnets is important to develop quantum electronic devices based on spin clusters and single molecule magnets. Spin dynamic calculations of individual spins in a radical‐bridged trinuclear Ni(II) complex are presented using the stochastic Landau–Lifshitz–Gilbert model. The model involving superexchange interactions ( J ij ) of spins between Ni ( S = 1) cations (Ni1, Ni2, Ni3) and a hexahydroxytriphenylene (HHTP) radical ( S = 1/2), and single‐ion magnetic anisotropy ( D i ) of Ni. The time‐evolution simulation reveals that the spin directions show a damping oscillation within ≈10 ps. At equilibrium, the spins are almost in the aromatic HHTP radical plane ( xy ‐plane). The angles of the spins on Ni1, Ni2, Ni3, and the radical relative to the x ‐axis are 23.6°, 86.0°, 30.1°, and 31.4°, respectively, mainly due to the negative D Ni1 value. The oscillation frequencies of 120 GHz and 210 GHz correspond to the zero‐field magnetic resonance. Temperature‐evolution simulations reveal that the directions of the spins gradually fluctuate with increasing temperature, and finally, the spins are almost randomly oriented above 5 K, reflecting the energy barrier of the total magnetic anisotropy. Such nonequilibrium atomic‐scale simulations of time‐ and temperature‐evolution dynamics would be useful for predicting the qubit or coherence state of single molecule magnets.