NMR as a Probe of the Relaxation of the Magnetization in Magnetic Molecules

摘要: We investigate the time autocorrelation of molecular magnetization M(t) for three classes magnetic molecules (antiferromagnetic rings, grids and nanomagnets), in contact with phonon heat bath. For all classes, we find that exponential decay fluctuations M(t), associated irreversible exchange energy bath, is characterized by a single characteristic �(T,B) not too high temperature T field B. This reflected nearly single-lorentzian shape spectral density fluctuations. show such are effectively probed NMR, our theory explains recent phenomenological observation Baek et al. (PRB70, 134434) Larmor-frequency dependence 1/T1 data large number AFM rings fits to form. A central aspect physics way observables, particularly M, affected interactions spins other degrees freedom. When latter behave as they cause decoherence evolution usually leading relaxation dynamics time-decay equilibrium The understanding characterization mechanisms crystals containing only important evident fundamental reasons, but also because and, more generally, decoherence, constitute major obstacle envisaged technological applications these molecules. In particular, M through phonons sets an upper bound[1] range which nanomagnets could be used classical bits memory. possible application some elementary units (qubits) quantum information processing (QIP)[2], dissipation from qubits nuclear-spins bath main concern regarding efficiency logical gates performance computation. this work, (AFM) due spin-phonon dominated τ(T, B) over wide temperatures applied fields. While was already known long-time nanomagnets, results applies completely different molecules, holds on much shorter time-scales well. Indeed, considered (T, regimes frequency λ0 = 1/τ dominates spectrum extent even experimental probes whose intrinsic very will nevertheless detect mostly contribution. NMR measurements longitudinal nuclear rate can direct probe fully consistent picture. instance, explain [3] lorentzian form, elucidate meaning behavior lorentzian. addition, collected new Mn3x3 grid give further support At last, reanalyzed prototype nanomagnet Fe8. Each molecule described spin Hamiltonian