Coherent spin rotation in the presence of a phonon-bottleneck effectL. Chen and I. Chiorescu
Physics Department and the National High Magnetic Field Laboratory, Florida State University 1800 E. Paul Dirac Drive, Tallahassee, FL 32310, USA
received 28 May 2009; accepted in final form 28 August 2009; published September 2009
published online 23 September 2009
A characteristic of spin reversal in the presence of phonon bottleneck is the deviation of the magnetization cycle from a reversible function into an opened hysteresis cycle. In recent experiments on molecular magnets (e.g. and ), the zero-field level repulsion was sufficiently large to ensure an otherwise adiabatic passage through zero-field and the magnetization curves can be described by using only a phonon-bottleneck model. Here, we generalize the phonon-bottleneck model into a model able to blend the non-adiabatic dynamics of spins with the presence of a non-equilibrium phonon bath. In this simple phenomenological model, Bloch equations are written in the eigenbasis of the effective spin Hamiltonian, considered to be a two-level system at low temperatures. The relaxation term is given by the phonon-bottleneck mechanism. To the expense of calculus time, the method can be generalized to multi-level systems, where the notion of Bloch sphere does not apply but the density matrix formalism is still applicable.
75.45.+j - Macroscopic quantum phenomena in magnetic systems.
75.50.Xx - Molecular magnets.
75.10.Jm - Quantized spin models.
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