Spin-lattice relaxation within a dimerized Ising chain in a magnetic field

WOS: 000340710500095
A qualitative study of the spin-lattice relaxation within a dimerized Ising chain in a magnetic field is presented. We have first determined the time dependence of the deviation of the lattice distortion parameter delta Delta from the equilibrium state within framework of a technique combining the statistical equilibrium theory based on the transfer matrix method and the linear theory of irreversible thermodynamics. We have shown that the time dependence of the lattice distortion parameter is characterized by a single time constant (tau) which diverges around the critical point in both dimerized (Delta not equal 0) and uniform (Delta = 0) phase regions. When the temperature and magnetic field are fixed to certain values, the time tau depends only on exchange coupling between the spins. It is a characteristic time associated with the long wavelength fluctuations of distortion. We have also taken into account the effects of spatial fluctuations on the relaxation time using the full Landau-Ginzburg free energy functional. We have found an explicit expression for the relaxation time as a function of temperature, coupling constant and wave vector (q) and shown that the critical mode corresponds to the case q = 0. Finally, our results are found to be in good qualitative agreement with the results obtained in recent experimental study on synchrotron x-ray scattering and muon spin relaxation in diluted material Cu1-yMgyGeO3 where the composition y is very close to 0.0209. These results can be considered as natural extensions of some previous works on static aspects of the problem. (C) 2014 AIP Publishing LLC.
Scientific Research Projects Coordination Unit of Akdeniz University [2013.05.0115.018]
This work was supported by the Scientific Research Projects Coordination Unit of Akdeniz University, Project No. 2013.05.0115.018. One of the authors (R. E.) thanks to Dr. Jozef Strecka from P.J. Safarik University (Slovak Republic) for useful discussions on the topic at the early stages of this work.