Taukulis R, Cēbers A
University of Latvia, Zeļļu-8, Rīga LV-1002, Latvia.
Phys Rev E Stat Nonlin Soft Matter Phys. 2012 Dec;86(6 Pt 1):061405. doi: 10.1103/PhysRevE.86.061405. Epub 2012 Dec 14.
An algorithm is developed for numerical simulation of coupled stochastic dynamics of magnetic moment and magnetic anisotropy axis of a nanoparticle. Time-correlation functions of the magnetic moment and its components longitudinal and transverse to the magnetic anisotropy axis are calculated by averaging along the stochastic trajectory. The longitudinal and transverse relaxation times are found by fitting the time correlation functions. Existing theoretical relations derived by the effective field approach in the limit of small fields are confirmed. The time-correlation functions of magnetic moments of nanoparticles in dependence on their properties are calculated numerically for arbitrary large magnetic fields and it is shown that they may be approximated by a sum of several exponentials. These results are applied for the calculation of relaxivity parameters of nuclear magnetic resonance (NMR) imaging in dependence on the field strength.
开发了一种算法，用于对纳米颗粒的磁矩和磁各向异性轴的耦合随机动力学进行数值模拟。通过沿随机轨迹求平均，计算了磁矩及其相对于磁各向异性轴纵向和横向分量的时间关联函数。通过拟合时间关联函数确定纵向和横向弛豫时间。证实了在小场极限下由有效场方法导出的现有理论关系。针对任意大磁场，数值计算了纳米颗粒磁矩的时间关联函数与其性质的依赖关系，结果表明它们可以用几个指数之和来近似。这些结果被应用于计算核磁共振（NMR）成像的弛豫率参数与场强的依赖关系。
