Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2
Spin dynamics of paramagnetic centers with anisotropic g tensor and spin of 1/2
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DOI：
10.1016/j.jmr.2012.05.011
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发表时间：
2012-08-01
影响因子：
2.2
通讯作者：
Bowman, Michael K.
中科院分区：
文献类型：
--
作者：
Maryasov, Alexander G.;Bowman, Michael K.
研究了g张量各向异性对具有真实的或有效自旋为1/2的顺磁中心自旋动力学的影响。g各向异性影响EPR信号的激发和检测，产生常规连续波（CW）EPR和脉冲EPR谱之间的显着差异。自旋和磁矩矢量的大小和方向通常彼此不成比例，但通过g张量彼此相关。由于g各向异性，平衡磁矩方向通常既不平行于磁场也不平行于自旋量子化轴。在用短微波脉冲激发之后，自旋矢量在通常不垂直于所施加的磁场的平面中围绕其量子化轴进动。巧合的是，磁矩矢量在一个与外部磁场完全垂直的平面内绕其平衡方向进动。在一般情况下，磁矩的振荡部分是椭圆极化的，进动的方向由g张量行列式的符号（g张量签名）决定。传统的脉冲和cw EPR谱仪不允许确定的g张量签名或磁矩轨迹的椭圆率。当g张量各向异性显著时，通常不可能为无取向或“粉末”样品中的简单脉冲设置均匀的自旋转向角。(C)2012 Elsevier Inc. All rights reserved.
The influence of g tensor anisotropy on spin dynamics of paramagnetic centers having real or effective spin of 1/2 is studied. The g anisotropy affects both the excitation and the detection of EPR signals, producing noticeable differences between conventional continuous-wave (cw) EPR and pulsed EPR spectra. The magnitudes and directions of the spin and magnetic moment vectors are generally not proportional to each other, but are related to each other through the g tensor. The equilibrium magnetic moment direction is generally parallel to neither the magnetic field nor the spin quantization axis due to the g anisotropy. After excitation with short microwave pulses, the spin vector precesses around its quantization axis, in a plane that is generally not perpendicular to the applied magnetic field. Paradoxically, the magnetic moment vector precesses around its equilibrium direction in a plane exactly perpendicular to the external magnetic field. In the general case, the oscillating part of the magnetic moment is elliptically polarized and the direction of precession is determined by the sign of the g tensor determinant (g tensor signature). Conventional pulsed and cw EPR spectrometers do not allow determination of the g tensor signature or the ellipticity of the magnetic moment trajectory. It is generally impossible to set a uniform spin turning angle for simple pulses in an unoriented or 'powder' sample when g tensor anisotropy is significant. (C) 2012 Elsevier Inc. All rights reserved.