K C Patel R&D Center, Charotar University of Science & Technology, Changa 388 421, Dist. Anand, India.
J Magn Reson. 2012 Dec;225:46-51. doi: 10.1016/j.jmr.2012.10.001. Epub 2012 Oct 17.
The electron spin resonance (ESR) technique has been applied to study the spin dynamics in broad temperature range for rare earth doped Mn(0.5)Zn(0.5)Fe(1.9)Gd(0.1)O(4) (MZG5) magnetic fluid. Zero field cooled (ZFC) ESR spectra of MZG5 fluid exhibit an isotropic shift in the resonance field below 40 K, while the field cooled (FC) ESR spectra show a deviation from sin(2)θ behavior and an angle dependent hysteresis, this unambiguously points to the dominating unidirectional freezing of surface spins below 40 K. Above 60 K, the resonance field exhibits sin(2)θ behavior, indicating the uniaxial anisotropy contribution of core spin. This indicates that surface spin freezing temperature is around 40 K. The presence of surface spin freezing and the coupling between core and surface spins are further supported by cycle dependent FC ESR spectra measured at 20 K, which show the systematic increase in resonance field (H(res)) and intensity. The double peak behavior of blocking temperature distribution retrieved from ZFC-FC magnetization measurement is an additional corroboration of the existence of surface spin glass like layer.
电子自旋共振（ESR）技术已被应用于研究掺杂稀土的 Mn(0.5)Zn(0.5)Fe(1.9)Gd(0.1)O(4)（MZG5）磁性液体在很宽温度范围内的自旋动力学。MZG5 流体的零场冷却（ZFC）ESR 谱在 40 K 以下表现出共振场的各向同性位移，而场冷却（FC）ESR 谱表现出偏离 sin(2)θ行为和角度相关的磁滞，这明确指向表面自旋在 40 K 以下的主导单向冻结。在 60 K 以上，共振场表现出 sin(2)θ行为，表明核自旋的单轴各向异性贡献。这表明表面自旋冻结温度约为 40 K。表面自旋冻结的存在和核自旋与表面自旋之间的耦合进一步得到了在 20 K 下测量的循环相关 FC ESR 谱的支持，该谱显示共振场（H(res)）和强度的系统增加。从 ZFC-FC 磁化测量中获得的阻塞温度分布的双峰行为是表面自旋玻璃层存在的另一个佐证。
