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首页> 外文期刊>Solid State Communications >Spin-echo EPR spin-probe measurement of the microsecond-range magnetic field fluctuations near the surface of crystals of the nanomagnet Mn_(12)-Ac
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Spin-echo EPR spin-probe measurement of the microsecond-range magnetic field fluctuations near the surface of crystals of the nanomagnet Mn_(12)-Ac

机译：纳米磁铁Mn_（12）-Ac晶体表面附近微秒范围磁场起伏的自旋回波EPR自旋探针测量

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摘要

Electron spin-echo detected EPR (ED-EPR) at the X-band, using the spin probe N-methylphenazinium-tetracyanoquino-dimethane (NMP-TCNQ), enabled us to detect fluctuations of the local magnetic field close to the surface of a single crystal of [Mn_(12)O_(12)(CH_3COO)_(16)(H_2O)_4]·2CH_3COOH·4H_2O (Mn_(12)-Ac) in its superparamagnetic regime. The ED-EPR signal from NMP-TCNQ is unexpectedly broad in comparison to standard sharp and intense spectrum detected by continuous wave EPR (CW-EPR). This broadened peak represents inhomogeneous broadening, whose homogenous component line width, δ, was related to its phase memory time T_M as δ ～ 1/T_M ～ 1/T_2; T_M was found to be in the microsecond range around 15 K. The temperature dependence of T_M follows that of the bulk magnetization fluctuations. The Arrhenius activation energy for these probe detected fluctuations is ～45 K, which is distinctly lower than that (～60 K) for the bulk magnetization reversal for Mn_(12)-Ac, implicating a significant role for surface effects.
机译：电子自旋回波使用自旋探针N-甲基吩嗪鎓-四氰基喹啉-二甲烷（NMP-TCNQ）在X波段检测到EPR（ED-EPR），使我们能够检测到靠近表面的局部磁场的波动。 [Mn_（12）O_（12）（CH_3COO）_（16）（H_2O）_4]·2CH_3COOH·4H_2O（Mn_（12）-Ac）的单晶处于超顺磁态。与通过连续波EPR（CW-EPR）检测到的标准清晰锐利光谱相比，来自NMP-TCNQ的ED-EPR信号出乎意料地宽。这个加宽的峰代表不均匀的加宽，其均匀的成分线宽度δ与它的相存储时间T_M相关，为δ〜1 / T_M〜1 / T_2。发现T_M在15 K附近的微秒范围内。T_M的温度依赖性遵循整体磁化涨落的温度依赖性。这些探头检测到的波动的阿累尼乌斯活化能为〜45 K，明显低于Mn_（12）-Ac的整体磁化反转的（-60 K），这暗示了表面效应的重要作用。

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