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首页> 外文期刊>Journal of magnetic resonance >Dephasing Relaxation of the Electron Spin Echo of the Vibronic Cu(H_2O)_6 Complexes in Tutton Salt Crystals at Low Temperatures
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Dephasing Relaxation of the Electron Spin Echo of the Vibronic Cu(H_2O)_6 Complexes in Tutton Salt Crystals at Low Temperatures

机译：低温下塔顿盐晶体中振动型Cu（H_2O）_6络合物的电子自旋回波的相移弛豫

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摘要

Two-pulse electron spin echo (ESE) measurements of the phase relaxation (phase memory time T_M) were performed in a series of Tutton salt crystals M_2~IM~(II)(SO_4)_2·6X_2O (M~I = NH_4, K, Cs; M~(II) = Z_n, Mg; X = H, D) weakly doped with Cu~(2+) ions (c ≈ 10~(18) ions/cm~3) in temperature range 4-60 K where ESE signals were detectable. The ESE decay was strongly modulated with proton (or deuteron) frequencies and described by the decay function V(2τ) = V_0 exp (-bτ - mτ~2) with the mτ~2 term being temperature independent and negligible above 20 K. Various mechanisms leading to the τ - or τ~2-type ESE decay are reviewed. The m and b coefficients for nuclear spectral diffusion (NSD), electron spectral diffusion (SD), and instantaneous diffusion (ID) were calculated in terms of existing theories and the resulting rigid lattice T_M~0 times were found to be close one to another within the crystal family with average values: 17.5 μs (NSD protons), 200 μs (NSD deuterons), 8 μs (SD), and 5 μs (ID). The ID dominates but the calculated effective T_M~0 is longer than the experimental T_M~0 = 2 μs. This is due to a nonuniform distribution of the Cu~(2+) ions with a various degree of the disorder in the studied crystals. The acceleration of the dephasing rate 1/T_M with temperature is due to the mechanisms producing exp(-bτ) decay. They are reviewed and two of them were found to be operative in Tutton salt crystals: (a) Excitations to the vibronic levels of energy △ leading to the temperature dependence 1/T_M = B exp(-△/kT), with the vibronic levels produced by strong Jahn-Teller effect, and (b) spin-lattice relaxation processes being effective above 50 K. Based on the △ values being on the order of 100 cm~(-1), the scheme of vibronic levels in the Tutton salts is presented, and the independence of the △ on temperature proves that the adiabatic potential surface shape of Jahn-Teller active Cu(H_2O)_6 complexes is not affected by temperature below 65 K.
机译：在一系列塔顿盐晶体M_2〜IM〜（II）（SO_4）_2·6X_2O（M〜I = NH_4，K）中进行了相变弛豫（相存储时间T_M）的两脉冲电子自旋回波（ESE）测量。 ，Cs; M〜（II）= Z_n，Mg; X = H，D）在4-60 K的温度范围内弱掺杂Cu〜（2+）离子（c≈10〜（18）离子/ cm〜3）在哪里可以检测到ESE信号。 ESE衰减以质子（或氘核）频率强烈调制，并由衰减函数V（2τ）= V_0 exp（-bτ-mτ〜2）描述，其中mτ〜2项与温度无关，在20 K以上可以忽略不计。综述了导致τ-或τ〜2型ESE衰减的机理。根据现有理论计算核谱扩散（NSD），电子谱扩散（SD）和瞬时扩散（ID）的m和b系数，发现所得刚性晶格T_M〜0倍彼此接近在晶体家族中的平均值为17.5μs（NSD质子），200μs（NSD氘核），8μs（SD）和5μs（ID）。 ID占主导地位，但计算出的有效T_M〜0比实验T_M〜0 = 2μs长。这是由于研究的晶体中具有各种程度的无序的Cu〜（2+）离子的不均匀分布所致。相移速率1 / T_M随温度的加速是由于产生exp（-bτ）衰减的机制引起的。对它们进行了审查，发现其中两个可在塔顿盐晶体中起作用：（a）激振了能量△的振动子能级△，导致温度依赖性1 / T_M = B exp（-△/ kT），且振动子能级由强Jahn-Teller效应产生，（b）自旋晶格弛豫过程在50 K以上有效。基于△值在100 cm〜（-1）数量级，图顿盐中的电子能级方案给出了△在温度上的独立性，证明了Jahn-Teller活性Cu（H_2O）_6配合物的绝热势面形状不受65 K以下温度的影响。

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