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首页> 外文期刊>Journal of Physics. Condensed Matter >Dynamical properties and instability of local fluorite BaF2 structure around doped Mn2+ ions - EPR and electron spin echo studies
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Dynamical properties and instability of local fluorite BaF2 structure around doped Mn2+ ions - EPR and electron spin echo studies

机译：掺杂的Mn2 +离子周围局部萤石BaF2结构的动力学性质和不稳定性-EPR和电子自旋回波研究

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摘要

The electron paramagnetic resonance (EPR) and electron spin echo (ESE) were measured at the X-band for Mn2+ in a BaF2 crystal in the temperature range 4.2-300 K. In addition to the cubic symmetry centre, two other lower concentration tetragonal centres were identified. Temperature variations and computer simulation of the EPR spectrum confirm that the cubic symmetry of the MnF8 centre is deformed to two T-d tetrahedra of different dimensions at around 45 K. Electron spin relaxation was measured in the temperature range 4.2-35 K, where the ESE signal was detectable. For higher temperature the Mn2+ dynamics produces homogeneously broadened EPR lines. At the lowest temperatures the spin-lattice relaxation is governed by ordinary phonon processes with 1/T-1 similar to T-5. The efficiency of these processes rapidly decreases and at about 11 K a local mode of energy 17 cm(-1) becomes the relaxation mechanism. Phase relaxation observed as ESE signal dephasing indicates that after the local deformation jumps (tunnelling with frequency 4 x 10(8) s(-1)) between the two tetrahedral configurations appear, with the energy barrier being the local mode energy. This motion is directly visible as a resonance-type enhancement of the ESE dephasing rate 1/T-M around 11 K. Only the cubic centre displays the above dynamics.
机译：在4.2-300 K的温度范围内，在BaF2晶体中Mn2 +的X谱带上测量了电子顺磁共振（EPR）和电子自旋回波（ESE）。除立方对称中心外，还有两个较低浓度的四方中心被确定。温度变化和EPR谱的计算机模拟证实，MnF8中心的立方对称性在45 K左右变形为两个不同尺寸的Td四面体。在4.2-35 K的温度范围内测量了电子自旋弛豫，其中ESE信号被检测到。对于更高的温度，Mn2 +动力学会产生均匀加宽的EPR线。在最低温度下，自旋晶格弛豫由1 / T-1的普通声子过程控制，类似于T-5。这些过程的效率迅速降低，并且在大约11 K时，局部能量模式17 cm（-1）成为松弛机制。在ESE信号移相时观察到的相弛豫表明，在两个四面体配置之间出现局部形变跳跃（以频率4 x 10（8）s（-1）敲击）后，能量屏障为局部模式能量。该运动作为ESE相移速率1 / T-M在11 K附近的共振型增强而直接可见。只有立方中心显示了上述动态。

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