Phonon anomalies and phonon-spin coupling in oriented PbFe0.5Nb0.5O3 thin films
Phonon anomalies and phonon-spin coupling in oriented PbFe0.5Nb0.5O3 thin films
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DOI：
10.1103/physrevb.83.014302
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发表时间：
2011-01-18
影响因子：
3.7
通讯作者：
Scott, J. F.
中科院分区：
文献类型：
--
作者：
Correa, Margarita;Kumar, Ashok;Scott, J. F.
我们目前的拉曼数据的单晶和薄膜样品的多铁性PbFe 0.5Nb 0.5O3（PFN）。我们首先表明，拉曼线的数量和选择规则是兼容的面心立方的Fm-3 m结构，如已知的其他ABO（3）弛豫，如PbSc 1/2 Ta 1/2 O3。然后，我们比较拉曼数据与磁相变温度（TN），扩散铁电相变温度（Tm）和赝结构相变温度（伯恩斯温度类似于T-B）附近的磁化强度和介电常数的异常。PFN薄膜的拉曼光谱的温度演化显示出声子位置、强度和半峰全宽在200、410和650 K温度附近的可测量变化，这些变化分别与实验观察到的T-N、T-m和T-B很好地匹配。最低能量F-2g声子模式的频率随着温度的升高而增加，这是特别出乎意料的。这些变化表明在T-B附近晶体结构从有序相转变为无序相。拉曼研究表明，在T-m和T-N附近存在声子异常，这分别归因于极性纳米区的动力学行为和自旋-声子耦合的弛豫性质和多铁性性质，这与PFN薄膜的介电和磁性质有关.在T-N附近观察到Fe-O模的软化。我们将Fe-O模频率的反常移动与磁化强度的归一化平方联系起来，与实验结果一致表明，由于声子对超交换积分的调制，在T-N附近存在强的自旋-声子耦合，然而，频率随温度的移动很小（
We present Raman data on both single-crystal and thin-film samples of the multiferroic PbFe0.5Nb0.5O3 (PFN). We show first that the number and selection rules of Raman lines are compatible with a face-centered-cubic Fm-3m structure, as is known in other ABO(3) relaxors, such as PbSc1/2Ta1/2O3. We then compare Raman data with anomalies in magnetization and the dielectric constant near the magnetic-phase-transition temperature (T-N), the diffuse ferroelectric-phase-transition temperature (T-m), and the pseudostructural-phase transition temperature (Burns temperature similar to T-B). The temperature evolution of the Raman spectra for the PFN film shows measurable changes in phonon positions, intensities, and full width at half maxima near 200, 410, and 650 K-temperatures that match well with experimentally observed T-N, T-m, and T-B, respectively. The increase in frequency with increasing temperature for the lowest-energy F-2g phonon mode is particularly unexpected. These changes suggest the transition of the crystal structure from an ordered phase to a disordered phase near T-B. The Raman study revealed phonon anomalies in the vicinity of T-m and T-N that are attributed to the dynamical behavior of polar nanoregions and spin-phonon coupling owing to its relaxor and multiferroic nature, respectively, which is well supported by dielectric and magnetic properties of the PFN thin film. Softening of the Fe-O mode was observed near the T-N. We correlate the anomalous shift of the Fe-O mode frequency with the normalized square of the magnetization sublattice; agreement with the experimental results suggests strong spin-phonon coupling near T-N owing to phonon modulation of the superexchange integral; however, the shifts in frequency with temperature are small (