Fe $^{3+}$低能级取代对TbMnO $_3$中磁电耦合的影响
Modifying the magnetoelectric coupling in TbMnO$_3$ by low-level Fe$^{3+}$ substitution
摘要：
本文报道了Fe $^{3+}$对TbMn $_{1-x}$ Fe $_x$ O $_3$（$x=0$，0.02和0.04）中的静态和动态磁电耦合的影响。阳离子取代对竞争性磁相互作用之间的平衡有很大的影响，因此，在低温下对磁性结构和铁电相的稳定性有很大的影响。低位的电磁振子激发激活TbMnO $_3$中的摆线调制的反铁磁和铁电相，而它被观察到TN的Fe取代的化合物，静态和动态磁电耦合的不同机制。第二个电活性激发近40厘米$^{-1}$解释通过Tb 3+晶体场效应。这种激发被观察到室温，并表现出显着的15厘米$^{-1}$降频冷却Fe取代的化合物。电磁振子和晶体场激发被发现耦合到极性声子的频率高达250厘米$^{-1}$。拉曼光谱显示纯TbMn O $_3$在TN以下存在自旋-声子耦合，但TbMn $_{0.96}$ Fe $_{0.04}$ O $_3$的自旋-声子耦合开始温度随Fe浓度的增加而升高，达到100 K。自旋-声子耦合和晶体场激发，耦合到氧运动的T-依赖性的磁化率TN以上的异常占。
英文摘要：
We report a comprehensive study of the low-level substitution of Mn$^{3+}$ by Fe$^{3+}$ effect on the static and dynamic magnetoelectric coupling in TbMn$_{1-x}$Fe$_x$O$_3$ ($x=0$, 0.02 and 0.04). The cationic substitution has a large impact on the balance between competitive magnetic interactions and, as a result, on the stabilization of the magnetic structures and ferroelectric phase at low temperatures. Low-lying electromagnon excitation is activated in the cycloidal modulated antiferromagnetic and ferroelectric phase in TbMnO$_3$, while it is observed up to TN in the Fe-substituted compounds, pointing for different mechanisms for static and dynamic magnetoelectric coupling. A second electrically active excitation near 40 cm$^{-1}$ is explained by means of Tb3+ crystal-field effects. This excitation is observed up to room temperature, and exhibits a remarkable 15 cm$^{-1}$ downshift on cooling in Fe-substituted compounds. Both electromagnon and crystal-field excitations are found to be coupled to the polar phonons with frequencies up to 250 cm$^{-1}$. Raman spectroscopy reveals a spin-phonon coupling below TN in pure TbMnO$_3$, but the temperature where the coupling start to be relevant increases with Fe concentration and reaches 100 K in TbMn$_{0.96}$Fe$_{0.04}$O$_3$. The anomalies in the T-dependence of magnetic susceptibility above TN are well accounted by spin-phonon coupling and crystal-field excitation, coupled to oxygen motions.
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