We observed Raman scattering from magnon in frequency range from 10 to 65 cm-1 in BiFeO3 single crystals at cryogenic temperatures; the temperature dependence of the magnon frequency at 18.2 cm-1 approximates an S=5/2 Brillouin function up to the temperature (280 K) at which the magnon becomes overdamped. The diverging cross-section and the frequency-shift at 140K and 200 K implies a magnon-reorientation transition as in orthoferrites. Magnons in polar materials such as BiFeO3 are often termed electromagnons meaning that they possess an electric dipole moment due to magnetoelectric coupling.
Colossal magnon-phonon coupling in multiferroic Eu$_{0.75}$Y$_{0.25}$MnO$_3$
本文报道了Eu $_{0.75}$ Y $_{0.25}$ MnO $_3$的变温远红外光谱（10-250 cm $^{-1}$）的磁诱导电偶极吸收谱。这些光谱只发生在$e||a$极化中，由两个相对窄的电磁子特征和一个宽的吸收带组成，其中电磁子特征在$T_{FE}=30$ K开始，而吸收带在远高于$T_N=47$ K的温度下持续存在。所观察到的激发占步的静态介电常数在铁电相。观测到80 cm $^{-1}$处的电磁振子与附近的最低光学声子强耦合，该声子将其光谱重量的1/2以上转移到磁振子。我们把宽背景吸收的起因归结为声子的两个磁振子发射衰变过程。
Terahertz spectroscopy of electromagnons in Eu_{1-x}Y_xMnO_3
钇掺杂EuMnO $_3$的介电常数谱，在0 =< x =< 0.5 have been investigated in the terahertz frequency range. Magnetoelectric contributions to the permittivity were observed in all compositions for ac electric fields parallel to the crystallographic a-axis. Well defined electromagnons exist for x >= 0.2接近ν~ 20 cm^{-1}的组成范围内，并且随着掺杂，介电强度强烈增加。除了电磁振子，广泛的贡献磁电起源观察到的所有组合物。对于Eu_{0.8} Y_{0.2} MnO_3，由于外加磁场的作用，产生了一个倾斜的反铁磁相，从而抑制了电磁振子。在不同的掺杂制度的磁电效应进行了详细讨论。
Emergence of multiple quasi-ferromagnetic magnon modes induced by strong magnetoelastic coupling in $TmFeO_3$ single crystal
Johannes Gutenberg University Mainz（约翰内斯·古腾堡美因茨大学）；Shanghai University（上海大学）；Shanghai Jiao Tong University（上海交通大学）；Norwegian University of Science and Technology（挪威科技大学）
Magnons and Magnetodielectric Effects in CoCr$_2$O$_4$: Raman Scattering Studies
磁电材料由于其所表现出的丰富的现象而引起了广泛的技术和科学兴趣，包括磁性和铁电性有序的共存，磁介电行为，以及诸如电磁振子的奇异混合激发。多铁性尖晶石材料CoCr $_2$ O $_4$是多铁性材料的一个特别有趣的例子，因为亚铁磁相的磁电行为的证据似乎与传统的非共线自旋驱动机制相冲突。用非弹性光散射方法研究了CoCr $_2$ O $_4$的磁振子和声子谱随温度、压力和磁场的变化.在CoCr $_2$ O $_4$的居里温度（$T_C \sim 94$ K）以下，我们观察到具有T $_{1g}$对称性的$ω\sim 16 \,\text{cm}^{-1}$ $\boldsymbol q=0$磁振子，它具有轴向矢量的变换性质。T $_{1g}$对称磁振子的极大拉曼强度是具有大磁光响应的材料的特征，并且可能由强烈调制CoCr $_2$ O $_4$中的介电响应的大的磁波动引起。的T $_{1g}$ -对称磁振子的拉曼磁化率表现出很强的磁场依赖性，这是一致的磁介电响应中观察到的CoCr $_2$ O $_4$，这表明磁介电行为在CoCr $_2$ O $_4$主要是从磁场依赖性抑制的磁波动，强烈耦合到长波长的声子。随着所施加的压力增加CoCr $_2$ O $_4$中的磁各向异性降低了CoCr $_2$ O $_4$中T $_{1g}$对称性磁振子拉曼磁化率的磁场依赖性，表明应变可用于控制…
We report broadband microwave absorption spectroscopy of the layered antiferromagnet CrCl3. We observe a rich structure of resonances arising from quasi-two-dimensional antiferromagnetic dynamics. Due to the weak interlayer magnetic coupling in this material, we are able to observe both optical and acoustic branches of antiferromagnetic resonance in the GHz frequency range and a symmetry-protected crossing between them. By breaking rotational symmetry, we further show that strong magnon-magnon coupling with large tunable gaps can be induced between the two resonant modes.
We study theoretically the influence of the temperature and disorder on the spin wave spectrum of the magnonic crystal Fe$_{1-c}$Co$_{c}$. Our formalism is based on the analysis of a Heisenberg Hamiltonian by means of the wave vector and frequency dependent transverse magnetic susceptibility. The exchange integrals entering the model are obtained from the \emph{ab initio} magnetic force theorem. The coherent potential approximation is employed to treat the disorder and random phase approximation in order to account for the softening of the magnon spectrum at finite temperatures. The alloy turn…
Thermoelectric modules are a promising approach to energy harvesting and efficient cooling. In addition to the longitudinal Seebeck effect, recently transverse devices utilizing the anomalous Nernst effect (ANE) have attracted interest. For high conversion efficiency, it is required that the material should have a large ANE thermoelectric power and low electrical resistance, the product of which is the ANE conductivity. ANE is usually explained in terms of intrinsic contributions from Berry curvature. Our observations suggest that extrinsic contributions also matter. Studying single-crystal Mn…
Hybrid systems combining magnons and superconducting quantum circuits have attracted increasing interest in recent years. Magnonic crystals (MCs) are one of the building blocks of room-temperature magnonics and can be used to create devices with an engineered band structure. These devices, exhibiting tunable frequency selectivity and the ability to store travelling excitations in the microwave regime, may form the basis of a set of new tools to be used in the context of quantum information processing. In order to ascertain the feasibility of such plans, MCs must be demonstrated to work at the …
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 compoun…
Weak coupling of pseudoacoustic phonons and magnon dynamics in incommensurate spin ladder compound Sr14Cu24O41
有趣的晶格动力学已被预测为包含无公度子结构的非周期晶体。在这里，我们报告的非弹性中子散射测量的声子和磁振子的色散在Sr 14 Cu 24 O 41，其中包含无公度的一维（1D）链和二维（2D）的梯形子结构。两个不同的赝声学声子模式，对应于一个子晶格对其他的滑动运动，观察沿非公度轴极化的原子运动。在长波长范围内，滑动模的能隙非常小，仅为1.7-1.9 meV，表明两个无公度子晶格之间存在弱相互作用.测量还揭示了阶梯子晶格的带隙和陡峭的线性磁振子色散。该磁振子支的高群速度以及与声学和赝声学声子的弱耦合可以解释Sr 14 Cu 24 O 41晶体中大的磁振子热导率。此外，从测量的总比热和声子态密度确定的磁振子比热，并表现出肖特基异常，由于带隙的自旋链的磁振子模式。这些发现提供了新的见解声子和磁振子动力学和无公度磁性晶体，包含低维子结构的热输运性质。
Inverse-design of two-dimensional magnonic crystals via topology optimization with frequency-domain micromagnetics
Tokyo University of Science（东京科学大学）；Yokohama National University（横滨国立大学）；University of Tsukuba（筑波大学）；National Institute for Materials Science (NIMS)（国立材料研究所）
Topologically protected magnon surface states are highly desirable as an ideal platform to engineer low-dissipation spintronics devices. However, theoretical prediction of topological magnons in strongly correlated materials proves to be challenging because the ab initio density functional theory calculations fail to reliably predict magnetic interactions in correlated materials. Here, we present a symmetry-based approach, which predicts topological magnons in magnetically ordered crystals, upon applying external perturbations such as magnetic/electric fields and/or mechanical strains. We appl…
