Search for magnon-phonon coupling effect in metallic triangular antiferromagnet CrB2

Spin dynamics of non-collinear magnetic structures can exhibit the rare phenomena which go beyond the linear spin wave theory. Our previous studies on non-collinear antiferromagnetic insulators (Y, Lu)MnO3 at ISIS showed that magnon-magnon/phonon interactions indeed have a sizable effect on the spin dynamics. To extend this concept to metallic systems, we have recently carried out an inelastic neutron scattering experiment at MAPS on CrB2, a metallic triangular antiferromagnet with non-collinear magnetic structure. Along with successful measurements of magnons over a large momentum-energy space, we observed that some phonon modes near the magnon modes have unusual behavior, which is also seen in (Y, Lu)MnO3. To confirm that this anomaly comes from magnon-phonon coupling, we propose to investigate the phonon spectra of CrB2 at 150 K, the temperature above TN =88 K where magnons disappear.

非共线磁结构的自旋动力学可展现出超越线性自旋波理论的罕见现象。我们此前在ISIS装置上针对非共线反铁磁绝缘体(Y, Lu)MnO3开展的研究表明，磁振子-磁振子/声子相互作用确实对自旋动力学存在显著影响。为将这一研究思路拓展至金属体系，我们近期在MAPS谱仪上针对CrB2开展了非弹性中子散射实验：CrB2是一种具有非共线磁结构的金属性三角反铁磁体。在成功完成大动量-能量范围内的磁振子测量后，我们观测到磁振子模式附近的部分声子模式存在反常行为，这一现象在(Y, Lu)MnO3中也有出现。为确认该反常现象源自磁振子-声子耦合，我们提议在150 K（高于磁振子消失的奈耳温度TN=88 K）下对CrB2的声子谱开展研究。