High time-resolution measurement of transient magnetism using opto-electric response

实验证明，磁性材料对光照射的磁响应是多种多样的。当材料受到顺磁复合体的圆偏振光照射时，角动量被传递到自旋系统，从而导致自旋取向上的不同极性，这取决于自旋-轨道耦合对称性所产生的吸收带。对于S=5/2的有机溶液中的Fe(III)自旋体系，在垂直于光束的外磁场中，成功地探测到了光致塞曼相干作为自由感应衰变信号。另一方面，与光的偏振无关，在磁场存在的情况下，光引发的塞曼态混合产生绝热的自旋取向，并且表现出特征的磁场依赖性。在特定情况下，这种态混合的自旋取向有助于区分单核复合体和双核复合体。对于磁有序体系，尽管光辐射的磁响应大多源于热注入，但有趣的光触发效应，如快速的场壁振荡和磁化反转，取决于外加磁场、光强和温度。上述各种光响应都可以在纳秒的时间分辨率下检测到。这些反应强烈地表明了进一步提高磁探测的时间分辨率的兴趣和重要性。

It is elucidated experimentally that the magnetic response to light irradiation is very diverse in magnetic materials. When the material is irradiated by a circularly polarized light for paramagnetic complexes angular momentum is transferred to the spin system giving rise to different polarities in spin orientation depending on the absorption bands resulting from the symmetry of spin-orbit coupling. Also, for Fe(III) spin system in organic solution with S=5/2 photo-induced Zeeman coherence was successfully detected as a free-induction decay signal in the external magnetic field perpendicular to the light beam. On the other hand regardless of light polarization optically initiated Zeeman state mixing in the presence of magnetic field creates adiabatic spin orientation and exhibits characteristic magnetic-field dependence. For a particular case such a spin orientation by the state mixing can contribute to identification of mono-nuclear complex and di-nuclear complex. For magnetically ordered systems although the magnetic responses to light irradiation are mostly those originating from heat injection, interesting photo-triggered effects such as the fast domain-wall oscillation and magnetization inversion depending on the applied magnetic field, light intensity, and temperature.A variety of photo-responses mentioned above are all detected with the nanosecond time resolution. These responses strongly suggest interest and importance of further improvement of time resolution in magnetic detection.