RFeO₃ Ultrafast Optomagnetic Interaction With THz Pulse

In the past decade, there is a rapidly growing interest in physics, chemistry, advanced materials and catalysis of perovskite-type RFe O3. The ultrafast opto-magnetic interaction between RFe O3 and THz pulse may trigger more attention for deeper insight on ultrafast phenomenon, and the development of new spintronics devices. We focused on the dynamic motion of spin and free induction decay(FID) with ultrafast THz pulse. Through the magnetization research and THz time domain(THz-TDS) spectroscopy, we studied the selected excitation of ferromagnetic(FM) and antiferromagnetic(AFM) modes of Pr Fe O3. And pay attention to the temperature and magnetic field induced spin reorientation transition of Nd Fe O3. The main research work is summarized as follows:(1) Through the transmission-type THz time domain spectrum, the coupling between THz magnetic pulse and coherent spin of Pr Fe O3 has been researched. The ferromagnetic and antiferromagnetic mode are excited with different rotational angle between the direction of THz pulse and c axis of Pr Fe O3. The dependence of FID frequency, intensity and polarization direction on rotational angle has been studied. Moreover, the optical parameters of THz range is analyzed through the data of THz-TDS.(2) The spin reorientation transition in single crystal Nd Fe O3 is studied using AC magnetic susceptibility, hysteresis loops, and polarized THz time domain spectroscopy measurements. Different frequency dependent behaviors of AC susceptibility reflect that the dynamic response of magnetization inside the spin reorientation region differs from that outside the transition region. The magnetization hysteresis loops at different temperatures reveal that the special spin reversal in the reorientation process, which coincides with the abrupt increase of AC magnetic susceptibility at the transition points. In addition, temperature dependent THz wave excitation of AFM mode indicates the process of spin reorientation as a continuous rotation of Fe3+ spins rather than a mixed phase of Γ4 and Γ2.(3) Temperature-induced spin reorientation transition in Nd Fe O3 is studied by THz-TDS. Following the resonant excitation of AFM mode, the nature of temperature dependence of emission is investigated systematically in the spin reorientation temperature interval. The emission frequency is observed at 0.485 THz for Г4 phase, and it gradually reduces to 0.456 THz(around 110 K) corresponding to Г2 phase. The evolution of vector G is obtained from the temperature-dependent polarization changes of the AFM mode excitation.(4) By using THz-TDS and hysteresis loops, we show that the magnetic-field induced SRT of Nd Fe O3 between Γ4 and Γ2 is strongly anisotropic, depending on the direction of the applied magnetic field. Our experimental results are well interpreted by the anisotropy of rare-earth Nd3+ ion. Furthermore, we find that the critical magnetic-field required for spin reorientation transition can be modified by changing the temperature. Our study suggests that the anisotropic spin reorientation transition in Nd Fe O3 single crystal provides a platform to facilitate the potential applications in robust spin memory devices.