Abstract
We report a universal terahertz (THz) emission behavior from simple Ni, Fe, and Co metallic ferromagnetic films, triggered by the femtosecond laser pulse and subsequent photoinduced demagnetization on an ultrafast time scale. THz emission behavior in ferromagnetic films is found to be consistent with initial magnetization states controlled by external fields, where the hysteresis of the maximal THz emission signal is observed to be well-matched with the magnetic hysteresis curve. It is experimentally demonstrated that the ultrafast THz emission by the photoinduced demagnetization is controllable in a simple way by external fields as well as pump fluences.
The creep evolution was followed by conducting magnetic measurements on ferromagnetic steel samples exposed to different creep strains at a constant temperature. 410 stainless steel (410 SS) rods were submitted to creep at 625°C applying a constant stress of 124 MPa for different creep times. A magnetic hysteresis curve was generated for every sample. It was found that the shape of the hysteresis curves varied with creep time. The extent of creep was assessed by measuring magnetic saturation, coercivity, and remanence. The changes in microstructure due to creep are related to variations in magnetic properties, which are explained in terms of possible magnetic domain pinning. It was observed that the microstructural changes due to creep are better correlated with the coercivity of the material. In summary, it is feasible to use a magnetoelastic sensor to detect the partial level of creep in a ferromagnetic material by nondestructive examination.
Universal field-tunable terahertz emission by ultrafast photoinduced demagnetization in Fe, Ni, and Co ferromagnetic films
