Ultrasensitive Terahertz Spintronic Modulator for On‐Chip Applications

Ensuring stability and controlling terahertz spintronic emitters typically involves the application of a relatively strong magnetic field to counter magnetization drift during repeated pumping to regulate the emitted terahertz radiation's direction. However, using a strong magnetic field is practically not relevant for on‐chip compact, low‐cost ultrawide broadband terahertz opto‐spintronic devices. Uniaxial magnetic anisotropic materials provide a potential avenue to stabilize as well as control the ultrafast spin current pulses, at weak magnetic field specifically weaker than the anisotropy field. Here, we report the amplitude modulation as well as polarization switching of the terahertz spin current pulse at magnetic field less than 1 Oe, demonstrating an ultrasensitive spintronic emitter. In comparison to the use of a strong magnetic field, our repeated measurements demonstrate that there is no magnetization drift, rendering the need for a strong magnetic field unnecessary. Our findings establish a uniaxial magnetic anisotropic emitter with ultra‐strong modulation as a promising candidate for future efficient ultrafast on‐chip opto‐spintronic devices.