Thickness dependent terahertz emission from cobalt thin films.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Ultrafast Optics

Background:

• Terahertz (THz) pulse emission from magnetic materials is a key phenomenon in spintronics and ultrafast magnetism.
• Understanding the relationship between film properties and THz emission characteristics is crucial for developing novel THz sources and devices.
• Cobalt thin films are promising candidates for such applications due to their magnetic properties.

Purpose of the Study:

• To investigate the influence of cobalt thin film thickness on terahertz (THz) pulse emission characteristics.
• To determine the role of in-plane versus out-of-plane magnetization components in THz emission.
• To correlate magnetic properties with observed THz emission phenomena.

Main Methods:

• Illumination of cobalt thin films with femtosecond laser pulses.
• Detection and analysis of emitted terahertz (THz) pulses.
• Rotation of the sample about the surface normal to study azimuthal angle dependence.
• Magnetic force microscopy (MFM) to characterize film magnetization.

Main Results:

• For cobalt films < 40 nm, THz electric field direction rotates with sample rotation (azimuthal angle-dependent), indicating in-plane magnetization influence.
• For thicker films (> 40 nm), an azimuthal angle-independent THz emission component emerges, attributed to out-of-plane magnetization.
• The contribution of the out-of-plane magnetization component to THz emission increases with film thickness.

Conclusions:

• Cobalt thin film thickness is a critical parameter controlling the nature of laser-induced THz emission.
• The transition from in-plane to out-of-plane magnetization dominance with increasing thickness directly impacts THz emission anisotropy.
• These findings provide insights into the mechanisms of THz generation in magnetic thin films and guide material design for tailored THz emission.