Magnetization Dynamics of CoFe Thin Films Grown by Pulsed Laser Deposition

Abstract

Magnetic damping plays a pivotal role in devices harnessing the electronic spin degree of freedom, significantly influencing their energy efficiency and operational speed. Despite its crucial role, the persistently high Gilbert damping in common ferromagnetic materials, typically on the order of 10−3, presents a challenge for applications in spintronics and spin-orbitronics that require materials with ultra-low damping characteristics. Alternative materials, such as Heusler alloys and magnetic insulators, have showcased significantly lower damping coefficients below 10−4, primarily due to the absence of conduction electrons. Unfortunately, despite their low damping attributes, these materials pose growth challenges and are incompatible with the widely used Complementary Metal-Oxide-Semiconductor (CMOS) technology, limiting their practical utility. Recent developments in material science search for low-damping material, introduce promising prospects. Cobalt and iron binary alloys, particularly Co20Fe80, challenge the conventional limitations by exhibiting relatively low damping coefficients. Theoretical predictions by Mankovsky et al. propose a damping coefficient of 5 × 10−4 in Co20Fe80, highlighting a unique band structure with a sharp minimum in the density of states at the Fermi level. This minimum aligns with the alloy concentration where the least magnetic damping occurs. Subsequent experimental studies by Schoen et al. validate these theoretical predictions, underscoring the potential of Co20Fe80 alloys as materials with minimal damping characteristics. The focus of this thesis is to study the magnetization dynamics of Co60Fe40 thin films prepared through Pulsed Laser Deposition (PLD). The overarching goal is to develop high-quality nanometer-thick films. The investigation kicks off by scrutinizing the characteristics of CoFe films under diverse deposition parameters, manipulating laser energy and temperature to discern optimal conditions. Once these optimal parameters are identified, a systematic exploration of thickness dependence follows, encompassing variations in the CoFe layer thickness within the range of 10 to 25 nm. Moreover, the study extends to exploring the spin-pumping effect in bilayers of CoFe/Pt. In this aspect, the thickness of the Pt layer is systematically varied, enabling the calculation of the spin diffusion length in Pt. This meticulous and systematic study aims to yield valuable insights applicable to the realms of magnonics, spintronics, and spin Hall devices.