Effect of thickness on tuning the perpendicular coercivity of Ta/CoFeB/Ta trilayer

Abstract

In the present investigation, a systematic study has been undertaken to explore the effect of magnetic layer film thickness on the structural, topographical, magnetic and electrical transport properties of the Ta(5 nm)/CoFeB(2–100 nm)/Ta(3 nm) trilayer. We show that the perpendicular coercivity (Hc_┴) and the saturation magnetization (M_s) of Ta/CoFeB/Ta are very sensitive to the CoFeB film thickness. A large Hc_┴ with small M_s is realized for 50 nm thick CoFeB film at a growth temperature (T_s) of 475 °C. Hc_┴ started to develop at a considerable film thickness of 25 nm and reached a maximum at 50 nm and then decreased when the film thickness increased up to 100 nm. Magnetic studies of Ta/CoFeB (bottom) and CoFeB/Ta (top) interfaces confirm that the major contribution to the perpendicular coercivity of the stacks come from the bottom interface. The topography of the films is found to be affected by the film thicknesses. AFM displays larger grain sizes for thicker CoFeB films, however the nano crystallites embedded in the larger grains could not be detected by XRD analysis. The high resistivity values obtained from Hall resistivity measurements further confirms the non-crystalline nature of the CoFeB film. The presence of boron and other elements (Ta, Co, and Fe) are evident from the X-ray Photoelectron spectroscopic (XPS) studies. The Ta/CoFeB/Ta trilayer system being amorphous possessing high Hc_┴, with small M_s can be enabled for the development of high-density data storage, spin logic gates and nonvolatile memories in low power consuming spintronics devices.