Comparisons of magnetic defects and coercive forces for Co/Si(100) and Co/rubrene/Si(100).

Spintronics can add new functionalities to electronic devices by utilizing the spin degree of freedom of electrons. Investigating magnetic defects is crucial for the performance of spintronics devices. However, the effects of magnetic defects that are introduced by the presence of organic materials on their magnetic properties remain unclear. Herein, we report on a novel method using rubrene combined with Kerr microscopy that enables quantitative and direct measurements of magnetic defect density. For Co/Si(100) at a magnetic field near the coercivity value, Kerr microscopy images show a dark image with some magnetic defects. Because of domain wall motion, small patches gradually change the contrast. These magnetic defects are immovable at different magnetic fields and serve as pinning sites for domain wall motion. Experimental evidence shows that coercive force can be reduced by controlling the magnetic defect density by introducing small amounts of rubrene into the films. Furthermore, direct quantitative measurements of magnetic defects show both a one-dimensional bowing of domain walls and strong defect-domain wall interactions in the films. Based on these findings, we propose a viable strategy for reducing the coercive force of Co/Si(100) by controlling the magnetic defect density and this new information promises to be valuable for future applications of spintronics devices.

Variations of the elastic modulus perpendicular to the surface of rubrene bilayer films.

Investigations exploring the inherent mechanical properties of electronic materials have grown rapidly in recent years largely because they are important in developing flexible electronics, organic displays and sensors. However, our understanding of the mechanical properties of organic semiconductors with a thin-film form remains limited. We report herein on an investigation of the structures and related elastic moduli perpendicular to the surface of a rubrene thin film. A rubrene/Si(100) film typically has a cluster-type morphology mainly comprising crystalline nanodomains within the film. We propose a structural bilayer model that can be used to explain the layered nature or characteristics of the rubrene films. As the film thickness is increased, the enhancement in elastic modulus can be attributed to the presence of a soft surface layer on a hard underlayer. Based on four-point probe measurements, the bilayered nature of such materials can be used to characterize their electrical resistive behavior while interfacial roughness is sensitive to the transport paths of conduction electrons. This information is valuable for future applications of organic semiconductors in flexible devices.