Ferromagnetic Resonance Study of Magnetic Tunnel Junction Pillar Arrays: Effects of Insulator Thickness
摘要
Magnetic tunnel junction (MTJ) molecular spintronics device (MTJMSD) research is an emerging field in molecular spintronics. Typically, they consist of two ferromagnetic electrodes (FMs), separated by an oxide spacer, that are bridged by thiol-terminated paramagnetic molecules. MTJMSDs are a new type of MTJ and serve as a research platform for mechanistic investigations and the design of novel devices and metamaterials. These devices have demonstrated robust exchange coupling and large shifts in tunneling magnetoresistance (TMR) at room temperature. Little is known about how insulator thickness, typically 2 nm, affects those properties. In this study a series of MTJ samples, with aluminum oxide thickness from 0 nm to 2.1 nm, were evaluated via x-band ferromagnetic resonance (FMR). FMR results show that as little as 1 angstrom of aluminum oxide can decouple the FMs’ resonances, indicating suppression of metallic-like exchange and shorts. However, ultrathin insulators (0.1–0.4 nm) exhibit signs of weak interlayer coupling, in that their resonance peaks shift from the isolated reference films’ peak positions. Samples in the 0.5–2.1 nm insulator range are largely unchanged from the reference films consistent with more robust decoupling. These results demonstrate that MTJMSDs can be fabricated with insulators far thinner than 2 nm while maintaining decoupled FMs and suppressing metallic-like exchange. Thinner insulators enable the fabrication of MTJMSDs with an increased number of molecules correctly oriented for FM bridging and the use of a wider variety of molecules. Both factors improve device tunability and facilitate the development of novel MTJMSD-based devices and applications.
Graphical Abstract