Carbon Nanotube Based Magnetic Tunnel Junctions (MTJs) for Spintronics Application

Abstract

Spintronics devices exploiting the spin of the electron [1-10] are prepared to revolutionise the electronics industry. The significance of this new generation device is faster memory and lower power consumption at low electron density. The late 20th century has been considered as an era of microelectronics. However, the avalanche growth of microelectronics is a major threat to Moore’s law and spintronics may be a solution for it. From the first transistor to the signally powerful microprocessor in our recent computers, most electronic devices have employed circuits that express data as binary digits, or bits (1 and 0) represented by the existence or absence of electric charge. Unlike microelectronics, spintronics exploits spin (spin up ↑ and spin down ↓) of the electron to carry information between devices. The discovery of Giant Magnetoresistance (GMR) by Nobel Prize winners Albert Fert and Peter Grunberg had actually led to the birth of novel field spintronics [11]. Currently, most of the existing spintronic devices [12] are based on metallic systems such as magnetic tunnel junctions (MTJs) and single electron transistor [13]. On the other hand, a wealth of intriguing spin phenomena has been observed in nanoscale materials [14]. This triggered an extensive research effort on spin transport in nanoscale MTJs and other interesting phenomena were realised. One of the most important phenomena is tunnel magnetoresistance (TMR) of the MTJs. A MTJ is composed of two ferromagnetic conducting layers separated by an ultra-thin insulating layer [15-20]. The TMR was first demonstrated by M. Julliere [21]. Yakushiji et al. [22] experimentally demonstrated the influence of spin conduction on TMR. The enhancement and oscillation of TMR in ferromagnetic multiple junctions have been predicted by several authors [23-30]. However, there have been only a few experiments on spin-dependent single electron tunnelling (SET) to date [31-36] due to the difficulty in fabricating appropriate sample structures for spin-dependent SET. The desire to build spintronic devices that show larger spin dependent phenomena has led many researchers to combine single electron tunneling (SET) and spin dependent electron tunneling (SDT). The charge quantization in low capacitance magnetic tunnel junctions