Title: Ferromagnetic materials for energy efficient computing

Abstract

In ferromagnetic (FM) materials, the electrical resistivity and mobility experienced by the spin-up and spin-down electrons are different. The asymmetry in the electron mobility for different spins is indirectly caused by the asymmetry in the electron density-of-state (DOS). When current passes from a FM metal to a nonmagnetic (NM) metal via an ohmic contact, spin-polarized current is obtained in the NM due to the mobility asymmetry (indirectly due to DOS asymmetry) in FM. Similarly, when current passes from FM to NM via an insulator (tunneling contact), spin-polarized current is obtained in the NM directly due to the DOS asymmetry in FM. Therefore, FM can be used as spin-polarizer in spintronics circuits. Although a significant amount of spin polarization arises in FM metals, this is inadequate for spin-based applications. Hence, non-equilibrium spin must be introduced in semiconductor (SC) to make advanced spin-based devices. SC based spintronics can combine the well-known advantages of SC materials. Magnetic tunnel junction (MTJ) is a spintronic device that enables us to use the spin property of electrons along with the charge. It is composed of two ferromagnetic layers and a dielectric layer sandwiched in between them. One of the two ferromagnetic layers is strongly magnetized and is known as a pinned layer or reference layer, as its direction of magnetization cannot be changed. The other ferromagnetic layer is weakly magnetized and is known as the free layer; its direction of magnetization can be changed. MTJ has two states: the low-resistance state is termed parallel (P), whereas the high-resistance state is termed anti-parallel (AP). Many switching mechanisms have been proposed to switch the state of MTJ from P to AP or vice versa, namely, spin-transfer torque (STT), spin Hall-assisted STT (SHE-STT), and voltage-controlled magnetic anisotropy (VCMA). Among them, STT switching mechanism is the most practicable and well-founded method for constructing MTJs. MTJ have gained special attention because of its non-volatility, high speed, almost zero leakage power consumption, and, most importantly, compatibility with semiconductor devices. This device is a promising candidate for building high-performance, high-density, and low-power arithmetic functions. Magnetic full adder (MFA), multiplier, logic functions, shifters based on nonvolatile memory has been designed that defeat the communication obstruction between memory units and distinguish logic blocks. The logic in memory (LIM) architecture overcomes the bottleneck of von-neumann architecture in terms of delay and power linked with data movement. The logic in memory (LIM) architectures demonstrated better performance that can be used as energy efficient computing systems.