Spin Transport in Nanowires Synthesized Using Anodic Nanoporous Alumina Films

Spin transport in restricted dimensionality structures (e.g., nanowires) have unusual features not observed in bulk samples. One popular method to synthesize nanowires of different materials is to electrodeposit them selectively within nanometer diameter pores in anodic alumina films. Different materials can be sequentially deposited within the pores to form nanowire “spin valves” consisting of a spacer nanowire sandwiched between two ferromagnetic nanowires. This construct allows one to study spin transport in the spacer nanowire, with the ferromagnetic contacts acting as spin injector and detector. Some of our past work related to the study of spin transport in organic and inorganic nanowire spin valves produced using nanoporous anodic alumina films is reviewed in this chapter

Information Processing with Electron Spins

Information processors process information in a variety of ways. The human brain processes information through a highly interconnected system of neurons and synapses, while a digital computer processes information by having a binary switch toggle on and off in response to a stream of binary bits. The “switch” is the most primitive unit of the modern computer. The better it is (faster, more energy efficient, more reliable, etc.), the more advanced is the computer hardware. Energy efficiency, however, is more important than any other attribute, not so much because energy is costly, but because too much energy dissipation prevents increasing the density of switches on a chip that is necessary to make the chip increasingly more powerful. Reducing dissipation entails radically new and often revolutionary approaches for implementing the switch. One such approach is to encode digital bit information in the spin polarization of a single electron (or ensemble of electrons) and then using two mutually antiparallel polarizations to represent the binary bits 0 and 1. Switching between the bits can be accomplished by simply flipping the polarizations of the spins, which takes very little energy. Such switches are extremely energy efficient if designed properly, but they are somewhat slower than traditional transistor-based switches and can be more error prone. This paper discusses the pros and cons of spin-based switches and introduces the reader to the most recent advancements in information processing predicated on encoding information in electron spin polarization

Nanomagnetic Boolean Logic -- The Tempered (and Realistic) Vision

The idea of nanomagnetic Boolean logic was advanced more than two decades ago. It envisaged the use of nanomagnets with two stable magnetization orientations as the primitive binary switch for implementing logic gates and ultimately combinational/sequential circuits. Enthusiastic proclamations of how nanomagnetic logic will eclipse traditional (transistor-based) logic circuits proliferated the applied physics literature. Two decades later there is not a single viable nanomagnetic logic chip in sight, let alone one that is a commercial success. In this perspective article, I offer my reasons on why this has come to pass. I present a realistic and tempered vision of nanomagnetic logic, pointing out many misconceptions about this paradigm, flaws in some proposals that appeared in the literature, shortcomings, and likely pitfalls that might stymie progress in this field.Comment: Accepted in IEEE Acces

Energy dissipation and switching delay in stress-induced switching of multiferroic devices in the presence of thermal fluctuations

Switching the magnetization of a shape-anisotropic 2-phase multiferroic nanomagnet with voltage-generated stress is known to dissipate very little energy ($<$ 1 aJ for a switching time of $\sim$0.5 ns) at 0 K temperature. Here, we show by solving the stochastic Landau-Lifshitz-Gilbert equation that switching can be carried out with $\sim$100% probability in less than 1 ns while dissipating less than 2 aJ at {\it room temperature}. This makes nanomagnetic logic and memory systems, predicated on stress-induced magnetic reversal, one of the most energy-efficient computing hardware extant. We also study the dependence of energy dissipation, switching delay, and the critical stress needed to switch, on the rate at which stress is ramped up or down