Spin Electronics: Magnetic Moments and Amorphous Semiconductors

Abstract

Spin electronics in its broadest definition is the study of systems where both the charge and the spin of the electron play a role. The term was originally intended as a new technological concept, where traditionally the electron’s charge is important because transistors rely on currents and voltages, while the electron’s spin is important only in magnetic materials used for memory; spin electronics represents a new hybrid system. Examples range from technological developments such as MRAM (magnetic random access memory) that are based on magnetic tunnel junctions, to some forms of quantum computing. More broadly, spin electronics can be viewed as the visibility of and strong interactions between charge and spin in highly correlated electron materials such as high Tc superconductors, colossal magnetoresistance manganites, and doped semiconductors near the metal-insulator transition. I will discuss why these materials show such unusual spin-charge properties, and efforts to introduce magnetic moments into semiconducting materials, focusing particularly on our work on amorphous Si doped with magnetic ions such as Gd or Mn. These alloys possess dramatic magnetic and transport properties due to electron-electron and electron-local moment interactions, including enormous (many orders of magnitude) negative magnetoresistance. These amorphous materials provide an important counterpart to the more traditionally studied crystalline magnetically-doped semiconductors.