Recent developments in the controlled movement of domain walls in magnetic nanowires by short pulses of spin-polarized current give promise of a nonvolatile memory device with the high performance and reliability of conventional solid-state memory but at the low cost of conventional magnetic disk drive storage. The racetrack memory described in this review comprises an array of magnetic nanowires arranged horizontally or vertically on a silicon chip. Individual spintronic reading and writing nanodevices are used to modify or read a train of ∼10 to 100 domain walls, which store a series of data bits in each nanowire. This racetrack memory is an example of the move toward innately three-dimensional microelectronic devices.

http://science.sciencemag.org/content/sci/320/5873/190.full.pdf

Magnetic Domain-Wall Racetrack Memory

We consider an Ising model in which the spins are coupled by infinite-ranged random interactions independently distributed with a Gaussian probability density. Both "spinglass" and ferromagnetic phases occur. The competition between the phases and the type of order present in each are studied.

Solvable Model of a Spin-Glass

(2001). The mean free path of electrons in metals. Advances in Physics: Vol. 50, No. 6, pp. 499-537.

/pdf/the-mean-free-path-of-electrons-in-metals-4jbak142d3.pdf

The mean free path of electrons in metals

In a discussion of conduction in glasses containing transition metal ions, the following points are stressed: 1. (a) The process is similar to “impurity conduction” in doped and compensated semi-conductors. 2. (b) There should be two terms in the activation energy, the Miller-Abrahams term and a polaron hopping term. 3. (c) Both terms should tend to zero, giving a decreasing slope of the ln p versus 1/T curve, as T → 0. 4. (d) The Heikes-Ure formula for the thermopower is discussed and a tentative explanation given of the difference between vanadium- and iron-containing glasses.

Conduction in glasses containing transition metal ions

A discussion is given of some aspects of the metal insulator transition. Particular attention is paid to the status of the “minimum metallic conductivity”. The concept is valid for liquids, and in some, but not all, solid systems.

H. Jones

Papers

The Theory of the Properties of Metals and Alloys