The Nobel Prize in Physics 2007: Giant Magnetoresistance. An idiosyncratic survey of spintronics from 1963 to the present: Peter Weinberger's contributions

Abstract

While the twentieth century was dominated by advances in controlling electrical currents through the charge of the electron, aka electronics, the rapid developments since 1988 have lead to a control of currents through the spin of the electron, i.e., spintronics. The groundwork for this field comes from studies on metallic alloys and multilayers started in the early 1960s. Due to parallel developments in the growth of semiconductor heterostructures, e.g., molecular beam epitaxy, work on metallic layers rapidly advanced in the late 1970s and early 1980s. By 1988 groups lead by Fert and Grünberg were able to grow metallic multilayers which displayed the sought after effect; a small magnetic field was able to dramatically change the electric resistance of the structures. This led to an immediate explosion in activity in this area; so much so that the materials which display this effect were incorporated in the read-heads of hard disk drives of computers by 1997.

I will focus on developments in three distinct time periods. The first was from 1988 to 1995 which was dominated by metallic multilayers which displayed giant magnetoresistance (GMR), the second from 1995 to 2000 when reproducible magnetic tunnel junctions (MTJs) were studied for their tunnelling magnetoresistance (TMR), and the third period from 2000 to 2005 in which the ideas of Berger and Slonczewski were realized on the back action of currents on the magnetic background of the materials doing the conducting, i.e., current induced magnetization switching (CIMS). The contributions of Peter Weinberger to these developments illustrate the broad range of his activities in spintronics, this field which is barely twenty years old.

Keywords:

• spintronics
• GMR
• TMR
• electronic transport
• ferromagnetism

Notes

Notes

1. Read-heads based on this idea (US patent no. 5 159 513) went into production in 1997.

2. for example take two magnetic layers 90° to one another separated by a non-magnetic metallic spacer; if you set up the boundary conditions such that a spin current enters with its plane of polarization parallel to the background magnetization (in equilibrium) in one layer it will exit the other layer (into the second lead) with its plane of polarization parallel to the equilibrium magnetization of the second layer at 90° to the first. The evolution Jianwei Zhang and I found 58–60 is that the plane of polarization continuously rotates from being parallel, to being 45° away from the equilibrium magnetization of the first layer; and in the second layer the plane of polarization starts out 45° away from its equilibrium magnetization (which is 90° relative to the first layer) and rotates continuously until it is parallel to the magnetization before exiting the active region into the spin-polarized lead region. All of this large angle rotation of the spin current occurs for tiny reorientations of the background magnetization when the system is out-of-equilibrium, i.e., tiny transverse spin accumulations that rotate the magnetization by a minute angle lead to spin currents that have a plane of polarization that deviates considerably from the background magnetization.