Spintronics: from Lord Kelvin to...

Master in NanoscienceLow Dimensional SystemsLectures by A. Rubio and N. Zabala

Spintronics: from Lord Kelvin to Nanotechnology

E. J. G. Santos

Lord Kelvin and your hard drive

Master in NanoscienceDonostia – San Sebastian, January 31th 2008

Lord Kelvin predicted the ‘’new’’ solid state property in 1857.

“ … I have already communicated to the Royal Society a describtion of experiments by which I found that iron, when subjected to magnetic force, acquires an increase of resistance to the conduction of electricity across, the lines of magnetization. By experiments more recently made, I have ascertained that the electric conductivity of nickel is similarly influenced by magnetism, but to a greater degree, and with a curious diference…”

Proceedings of the Royal Society of London, Vol. 8, 1857, pp. 546550

What’s so interesting about this 148 years old experiment?“ … He oppened the door for a number of effects that couple magnetization to electrical resistance …”Nichol´s Encyclopedia of Physical Sciences.

The underlying concepts:Ferromagnetism and Electronic Transport

Anisotropic magnetoresistance (AMR)

Ordinary magnetoresistance (OMR)

Giant magnetoresistance (GMR)

Tunneling magnetoresistance (TMR)

Ballistic magnetoresistance (BMR)

Colossal magnetoresistance (CMR)


The same principles for each or not?

‘ ’ … ” almost” the same (… ). Surely you’ re joking, Mr. Feynman …(… )”Adventures of a Curious Character (W. W. Norton & Company, Inc. 1997)

Resistance and magnetization: dependence on scattering features


The electrical resistance in a conductor arises when electrons scatter against irregularities in the material so that their forward movement is obstructed.

In a magnetic conductor the direction of spins of most electrons is parallel with the magnetization (red). A minority of electrons have spin in the opposite direction (white).

Information for the Public, The Royal Swedish Academy of Sciences 2007


Giant Magnetoresistance GMRIf the direction of the magnetization is the same in both magneticlayers the electrons with parallel spin (red) can pass through the system without problems.

If the direction of magnetization in the two magnetic layers is opposed, all the electrons will have antiparallel spin in one of the layers and will therefore scatter a great deal.

Information for the Public, The Royal Swedish Academy of Sciences 2007


GMR Mechanism

5.118.1

)2sin(12

==

+

∝

F

Rup

F

Ru

pt

t

J

λ

λπφ

The exchange coupling is shown to oscillate

about zero changing sign back and forth from FM and AFM. PRB 44, R7131 (1999)

12J

The value of p is in good agreement with theoretical predictions of 2 for the planar geometry.

Baibich et. al, PRL 61, 2472 (1988)Binasch et. al, PRB 39, R4828 (1989)


The birth of Spintronics


“…for the discovery of Giant Magnetoresistance…”The Nobel Prize in Physics 2007Nobelprize.org

Albert Fert,France

Peter Grünberg,Germany


Electronics + …

Electron as seen by an electronician

Applications: logic gates RAM

Inconvenients: volatility of the information energy consumption limited density of information

Figures from P. Bruno’ talk, MPI, Halle, Germany.

MOSFET


… Magnets

Electron as seen by a magnetician

The charge of the electrons plays a secondary role.Applications: mass storage of information

(magnetic disks and tapes)

Advantages: nonvolatility high storage density no energy consumption

Inconvenients: mechanical acess to information


Charge + Spin = Spintronics



Purpose of Spintronics: ‘’… perhaps, teaching electrons new tricks …”Herbert Kroemer (2001)

•New fundamental physical questions

•New phenomena

•New devices and applications

TTTTCC

MM


New devices but with an old problem

Courtesy A. Ernst


Basic ingredients for the new devices1. Ferromagnetic Metal

2. Semiconductor based spin electronic devices

Devices for the manipulation of single spin (quantum computing)

The idea: Electron spins could be used as qubits. They can be up or down, but also in coherente superpositions of up and down states.


• Supriyo Datta and Biswajit Das in 1989 proposed the first spintronic device.

• It works with an electrode made of a ferromagnetic material (purple) that emits spinaligned electrons, which pass through a narrow channel controled by the gate electrode and are collected by the another ferromagnetic electrode.

Igor Zutic et. al, RMP 76, 323 (2004)

The First Spintronic Device


ConclusionsThe GMR is the background to switch from the ‘’traditional’’ electronic to the

spin one based.

Spintronics has a great potentiality for applications and it is in the beginning of its journey.

The Semiconductor Spintronics are the new generation for devices, not only for the many advantages (e.g. quantum mechanically stable, new functionality,

lower energy consumption/less heating, …) but for the exciting new physics that there is.

The “disadvantages” of Semiconductor Spintronics (e.g. electron spin not conserved) open new gates for the young and senior, as well, scientists work in

pratical and underlying questions. New opportunities are caming up!

So, …

…who is who in Spintronics.



Thanks for your attention!

Just for helping …

Pseudocubic perovskite manganite (La0.7Sr0.3MnO3 are electrically connected by a single multiwall CNT.

At low temperatures, the conduction in LSMO exhibts a very high spinpolarization 100%.

Spintronics: from Lord Kelvin to...

Documents

Transcript of Spintronics: from Lord Kelvin to...