Magnetismo Ivan S. Ferreira, 05/09/2016

Origem •

E(t) e J;

•

Momentum angular;

•

Spin (e, núcleo, neutrino).

Stern-Gerlach experiment In experiment, a beam of silver atoms were passed through inhomogeneous magnetic field and collected on photographic plate. Since silver involves spherically symmetric charge distribution plus one 5s electron, total angular momentum of ground state has L = 0. If outer electron in 5p state, L = 1 and the beam should split in 3.

Stern-Gerlach experiment However, experiment showed a bifurcation of beam!

Gerlach’s postcard, dated 8th February 1922, to Niels Bohr

Since orbital angular momentum can take only integer values, this observation suggests electron possesses an additional intrinsic “⇣ = 1/2” component known as spin.

Propriedades fundamentais

Domínios Magnéticos

Relevance of nanomagnetism

6 A.P. Guimarães CBPF

Areas of influence of nanomagnetism

7 A.P. Guimarães CBPF

Bader 2005

Evolution of magnetic recording

Three generations of magnetic hard disks

Areal density evolution A.P. Guimarães CBPF

9

IBM

The importance of magnetic recording Magnetic 92%

About 10 exabytes=1019 bytes Film 7.5%

Paper and optical 0.03%

10

Proportion of data stored under different forms in 2003 (UCBerkeley 2004)

A.P. Guimarães CBPF

Spin dependent resistance and giant magnetoresistance (GMR) The electrical resistance depends on the relative orientation of electron spin and magnetization of the layer

Applying a field to change from antiparallel to parallel magnetization changes the resistance 36 A.P. Guimarães CBPF

Applications of GMR

Magnetic random access memory (MRAM) using a tunnel junction (Wolf 2001) A.P. Guimarães CBPF

Reading head using GMR (Prinz 1998)

37