Grünberg Found Useful Effect That Went Against Then-Dominant Theory

(p. A25) Peter Grünberg, a Nobel-Prize-winning physicist who discovered how to store vast amounts of data by manipulating the magnetic and electrical fields of thin layers of atoms, making possible devices like the iPad and the smartphone, has died at 78.
. . .
Since the British physicist Lord Kelvin first wrote about the subject in 1857, it had long been known that magnetic fields could affect the electrical resistance of magnetic materials like iron. Current flowed more easily along the field lines than across them.
While this effect on electrical resistance was useful for sensing magnetic fields and, in electronic heads, reading magnetic disks, it amounted to only a small change in the resistance, and physicists did not think there were many prospects for improvement.
So it was a surprise in 1988 when groups led by Dr. Fert at the Laboratoire de Physique des Solides in Paris and by Dr. Grünberg found that super-slim sandwiches of iron and chromium that they had assembled showed large sensitivity to magnetic fields — or “giant magnetoresistance,” as Dr. Fert called it. The name stuck.
The reason for the effect has to do with what physicists call the spin of electrons — their somewhat mysterious ability to have an orientation in space. When the magnetic layers of the sandwich have both their fields pointing in the same direction, electrons whose spin points along that direction can migrate freely through the sandwich. Electrons that point in another direction, however, are scattered.
If, however, one of the magnetic layers is perturbed by, say, reading a small signal, it can flip its direction so that its field runs opposite to the other one; this dramatically increases the electrical resistance of the sandwich.
As Philip Schewe, of the American Institute of Physics, explained, “You’ve leveraged a weak bit of magnetism into a robust bit of electricity.”
Experts said the discovery was one of the first triumphs of the new field of nanotechnology, the ability to build and manipulate assemblies of atoms only a nanometer (a billionth of a meter) in size.

For the full obituary, see:
DENNIS OVERBYE. “Peter Grünberg, 78, Dies; Heart of Modern Gadgets Is Based on His Research.” The New York Times (Friday, April 13, 2018): A25.
(Note: ellipsis added.)
(Note: the online version of the obituary has the date APRIL 12, 2018, and has the title “Peter Grünberg, 78, Winner of an ‘iPod Nobel,’ Is Dead.”)

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