Hall Effect of Fame

Edwin Hall The Hall Effect is beloved of condensed matter physicists the world over for its use in characterisation of materials and sensing of magnetic fields. Now found in pretty much any condensed matter textbook, its relations such as the spin hall effect and the anomalous hall effect form the basis of many spintronic devices, studies and investigations.

Spintronics owes much to the discovery of the Hall effect, and Edwin Hall’s original paper from 1879 is a delightful insight into the sense of excitement and wonder that must have been present in the field of physics at the time.

A Familiar Relationship

Hall’s interest in electromagnetism was piqued by some of the statements of that other great physicist of the time, James Clerk Maxwell. Hall felt moved to set about a series of experiments to investigate the effect of magnetic field on electric current.

In his paper Hall leads us through his thought processes as he develops his experiments and how, despite one or two false starts, he eventually arrives at the conclusion that would have such an impact in condensed matter physics.

Hall’s concluding experiment is one that many condensed matter physicists would recognise today: a thin film of gold, a current source and a voltmeter.

Hall Effect Diagram

Hall arrived at an experiment that is familar to us even today. He uses apparatus invented by William Thomsom, who discovered AMR, and Bunsen, inventor of the Bunsen burner.

Even with this relatively crude apparatus, Hall is able to reach the now familiar conclusion:

the action on the Thomson galvanometer is proportional to the product of the magnetic force by the current through the cold leaf

We now know the constant of proportionality to be the inverse of the product of the electronic charge, the number of charge carriers and the thickness of the film studied. It is this last term that meant that Hall struggled to measure his effect on his earlier samples.

A Trio of Supporting Scientists

It turns out this work of Hall into the effect of magnetic fields on electrical currents was supported by a trio of other key scientists of the age. We have already seen that the work was inspired by Maxwell, and rather interestingly the Thomson Galvanometer Hall refers to is none other than William “Later Lord Kelvin” Thomson, discoverer of anisotropic magnetoresistance (AMR). To complete this trio of 19th century greats, Hall and Thomson are joinealso uses “Bunsen’s Cell“, a battery invented by the same man who invented the Bunsen burner – used in chemistry labs all over the world!

Hall E.H. (1879). On a New Action of the Magnet on Electric Currents, American Journal of Mathematics, 2 (3) 287. DOI: http://dx.doi.org/10.2307/2369245

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