In 1879 Edwin H. Hall discovered that when he placed a conducting strip carrying a current in a magnetic field, a potential difference was produced across the strip - transverse to the current and magnetic field directions. At the time, Hall was a 24-year-old graduate student working under Henry A. Rowland at Johns Hopkins University. The discovery of the electron was still over a decade away and the results of Hall’s experiments were poorly understood at best. Nonetheless, the effect that now bears Hall’s name was at a watershed in the history of physics. It was one the first experiments to show that charge carriers of an electric current were negative and hinted at greater things to come.
Magnetoresistance is the changing of a substance’s resistance in the presence of a magnetic field. The early history of magnetoresistance is not documented very well, but it is probably safe to assume that the effect was noticed in the same time frame as the Hall Effect. "Normal" magnetoresistance, the more common version, involves a change in resistance on the order of 1%. Recently, new types of magnetoresistance have been discovered. In the late 1980s two European scientists working independently, Peter Gruenberg of the KFA research institute in Julich, Germany, and Albert Fert of the University of Paris, discovered what was to be called giant magnetoresistance (GMR). They saw resistance changes of 6 to 50% in composite materials. Recently scientists have discovered magnetoresistive effects on the order of 1000% - so-called colossal magnetoresistance (CMR).
This lab investigates both the Hall and magnetoresistance effects at varying temperatures. Data will be taken using the computer interface and output in spreadsheet form. While the computer facilitates taking accurate data rapidly and allows an emphasis on the fundamental physics and analysis, its use should not replace an understanding of the experimental setup and procedure.
| School of Physics at Georgia Tech |