# Paul Langevin

| Paul Langevin (1872 – 1946) was one of the fathers of magnetism.
|  | In the "miracle year" 1905, when Einstein published three revolutionary papers, Langevin published his theory of para- and diamagnetism.
|  | Considering that quantum theory had yet to be discovered, and that statitical thermodynamics was in its infancy, his contribution was of amazing insight.
|  | As far as paramgnetism was concerned, he first established the treatment we used in the text for orientaiio polarization (which is formally indenticl to paramagnetism).
| The resulting function of the form L(a) = –1/a + coth(a) is therfore called teh Langevin functions (or sometime Langevin-Debye function, since Debye used the same procedure somerwhat later for polar molecules).
| Langevin also worked in the field of Brownian motion (like Einstein). His work concerning ultrasonic sound during world war I was the base for sonar technology .

With frame

3.2.4 Orientation Polarization

© H. Föll (Electronic Materials - Script)