Initial Phase

Pierre began his voyage of scientific researches at the age of 19. He carried out his first work on the calculation of the wavelength of heat waves. At the beginning of his career, he worked as a laboratory assistant to Professor P. Desains in the faculty of science. In 1880, he conducted his first research in the determination of the wavelengths of infrared rays, using a novel system of a thermocouple and a metallic wire grating. This process was entirely new at that time, and it has since often been used in the study of this subject.

Following the work on wavelength rays, he undertook an investigation on crystals in collaboration with his brother Jacques, who was a preparator for Friedel’s laboratory of mineralogy at the Sorbonne. Their fruitful collaboration led the two young physicists towards a great success, the discovery of piezo-electricity. This unknown phenomenon consisted of an electric polarization produced by the compression or the expansion of crystals in the direction of axis of symmetry. The Curie brothers succeeded in carrying out a complete study of the new phenomenon :

"Some crystals, when compressed in particular directions show positive and negative charges on their surfaces, the charges being proportional to the pressure and disappearing when the pressure is withdrawn."

While experimenting piezo-electricity, Pierre and Jacques were obliged to employ electrometric apparatus. In those days, the quadrant electrometer was very well known, but they could not use it. So they developed a new version, better adapted to their requirements. This instrument become popular in France as the Curie electrometer – the forerunner of modern quartz controls for timepieces and radio transmitters.

Second Phase

In 1882, working as a supervisor at the school of physics in Paris, Pierre carried out his own research. For a long period, he studied buffered movements. These first years of independent research were arduous. It was the second phase of his career, when he conducted fruitful research on crystals and magnetism. He advanced theories of symmetry with regard to certain physical phenomena and turned his attention to magnetism.

In 1885, he published his research papers on the theoretical relations between crystallography and physics. Pierre, with his brother, established the conditions of symmetry required for its production in crystals and stated its notably simple quantitative laws as well as its absolute magnitude for particular crystals. Pierre formulated the principle of symmetry, which states the impossibility of bringing about a specific physical process in an environment lacking a certain minimal dis-symmetry characteristic of the process. This principle became one of the ultra-sensitive scientific scale, the Curie scale. Many eminent foreign scientists including Roentgen, Kundt, Voigt and Riecke followed the new road opened by the Curie brothers and made further investigations.

In 1894, he obtained his doctorate with a thesis on the magnetic properties of materials. He undertook research on magnetism and obtained a result of capital importance. He managed to perfect the analytical balance by creating a periodic balance with direct reading of the last weights. Then he concentrated on magnetism. He explained if there was any existence of some relation between the three types of magnetism : Ferromagnetism, paramagnetism and diamagnetism. It led to the discovery of a fundamental law, known as the Curie’s Law.

This law states : "The properties of diamagnetic materials are generally independent of temperature but for paramagnetic material the susceptibility is inversely proportional to the absolute temperature."

The temperature at which the transition from ferromagnetism to paramagnetism takes place is known today as Curie point. Pierre demonstrated the totally different character of diamagnetism and paramagnetism, which was later explained theoretically by Paul Langevin.