The Kinetics of the Curie Transition in Nickel.

The specific heat of nickel has been measured near the Curie temperature ((DBLTURN) 631(DEGREES) K). The temperature was achieved by the use of an alternating heating current and the temperature fluctuations of the sample were measured by an infrared radiation detector. Measurements were made at heating current frequencies of 10 Hertz and 105 Hertz. Those at 10 Hertz agree quite well with measurements done with entirely different methods, but those at 105 Hertz show lower specific heat and less of an anomaly near the critical point than those at the low frequency. This data suggests the existence of critical superparamagnetism with relaxation times on the order of milliseconds in the nickel. The method of specific heat determination presented provides the possible capability of using heating frequencies on the order of 10,000 Hertz so that the kinetics of transitions can be studied.