Magnetic Noise Spectrum Research Articles

Preliminary results from the Ogo 1 Search Coil Magnetometer: Boundary positions and magnetic noise spectra

The Ogo 1 triaxial search coil magnetometer was designed to study natural magnetic fluctuations from 0.01 to 1000 cps in the vicinity of the earth. This frequency range was chosen in order to explore the magnetic spectrum between the ranges previously explored in space by dc magnetometers and extremely low frequency electromagnetic equipment. The highly eccentric Ogo 1 orbit makes possible an investigation of time-varying magnetic fields in the magnetosphere, the magnetosheath (transition region), and the interplanetary medium. The preliminary analysis of the data reported here concerns: (1) the character and location of the magnetopause and hydromagnetic bow shock over portions of the subsolar hemisphere, and (2) the characteristics of broad band magnetic noise detected in the magnetosheath behind the bow shock.

Magnetic Fluctuations in Molybdenum Permalloy

Considerations of generalized noise and magnetic viscosity suggest the existence of magnetic fluctuations in ferromagnets. Magnetic fluctuations in molybdenum Permalloy tape ring cores have been detected by observing noise voltages at the terminals of a coil wound on the sample. For thin tape cores and at low frequencies, the observed magnetic noise spectrum is in excess of Nyquist noise and is characteristic of a slow relaxation phenomenon with an activation energy of 0.04 ev. For thick tape cores and at high frequencies, core losses yield noise voltages in agreement with Nyquist's law and provide a means of studying ferromagnetic loss with zero magnetic excitation.