Effects of Hydrostatic Pressure on the Properties of Magnetic Materials

A review of the literature on hydrostatic pressure effects on magnetic materials showed a lack of information on technologically important properties such as initial permeability, and the hysteresis loop. Measurements of these properties up to 20000 psi showed that most solid materials are only slightly affected. These include tape cores of supermalloy, supermendur, 4–79 Mo-permalloy and grain-oriented Si-steel, as well as S-5 ferrite memory cores, and compressed powder cores of 2–81 Mo-permalloy or of carbonyl iron. Some types of NiZn and MnZn ferrite show increase of coercive force and decrease of permeability with pressure. Measurements were made of permeability vs frequency of MnZn ferrite to find the relaxation frequency. At atmospheric pressure, the permeability shows a sharp decline above 0.85 Mc. At 20000 psi the decline in permeability does not occur until 1.6 Mc.